Neonatal seizure: Limited data available: Note: Use has been replaced by other agents; in neonates, hepatic conversion to phenobarbital is virtually absent and generally not recommended for treatment of neonatal seizures (Battino 1995); primidone serum levels should be used for therapeutic drug monitoring (Sapin 1988). Oral: 12 to 20 mg/kg/day in 2 to 4 divided doses; start with lower dosage and titrate upward (Nelson 1996; Powell 1984).
Seizure disorder (generalized tonic-clonic, psychomotor, and focal):
Weight-directed: Infants and Children <8 years: Oral: Usual maintenance range: 10 to 25 mg/kg/day in 2 to 3 divided doses; start with lower dosage and titrate upward; usual maximum dose: 500 mg/dose (Kliegman 2016)
Fixed dosing:
Children <8 years: Oral:
Initial: Days 1 to 3: 50 mg at bedtime; Days 4 to 6: 50 mg twice daily; Days 7 to 9: 100 mg twice daily
Maintenance (starting Day 10 of therapy): 125 to 250 mg three times daily
Patients already receiving other antiseizure medications: Specific recommendations in this age group are not available. However, in older pediatric patients (≥8 years of age), the usual initial starting dose is recommended, and then gradually increase primidone to maintenance dose as other drug is gradually decreased, continue until desired level obtained or other drug completely withdrawn. If goal is monotherapy, conversion should be completed over ≥2 weeks.
Children ≥8 years and Adolescents: Oral:
Initial: Days 1 to 3: 100 to 125 mg at bedtime; Days 4 to 6: 100 to 125 twice daily; Days 7 to 9: 100 to 125 mg 3 times daily
Maintenance (starting Day 10 of therapy): 250 mg 3 times daily; adjust dose to usual maintenance range: 750 to 1,000 mg/day in divided doses 3 to 4 times daily; some patients may require 1,500 mg/day in divided doses 4 times daily; maximum daily dose: 2,000 mg/day
Patients already receiving other antiseizure medications: Initial: 100 to 125 mg at bedtime; gradually increase to maintenance dose as other drug is gradually decreased, continue until desired level obtained or other drug completely withdrawn. If goal is monotherapy, conversion should be completed over ≥2 weeks.
There are no dosage adjustments provided in manufacturer’s labeling. Avoid in renal failure if possible; due to active metabolites with long half-lives and complex kinetics; based on experience in adult patients, dosing adjustment suggested
There are no dosage adjustments provided in manufacturer’s labeling. However, increased side effects may occur in severe liver disease; monitor plasma levels and adjust dose accordingly.
(For additional information see "Primidone: Drug information")
Seizure disorders (grand mal, psychomotor, and focal): Oral: Days 1 to 3: 100 to 125 mg/day at bedtime; days 4 to 6: 100 to 125 twice daily; days 7 to 9: 100 to 125 mg 3 times daily; usual dose: 750 to 1,500 mg/day in divided doses 3 to 4 times/day with maximum dosage of 2 g/day
Patients already receiving other antiseizure medications: Initial: 100 to 125 mg at bedtime; gradually increase to maintenance dose as other drug is gradually decreased, continue until desired level obtained or other drug completely withdrawn. If goal is monotherapy, conversion should be completed over ≥2 weeks.
Essential tremor (off-label use): Oral: Initial: 25 mg once daily; increase dose gradually (eg, every 3 to 7 days) based on response and tolerability in increments of 25 mg. Usual dosage: 150 to 250 mg/day in 1 or 2 divided doses. Doses of up to 750 mg/day have been studied, but some experts recommend a maximum of 250 to 500 mg/day due to dose-related adverse drug reactions (Abboud 2011; Deik 2022; Deuschl 2011; Findley 1985; Serrano-Duenas 2003; Shanker 2019).
No dosage adjustment provided in manufacturer's labeling. However, the following recommendations (based on a maximum of 750 mg twice daily in normal kidney function) have been used by some clinicians: Note: Avoid in renal failure if possible; due to active metabolites with long half-lives and complex kinetics (Aronoff 2007):
GFR ≥50 mL/minute: No dosage adjustment necessary.
GFR 10 to 50 mL/minute: Administer no more frequently than every 12 to 24 hours (Aronoff 2007).
GFR <10 mL/minute: Administer no more frequently than every 24 hours (Aronoff 2007).
Hemodialysis: Dialyzable (Lee 1982). Administer dose after dialysis due to high extraction during hemodialysis or may administer a supplemental dose prior to dialysis session that is 30% of the patient's usual dose (Aronoff 2007; Asconapé 2014; Lee 1982).
No dosage adjustment provided in manufacturer’s labeling. However, increased side effects may occur in severe liver disease; monitor plasma levels and adjust dose accordingly.
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Tablet, Oral:
Mysoline: 50 mg, 250 mg [scored]
Generic: 50 mg, 250 mg
Yes
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Tablet, Oral:
Generic: 125 mg, 250 mg
An FDA-approved patient medication guide, which is available with the product information and at http://www.fda.gov/downloads/Drugs/DrugSafety/UCM222370.pdf, must be dispensed with this medication.
Oral: Administer without regard to food; may consider food to decrease GI upset
Store at 20°C to 25°C (68°F to 77°F).
Treatment of generalized tonic-clonic (grand mal), psychomotor, and focal seizures as monotherapy or in combination with other antiseizure agents (FDA approved in children and adults)
Primidone may be confused with predniSONE, primaquine, pyridoxine
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.
Frequency not defined.
Central nervous system: Ataxia, drowsiness, emotional disturbance, fatigue, hyperirritability, suicidal ideation, vertigo
Dermatologic: Morbilliform rash
Gastrointestinal: Anorexia, nausea, vomiting
Genitourinary: Impotence
Hematologic & oncologic: Agranulocytosis, granulocytopenia, megaloblastic anemia (idiosyncratic), pure red cell aplasia, red cell hypoplasia
Ophthalmic: Diplopia, nystagmus
Hypersensitivity to phenobarbital; porphyria
Concerns related to adverse effects:
• CNS depression: May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks that require mental alertness (eg, operating machinery, driving).
• Suicidal ideation: Pooled analysis of trials involving various antiseizure medications (regardless of indication) showed an increased risk of suicidal thoughts/behavior (incidence rate: 0.43% treated patients compared to 0.24% of patients receiving placebo); risk observed as early as 1 week after initiation and continued through duration of trials (most trials ≤24 weeks). Monitor all patients for notable changes in behavior that might indicate suicidal thoughts or depression; notify health care provider immediately if symptoms occur.
Disease-related concerns:
• Depression: Use with caution in patients with depression or suicidal tendencies.
• Hepatic impairment: Use with caution in patients with hepatic impairment.
• Hypoadrenalism: Use with caution in patients with hypoadrenalism.
• Renal impairment: Use with caution in patients with renal impairment.
• Respiratory disease: Use with caution in patients with respiratory disease.
• Substance abuse: Use with caution in patients with a history of drug abuse; potential for drug dependency exists. Tolerance or psychological and physical dependence may occur with prolonged use.
Concurrent drug therapy issues:
• Sedatives: Effects with other sedative drugs or ethanol may be potentiated.
Special populations:
• Debilitated patients: Use with caution in patients who are debilitated; may cause paradoxical responses.
• Elderly: Use with caution in elderly patients due to sedating side effects and cognitive function declines. Primidone may cause paradoxical responses.
• Pediatric: Primidone's active metabolite, phenobarbital, has been associated with cognitive deficits in children receiving chronic therapy for febrile seizures.
Dosage form specific issues:
• Benzyl alcohol and derivatives: Some dosage forms may contain sodium benzoate/benzoic acid; benzoic acid (benzoate) is a metabolite of benzyl alcohol; large amounts of benzyl alcohol (≥99 mg/kg/day) have been associated with a potentially fatal toxicity ("gasping syndrome") in neonates; the "gasping syndrome" consists of metabolic acidosis, respiratory distress, gasping respirations, CNS dysfunction (including convulsions, intracranial hemorrhage), hypotension, and cardiovascular collapse (AAP ["Inactive" 1997]; CDC 1982); some data suggest that benzoate displaces bilirubin from protein binding sites (Ahlfors 2001); avoid or use dosage forms containing benzyl alcohol derivative with caution in neonates. See manufacturer's labeling.
Other warnings/precautions:
• Acute pain: Do not administer to patients in acute pain.
• Withdrawal: Antiseizure medications should not be discontinued abruptly because of the possibility of increasing seizure frequency; therapy should be withdrawn gradually to minimize the potential of increased seizure frequency, unless safety concerns require a more rapid withdrawal.
One of the active metabolites of primidone is phenobarbital. Phenobarbital may cause CNS depression and effects with other sedative drugs may be potentiated. Phenobarbital has been associated with cognitive deficits in children receiving therapy for complicated febrile seizures. Cognitive deficits observed with phenobarbital were further described in a retrospective chart review of 280 pediatric patients who had received either phenobarbital, levetiracetam, or both for treatment of neonatal seizures. A subset of the study group (n=67) had a Bayley Scales of Infant Development (BSID) completed at 24 months corrected age. Based on the analysis of cumulative exposures, the investigators observed that increased phenobarbital exposure was associated with a significant decrease in BSID cognitive (8 points) and motor (9 points) scores and an increased probability for the development of cerebral palsy (2.3-fold) for every 100 mg/kg of phenobarbital exposure (Maitre 2013).
Pediatric patients may be at increased risk for vitamin D deficiency; with chronic therapy, phenobarbital may cause catabolism of vitamin D; the daily vitamin D requirement may be increased in these patients (≥400 units/day); vitamin D status should be periodically monitored with laboratory data (Misra 2008; Wagner 2008).
Substrate of CYP2C19 (minor); Note: Assignment of Major/Minor substrate status based on clinically relevant drug interaction potential; Induces CYP1A2 (weak), CYP2A6 (weak), CYP2B6 (weak), CYP2C9 (weak), CYP3A4 (strong), UGT1A1
Abemaciclib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Abemaciclib. Risk X: Avoid combination
Abiraterone Acetate: CYP3A4 Inducers (Strong) may decrease the serum concentration of Abiraterone Acetate. Management: Avoid whenever possible. If such a combination cannot be avoided, increase abiraterone acetate dosing frequency from once daily to twice daily during concomitant use. Risk D: Consider therapy modification
Acalabrutinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Acalabrutinib. Management: Avoid co-administration of strong CYP3A inducers in patients taking acalabrutinib. If strong CYP3A inducers cannot be avoided, increase the dose of acalabrutinib to 200 mg twice daily. Risk D: Consider therapy modification
Acetaminophen: Primidone may increase the metabolism of Acetaminophen. Specifically, formation of the hepatotoxic NAPQI metabolite may be increased. Risk C: Monitor therapy
Afatinib: Primidone may decrease the serum concentration of Afatinib. Management: Consider increasing the afatinib dose by 10 mg as tolerated in patients requiring chronic coadministration of phenobarbital with afatinib. Reduce afatinib dose back to the original afatinib dose 2 to 3 days after discontinuation of phenobarbital. Risk D: Consider therapy modification
Alcohol (Ethyl): CNS Depressants may enhance the CNS depressant effect of Alcohol (Ethyl). Risk C: Monitor therapy
Alfacalcidol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Alfacalcidol. Risk C: Monitor therapy
Alfentanil: CYP3A4 Inducers (Strong) may decrease the serum concentration of Alfentanil. Management: If concomitant use of alfentanil and strong CYP3A4 inducers is necessary, consider dosage increase of alfentanil until stable drug effects are achieved. Monitor patients for signs of opioid withdrawal. Risk D: Consider therapy modification
Alizapride: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Alpelisib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Alpelisib. Risk X: Avoid combination
ALPRAZolam: CYP3A4 Inducers (Strong) may decrease the serum concentration of ALPRAZolam. Risk C: Monitor therapy
Amiodarone: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Amiodarone. CYP3A4 Inducers (Strong) may decrease the serum concentration of Amiodarone. Risk C: Monitor therapy
AmLODIPine: CYP3A4 Inducers (Strong) may decrease the serum concentration of AmLODIPine. Risk C: Monitor therapy
Antihepaciviral Combination Products: CYP3A4 Inducers (Strong) may decrease the serum concentration of Antihepaciviral Combination Products. Risk X: Avoid combination
Apixaban: CYP3A4 Inducers (Strong) may decrease the serum concentration of Apixaban. Management: Avoid concurrent use of apixaban with strong CYP3A4 inducers whenever possible. Use of a strong CYP3A4 inducer with apixaban should be strictly avoided in any patient who is using an agent (either the CYP3A4 inducer or a third drug) that induces P-gp. Risk D: Consider therapy modification
Apremilast: CYP3A4 Inducers (Strong) may decrease the serum concentration of Apremilast. Risk X: Avoid combination
Aprepitant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Aprepitant. Risk X: Avoid combination
ARIPiprazole: CYP3A4 Inducers (Strong) may decrease the serum concentration of ARIPiprazole. Management: For indications other than major depressive disorder: double the oral aripiprazole dose over 1 to 2 weeks and closely monitor. Avoid use of strong CYP3A4 inducers for more than 14 days with extended-release injectable aripiprazole. Risk D: Consider therapy modification
ARIPiprazole Lauroxil: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of ARIPiprazole Lauroxil. Management: Patients taking the 441 mg dose of aripiprazole lauroxil increase their dose to 662 mg if used with a strong CYP3A4 inducer for more than 14 days. No dose adjustment is necessary for patients using the higher doses of aripiprazole lauroxil. Risk D: Consider therapy modification
Artemether and Lumefantrine: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Artemether and Lumefantrine. Specifically, concentrations of dihydroartemisinin (DHA), the active metabolite of artemether may be decreased. CYP3A4 Inducers (Strong) may decrease the serum concentration of Artemether and Lumefantrine. Risk X: Avoid combination
Asunaprevir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Asunaprevir. Risk X: Avoid combination
Atazanavir: Primidone may decrease the serum concentration of Atazanavir. Atazanavir may decrease the serum concentration of Primidone. Management: Coadministration of primidone and atazanavir without ritonavir is not recommended. If atazanavir and ritonavir are coadministered with primidone, primidone dose increases may be required. Risk D: Consider therapy modification
Atogepant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Atogepant. Management: The recommended dose of atogepant is 30 mg once daily or 60 mg once daily when combined with strong or moderate CYP3A4 inducers. Risk D: Consider therapy modification
Atorvastatin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Atorvastatin. Risk C: Monitor therapy
Avacopan: CYP3A4 Inducers (Strong) may decrease the serum concentration of Avacopan. Risk X: Avoid combination
Avanafil: CYP3A4 Inducers (Strong) may decrease the serum concentration of Avanafil. Risk X: Avoid combination
Avapritinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Avapritinib. Risk X: Avoid combination
Axitinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Axitinib. Risk X: Avoid combination
Azelastine (Nasal): May enhance the CNS depressant effect of CNS Depressants. Risk X: Avoid combination
Barbiturates: Primidone may enhance the adverse/toxic effect of Barbiturates. Primidone is converted to phenobarbital, and thus becomes additive with existing barbiturate therapy. Risk C: Monitor therapy
Barnidipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Barnidipine. Risk C: Monitor therapy
Bazedoxifene: Primidone may decrease the serum concentration of Bazedoxifene. This may lead to loss of efficacy or, if bazedoxifene is combined with estrogen therapy, an increased risk of endometrial hyperplasia. Risk C: Monitor therapy
Bedaquiline: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Bedaquiline. CYP3A4 Inducers (Strong) may decrease the serum concentration of Bedaquiline. Risk X: Avoid combination
Belumosudil: CYP3A4 Inducers (Strong) may decrease the serum concentration of Belumosudil. Management: Increase the dose of belumosudil to 200 mg twice daily when coadministered with strong CYP3A4 inducers. Risk D: Consider therapy modification
Benidipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Benidipine. Risk C: Monitor therapy
Benperidol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Benperidol. Risk C: Monitor therapy
Benzhydrocodone: Primidone may enhance the CNS depressant effect of Benzhydrocodone. Primidone may decrease serum concentrations of the active metabolite(s) of Benzhydrocodone. Specifically, serum concentrations of hydrocodone may be decreased. Management: Avoid use of benzhydrocodone and primidonel when possible. Monitor for respiratory depression/sedation. Because primidone is also a strong CYP3A4 inducer, monitor for decreased benzhydrocodone efficacy and withdrawal if combined. Risk D: Consider therapy modification
Betamethasone (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Betamethasone (Systemic). Risk C: Monitor therapy
Bictegravir: Primidone may decrease the serum concentration of Bictegravir. Management: When possible consider using an alternative antiseizure drug with concurrent bictegravir, emtricitabine, and tenofovir alafenamide. If the combination must be used, monitor closely for evidence of reduced antiviral effectiveness. Risk D: Consider therapy modification
Bisoprolol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Bisoprolol. Risk C: Monitor therapy
Blonanserin: CNS Depressants may enhance the CNS depressant effect of Blonanserin. Management: Use caution if coadministering blonanserin and CNS depressants; dose reduction of the other CNS depressant may be required. Strong CNS depressants should not be coadministered with blonanserin. Risk D: Consider therapy modification
Blood Pressure Lowering Agents: Barbiturates may enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy
Bortezomib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Bortezomib. Risk X: Avoid combination
Bosutinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Bosutinib. Risk X: Avoid combination
Brentuximab Vedotin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Brentuximab Vedotin. Specifically, concentrations of the active monomethyl auristatin E (MMAE) component may be decreased. Risk C: Monitor therapy
Brexanolone: CNS Depressants may enhance the CNS depressant effect of Brexanolone. Risk C: Monitor therapy
Brexpiprazole: CYP3A4 Inducers (Strong) may decrease the serum concentration of Brexpiprazole. Management: If brexpiprazole is used together with a strong CYP3A4 inducer, the brexpiprazole dose should gradually be doubled over the course of 1 to 2 weeks. Decrease brexpiprazole to original dose over 1 to 2 weeks if the strong CYP3A4 inducer is discontinued. Risk D: Consider therapy modification
Brigatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Brigatinib. Risk X: Avoid combination
Brimonidine (Topical): May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Brivaracetam: Primidone may decrease the serum concentration of Brivaracetam. Risk C: Monitor therapy
Bromocriptine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Bromocriptine. Risk C: Monitor therapy
Bromopride: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Bromperidol: May enhance the CNS depressant effect of CNS Depressants. Risk X: Avoid combination
Buprenorphine: Primidone may enhance the CNS depressant effect of Buprenorphine. Primidone may decrease the serum concentration of Buprenorphine. Management: Avoid use of buprenorphine and primidone when possible. Monitor for respiratory depression/sedation. Because primidone is also a strong CYP3A4 inducer, monitor for decreased buprenorphine efficacy and withdrawal if combined. Risk D: Consider therapy modification
BuPROPion: CYP2B6 Inducers (Weak) may decrease the serum concentration of BuPROPion. Risk C: Monitor therapy
BusPIRone: CYP3A4 Inducers (Strong) may decrease the serum concentration of BusPIRone. Management: Consider alternatives to this combination. If coadministration of these agents is deemed necessary, monitor patients for reduced buspirone effects and increase buspirone doses as needed. Risk D: Consider therapy modification
Cabazitaxel: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cabazitaxel. Risk C: Monitor therapy
Cabotegravir: UGT1A1 Inducers may decrease the serum concentration of Cabotegravir. Risk X: Avoid combination
Cabozantinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cabozantinib. Management: Avoid use of strong CYP3A4 inducers with cabozantinib if possible. If combined, increase cabozantinib capsules (Cometriq) by 40 mg from previous dose, max 180 mg daily. Increase cabozantinib tablets (Cabometyx) by 20 mg from previous dose, max 80 mg daily Risk D: Consider therapy modification
Calcifediol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Calcifediol. Risk C: Monitor therapy
Calcitriol (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Calcitriol (Systemic). Risk C: Monitor therapy
Canagliflozin: Primidone may decrease the serum concentration of Canagliflozin. Management: Consider increasing canagliflozin dose to 200 mg/day in patients tolerating 100 mg/day. A further increase to 300 mg/day can be considered in patients with an estimated glomerular filtration rate (GFR) of 60 mL/min/1.73 m2 or greater. Risk D: Consider therapy modification
Cannabidiol: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Cannabidiol. CYP3A4 Inducers (Strong) may decrease the serum concentration of Cannabidiol. Risk C: Monitor therapy
Cannabinoid-Containing Products: CNS Depressants may enhance the CNS depressant effect of Cannabinoid-Containing Products. Risk C: Monitor therapy
Cannabis: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cannabis. More specifically, tetrahydrocannabinol and cannabidiol serum concentrations may be decreased. Risk C: Monitor therapy
Capmatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Capmatinib. Risk X: Avoid combination
CarBAMazepine: CYP3A4 Inducers (Strong) may decrease the serum concentration of CarBAMazepine. Risk C: Monitor therapy
Carbonic Anhydrase Inhibitors: May enhance the adverse/toxic effect of Primidone. Specifically, osteomalacia and rickets. Carbonic Anhydrase Inhibitors may decrease the serum concentration of Primidone. Risk C: Monitor therapy
Cariprazine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cariprazine. Risk X: Avoid combination
Ceritinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ceritinib. Risk X: Avoid combination
Chloramphenicol (Systemic): May increase serum concentrations of the active metabolite(s) of Primidone. Specifically, the concentrations of phenobarbital may be increased. Primidone may decrease the serum concentration of Chloramphenicol (Systemic). Risk C: Monitor therapy
Chlormethiazole: May enhance the CNS depressant effect of CNS Depressants. Management: Monitor closely for evidence of excessive CNS depression. The chlormethiazole labeling states that an appropriately reduced dose should be used if such a combination must be used. Risk D: Consider therapy modification
Chlorphenesin Carbamate: May enhance the adverse/toxic effect of CNS Depressants. Risk C: Monitor therapy
ChlorproPAMIDE: CYP3A4 Inducers (Strong) may decrease the serum concentration of ChlorproPAMIDE. Risk C: Monitor therapy
Cilnidipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cilnidipine. Risk C: Monitor therapy
Citalopram: CYP3A4 Inducers (Strong) may decrease the serum concentration of Citalopram. Risk C: Monitor therapy
Clarithromycin: CYP3A4 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Clarithromycin. CYP3A4 Inducers (Strong) may decrease the serum concentration of Clarithromycin. Management: Consider alternative antimicrobial therapy for patients receiving a CYP3A4 inducer. Drugs that enhance the metabolism of clarithromycin into 14-hydroxyclarithromycin may alter the clinical activity of clarithromycin and may impair clarithromycin efficacy. Risk D: Consider therapy modification
Clindamycin (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Clindamycin (Systemic). Risk C: Monitor therapy
ClonazePAM: CYP3A4 Inducers (Strong) may decrease the serum concentration of ClonazePAM. Risk C: Monitor therapy
CloZAPine: CYP3A4 Inducers (Strong) may decrease the serum concentration of CloZAPine. Management: Avoid use with strong CYP3A4 inducers when possible. If combined, monitor patients closely and consider clozapine dose increases. Clozapine dose reduction and further monitoring may be required when strong CYP3A4 inducers are discontinued. Risk D: Consider therapy modification
CNS Depressants: May enhance the adverse/toxic effect of other CNS Depressants. Risk C: Monitor therapy
Cobicistat: Primidone may decrease the serum concentration of Cobicistat. Risk X: Avoid combination
Cobimetinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cobimetinib. Risk X: Avoid combination
Codeine: Primidone may enhance the CNS depressant effect of Codeine. Primidone may decrease the serum concentration of Codeine. Management: Avoid use of codeine and primidone when possible. Monitor for respiratory depression/sedation. Because primidone is also a strong CYP3A4 inducer, monitor for decreased codeine efficacy and withdrawal if combined. Risk D: Consider therapy modification
Copanlisib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Copanlisib. Risk X: Avoid combination
Cosyntropin: May enhance the hepatotoxic effect of Primidone. Risk C: Monitor therapy
Crizotinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Crizotinib. Risk X: Avoid combination
CycloSPORINE (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of CycloSPORINE (Systemic). Management: Monitor closely for reduced cyclosporine concentrations when combined with strong CYP3A4 inducers. Cyclosporine dose increases will likely be required to maintain adequate serum concentrations. Risk D: Consider therapy modification
Cyproterone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cyproterone. Risk C: Monitor therapy
Dabigatran Etexilate: Primidone may decrease the serum concentration of Dabigatran Etexilate. Risk C: Monitor therapy
Daclatasvir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Daclatasvir. Risk X: Avoid combination
Dapsone (Systemic): May enhance the adverse/toxic effect of CYP3A4 Inducers (Strong). CYP3A4 Inducers (Strong) may decrease the serum concentration of Dapsone (Systemic). Risk C: Monitor therapy
Daridorexant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Daridorexant. Risk X: Avoid combination
Darunavir: May decrease the serum concentration of Primidone. Risk C: Monitor therapy
Dasabuvir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dasabuvir. Risk X: Avoid combination
Dasatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dasatinib. Management: Avoid concurrent use of dasatinib with strong CYP3A4 inducers when possible. If such a combination cannot be avoided, consider increasing dasatinib dose and monitor clinical response and toxicity closely. Risk D: Consider therapy modification
Deflazacort: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Deflazacort. Risk X: Avoid combination
Delamanid: CYP3A4 Inducers (Strong) may decrease the serum concentration of Delamanid. Risk X: Avoid combination
Delavirdine: Primidone may decrease the serum concentration of Delavirdine. Risk X: Avoid combination
Desmopressin: Hyponatremia-Associated Agents may enhance the hyponatremic effect of Desmopressin. Risk C: Monitor therapy
DexAMETHasone (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of DexAMETHasone (Systemic). Management: Consider dexamethasone dose increases in patients receiving strong CYP3A4 inducers and monitor closely for reduced dexamethasone efficacy. Consider avoiding this combination when treating life threatening conditions (ie, multiple myeloma). Risk D: Consider therapy modification
Dexmethylphenidate: May increase serum concentrations of the active metabolite(s) of Primidone. Specifically, phenobarbital concentrations could become elevated. Dexmethylphenidate may increase the serum concentration of Primidone. Risk C: Monitor therapy
DiazePAM: CYP3A4 Inducers (Strong) may decrease the serum concentration of DiazePAM. Risk C: Monitor therapy
Difelikefalin: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
DilTIAZem: CYP3A4 Inducers (Strong) may decrease the serum concentration of DilTIAZem. Management: Consider alternatives to this combination when possible. If combined, monitor for decreased diltiazem efficacy. Risk D: Consider therapy modification
Dimethindene (Topical): May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Disopyramide: CYP3A4 Inducers (Strong) may decrease the serum concentration of Disopyramide. Risk C: Monitor therapy
Dolutegravir: Primidone may decrease the serum concentration of Dolutegravir. Specifically, the Primidone metabolite phenobarbital may decrease Dolutegravir serum concentrations. Risk X: Avoid combination
Domperidone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Domperidone. Risk C: Monitor therapy
Doravirine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Doravirine. Risk X: Avoid combination
Doxercalciferol: CYP3A4 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Doxercalciferol. Risk C: Monitor therapy
DOXOrubicin (Conventional): CYP3A4 Inducers (Strong) may decrease the serum concentration of DOXOrubicin (Conventional). Risk X: Avoid combination
Doxycycline: Barbiturates may decrease the serum concentration of Doxycycline. Risk C: Monitor therapy
Doxylamine: May enhance the CNS depressant effect of CNS Depressants. Management: The manufacturer of Diclegis (doxylamine/pyridoxine), intended for use in pregnancy, specifically states that use with other CNS depressants is not recommended. Risk C: Monitor therapy
Dronabinol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dronabinol. Risk C: Monitor therapy
Dronedarone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dronedarone. Risk X: Avoid combination
Droperidol: May enhance the CNS depressant effect of CNS Depressants. Management: Consider dose reductions of droperidol or of other CNS agents (eg, opioids, barbiturates) with concomitant use. Risk D: Consider therapy modification
Duvelisib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Duvelisib. Risk X: Avoid combination
Dydrogesterone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dydrogesterone. Risk C: Monitor therapy
Ebastine: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Ebastine. CYP3A4 Inducers (Strong) may decrease the serum concentration of Ebastine. Risk C: Monitor therapy
Efavirenz: CYP3A4 Inducers (Strong) may decrease the serum concentration of Efavirenz. Risk C: Monitor therapy
Elagolix: CYP3A4 Inducers (Strong) may decrease the serum concentration of Elagolix. Risk C: Monitor therapy
Elagolix, Estradiol, and Norethindrone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Elagolix, Estradiol, and Norethindrone. Risk C: Monitor therapy
Elbasvir and Grazoprevir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Elbasvir and Grazoprevir. Risk X: Avoid combination
Elexacaftor, Tezacaftor, and Ivacaftor: CYP3A4 Inducers (Strong) may decrease the serum concentration of Elexacaftor, Tezacaftor, and Ivacaftor. Risk X: Avoid combination
Eliglustat: CYP3A4 Inducers (Strong) may decrease the serum concentration of Eliglustat. Risk X: Avoid combination
Elvitegravir: Primidone may decrease the serum concentration of Elvitegravir. Risk X: Avoid combination
Encorafenib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Encorafenib. Risk X: Avoid combination
Enfortumab Vedotin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Enfortumab Vedotin. Specifically, concentrations of the active monomethyl auristatin E (MMAE) component may be decreased. Risk C: Monitor therapy
Entrectinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Entrectinib. Risk X: Avoid combination
Enzalutamide: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Enzalutamide. CYP3A4 Inducers (Strong) may decrease the serum concentration of Enzalutamide. Management: Consider using an alternative agent that has no or minimal CYP3A4 induction potential when possible. If this combination cannot be avoided, increase the dose of enzalutamide from 160 mg daily to 240 mg daily. Risk D: Consider therapy modification
Eplerenone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Eplerenone. Risk C: Monitor therapy
Eravacycline: CYP3A4 Inducers (Strong) may decrease the serum concentration of Eravacycline. Management: Increase the eravacycline dose to 1.5 mg/kg every 12 hours when combined with strong CYP3A4 inducers. Risk D: Consider therapy modification
Erdafitinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Erdafitinib. Risk X: Avoid combination
Erlotinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Erlotinib. Management: Avoid the combination of erlotinib and strong CYP3A4 inducers whenever possible. If this combination must be used, increase erlotinib dose by 50 mg increments every 2 weeks as tolerated, to a maximum of 450 mg/day. Risk D: Consider therapy modification
Escitalopram: CYP3A4 Inducers (Strong) may decrease the serum concentration of Escitalopram. Risk C: Monitor therapy
Esketamine: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Eslicarbazepine: Primidone may decrease the serum concentration of Eslicarbazepine. (based on studies with phenobarbital) Risk C: Monitor therapy
Estazolam: CYP3A4 Inducers (Strong) may decrease the serum concentration of Estazolam. Risk C: Monitor therapy
Estrogen Derivatives: CYP3A4 Inducers (Strong) may decrease the serum concentration of Estrogen Derivatives. Risk C: Monitor therapy
Eszopiclone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Eszopiclone. Risk C: Monitor therapy
Ethosuximide: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ethosuximide. Risk C: Monitor therapy
Etizolam: CYP3A4 Inducers (Strong) may decrease the serum concentration of Etizolam. Risk C: Monitor therapy
Etoposide: CYP3A4 Inducers (Strong) may decrease the serum concentration of Etoposide. Management: When possible, seek alternatives to strong CYP3A4-inducing medications in patients receiving etoposide. If combined, monitor patients closely for diminished etoposide response and need for etoposide dose increases. Risk D: Consider therapy modification
Etoposide Phosphate: CYP3A4 Inducers (Strong) may decrease the serum concentration of Etoposide Phosphate. Management: When possible, seek alternatives to strong CYP3A4-inducing medications in patients receiving etoposide phosphate. If these combinations cannot be avoided, monitor patients closely for diminished etoposide phosphate response. Risk D: Consider therapy modification
Etoricoxib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Etoricoxib. Risk C: Monitor therapy
Etravirine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Etravirine. Risk X: Avoid combination
Everolimus: CYP3A4 Inducers (Strong) may decrease the serum concentration of Everolimus. Management: Avoid concurrent use of strong CYP3A4 inducers if possible. If coadministration cannot be avoided, monitor for decreased everolimus serum concentrations and effects, and adjust everolimus dose as needed. Risk D: Consider therapy modification
Evogliptin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Evogliptin. Risk C: Monitor therapy
Exemestane: CYP3A4 Inducers (Strong) may decrease the serum concentration of Exemestane. Management: Increase the exemestane dose to 50 mg once daily in patients receiving concurrent strong CYP3A4 inducers. Monitor patients closely for evidence of toxicity or inadequate clinical response. Risk D: Consider therapy modification
Fedratinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Fedratinib. Risk X: Avoid combination
Felbamate: May increase serum concentrations of the active metabolite(s) of Primidone. Specifically, phenobarbital concentrations may increase. Primidone may decrease the serum concentration of Felbamate. Management: Initiate felbamate at typical doses (1,200 mg/day in 3 or 4 divided doses for adults and children 14 years of age or older; 15 mg/kg/day in 3 or 4 divided doses in children 2 to 14 years of age) while reducing the primidone dose by 20%. Risk D: Consider therapy modification
Felodipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Felodipine. Management: Consider alternatives to this combination when possible. If combined, monitor for reduced felodipine efficacy and the need for felodipine dose increases. Risk D: Consider therapy modification
FentaNYL: Primidone may enhance the CNS depressant effect of FentaNYL. Primidone may decrease the serum concentration of FentaNYL. Management: Avoid use of fentanyl and primidone when possible. Monitor for respiratory depression/sedation. Because primidone is also a strong CYP3A4 inducer, monitor for decreased fentanyl efficacy and withdrawal if combined. Risk D: Consider therapy modification
Fesoterodine: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Fesoterodine. Risk C: Monitor therapy
Fexinidazole: CYP3A4 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Fexinidazole. Risk X: Avoid combination
Finerenone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Finerenone. Risk X: Avoid combination
Flibanserin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Flibanserin. Risk X: Avoid combination
Flunitrazepam: CNS Depressants may enhance the CNS depressant effect of Flunitrazepam. Management: Reduce the dose of CNS depressants when combined with flunitrazepam and monitor patients for evidence of CNS depression (eg, sedation, respiratory depression). Use non-CNS depressant alternatives when available. Risk D: Consider therapy modification
Folic Acid: May decrease the serum concentration of Primidone. Additionally, folic acid may decrease concentrations of active metabolites of primidone (e.g., phenobarbital). Risk C: Monitor therapy
Fosamprenavir: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Fosamprenavir. Risk C: Monitor therapy
Fosaprepitant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Fosaprepitant. Specifically, CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite aprepitant. Risk X: Avoid combination
Fosnetupitant: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Fosnetupitant. Risk X: Avoid combination
Fosphenytoin: May increase the metabolism of Primidone. The ratio of primidone:phenobarbital is thus changed. Risk C: Monitor therapy
Fostamatinib: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Fostamatinib. Risk X: Avoid combination
Fostemsavir: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Fostemsavir. Risk X: Avoid combination
Gefitinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Gefitinib. Management: In the absence of severe adverse reactions, increase the gefitinib dose to 500 mg daily in patients receiving strong CYP3A4 inducers; resume 250 mg dose 7 days after discontinuation of the strong inducer. Carefully monitor clinical response. Risk D: Consider therapy modification
Gemigliptin: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Gemigliptin. CYP3A4 Inducers (Strong) may decrease the serum concentration of Gemigliptin. Risk X: Avoid combination
Gestrinone: Primidone may decrease the serum concentration of Gestrinone. Risk C: Monitor therapy
Gilteritinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Gilteritinib. Risk C: Monitor therapy
Glasdegib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Glasdegib. Risk X: Avoid combination
Glecaprevir and Pibrentasvir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Glecaprevir and Pibrentasvir. Risk C: Monitor therapy
Griseofulvin: Barbiturates may decrease the serum concentration of Griseofulvin. Risk C: Monitor therapy
GuanFACINE: CYP3A4 Inducers (Strong) may decrease the serum concentration of GuanFACINE. Management: Increase extended-release guanfacine dose by up to double when initiating guanfacine in patients taking CYP3A4 inducers or if initiating a CYP3A4 inducer in a patient already taking extended-release guanfacine. Monitor for reduced guanfacine efficacy. Risk D: Consider therapy modification
Haloperidol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Haloperidol. Risk C: Monitor therapy
Hemin: Barbiturates may diminish the therapeutic effect of Hemin. Risk X: Avoid combination
Hormonal Contraceptives: CYP3A4 Inducers (Strong) may decrease the serum concentration of Hormonal Contraceptives. Management: Advise patients to use an alternative method of contraception or a back-up method during coadministration, and to continue back-up contraception for 28 days after discontinuing a strong CYP3A4 inducer to ensure contraceptive reliability. Risk D: Consider therapy modification
HYDROcodone: Primidone may enhance the CNS depressant effect of HYDROcodone. Primidone may decrease the serum concentration of HYDROcodone. Management: Avoid use of hydrocodone and primidone when possible. Monitor for respiratory depression/sedation. Because primidone is also a strong CYP3A4 inducer, monitor for decreased hydrocodone efficacy and withdrawal if combined. Risk D: Consider therapy modification
Hydrocortisone (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Hydrocortisone (Systemic). Risk C: Monitor therapy
HydrOXYzine: May enhance the CNS depressant effect of Barbiturates. Management: Consider a decrease in the barbiturate dose, as appropriate, when used together with hydroxyzine. With concurrent use, monitor patients closely for excessive response to the combination. Risk D: Consider therapy modification
Ibrexafungerp: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ibrexafungerp. Risk X: Avoid combination
Ibrutinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ibrutinib. Risk X: Avoid combination
Idelalisib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Idelalisib. Risk X: Avoid combination
Ifosfamide: CYP3A4 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Ifosfamide. CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Ifosfamide. Risk C: Monitor therapy
Imatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Imatinib. Management: Avoid use of imatinib and strong CYP3A4 inducers when possible. If such a combination must be used, increase imatinib dose by at least 50% and monitor the patient's clinical response closely. Doses up to 1200 mg/day (600 mg twice daily) have been used. Risk D: Consider therapy modification
Indinavir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Indinavir. Management: Consider avoiding the combination of indinavir and strong CYP3A4 inducers whenever possible due to the risk for decreased indinavir concentrations, reduced efficacy, and development of resistance. If combined, monitor for indinavir treatment failure Risk D: Consider therapy modification
Infigratinib: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Infigratinib. CYP3A4 Inducers (Strong) may decrease the serum concentration of Infigratinib. Risk X: Avoid combination
Irinotecan Products: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Irinotecan Products. Specifically, serum concentrations of SN-38 may be reduced. CYP3A4 Inducers (Strong) may decrease the serum concentration of Irinotecan Products. Management: Avoid administration of strong CYP3A4 inducers during irinotecan treatment, and substitute non-CYP3A4 inducing agents at least 2 weeks prior to irinotecan initiation, whenever possible. If combined, monitor for reduced irinotecan efficacy. Risk D: Consider therapy modification
Isavuconazonium Sulfate: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Isavuconazonium Sulfate. Specifically, CYP3A4 Inducers (Strong) may decrease isavuconazole serum concentrations. Risk X: Avoid combination
Isradipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Isradipine. Risk C: Monitor therapy
Istradefylline: CYP3A4 Inducers (Strong) may decrease the serum concentration of Istradefylline. Risk X: Avoid combination
Itraconazole: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Itraconazole. CYP3A4 Inducers (Strong) may decrease the serum concentration of Itraconazole. Risk X: Avoid combination
Ivabradine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ivabradine. Risk X: Avoid combination
Ivacaftor: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ivacaftor. Risk X: Avoid combination
Ivosidenib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ivosidenib. Risk X: Avoid combination
Ixabepilone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ixabepilone. Management: Avoid this combination whenever possible. If this combination must be used, a gradual increase in ixabepilone dose from 40 mg/m2 to 60 mg/m2 (given as a 4-hour infusion), as tolerated, should be considered. Risk D: Consider therapy modification
Ixazomib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ixazomib. Risk X: Avoid combination
Kava Kava: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Ketamine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ketamine. Risk C: Monitor therapy
Ketoconazole (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Ketoconazole (Systemic). Management: The use of ketoconazole concurrently with or within 2 weeks of a strong CYP3A4 inducer is not recommended. If such a combination cannot be avoided, monitor patients closely for evidence of diminished clinical response to ketoconazole. Risk D: Consider therapy modification
Kratom: May enhance the CNS depressant effect of CNS Depressants. Risk X: Avoid combination
Lacidipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lacidipine. Risk C: Monitor therapy
LamoTRIgine: May enhance the adverse/toxic effect of Primidone. Specifically, the risk for hematologic toxicities may be increased. Primidone may decrease the serum concentration of LamoTRIgine. Management: For patients taking primidone without valproate, lamotrigine dose adjustments are recommended for lamotrigine initiation. Recommendations vary based on lamotrigine indication and age. See full interact monograph for details. Risk D: Consider therapy modification
Lapatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lapatinib. Management: If concomitant use cannot be avoided, titrate lapatinib gradually from 1,250 mg/day up to 4,500 mg/day (HER2 positive metastatic breast cancer) or 1,500 mg/day up to 5,500 mg/day (hormone receptor/HER2 positive breast cancer) as tolerated. Risk D: Consider therapy modification
Larotrectinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Larotrectinib. Management: Avoid use of strong CYP3A4 inducers with larotrectinib. If this combination cannot be avoided, double the larotrectinib dose. Reduced to previous dose after stopping the inducer after a period of 3 to 5 times the inducer's half-life. Risk D: Consider therapy modification
Ledipasvir: Primidone may decrease the serum concentration of Ledipasvir. Risk X: Avoid combination
Lefamulin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lefamulin. Management: Avoid concomitant use of lefamulin with strong CYP3A4 inducers unless the benefits outweigh the risks. Risk D: Consider therapy modification
Lefamulin (Intravenous): CYP3A4 Inducers (Strong) may decrease the serum concentration of Lefamulin (Intravenous). Management: Avoid concomitant use of lefamulin intravenous infusion with strong CYP3A4 inducers unless the benefits outweigh the risks. Risk D: Consider therapy modification
Lemborexant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lemborexant. Risk X: Avoid combination
Lercanidipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lercanidipine. Risk C: Monitor therapy
Letermovir: May increase the serum concentration of UGT1A1 Inducers. Risk X: Avoid combination
Leucovorin Calcium-Levoleucovorin: May decrease the serum concentration of Primidone. Additionally, leucovorin/levoleucovorin may decrease concentrations of active metabolites of primidone (e.g., phenobarbital). Risk C: Monitor therapy
Leuprolide and Norethindrone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Leuprolide and Norethindrone. Specifically, norethindrone concentrations may be decreased. Risk C: Monitor therapy
Levamlodipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Levamlodipine. Risk C: Monitor therapy
LevETIRAcetam: May enhance the CNS depressant effect of Primidone. Primidone may decrease the serum concentration of LevETIRAcetam. Risk C: Monitor therapy
Levoketoconazole: CYP3A4 Inducers (Strong) may decrease the serum concentration of Levoketoconazole. Risk X: Avoid combination
Levomefolate: May decrease serum concentrations of the active metabolite(s) of Primidone. Levomefolate may decrease the serum concentration of Primidone. Risk C: Monitor therapy
Levomethadone: May enhance the CNS depressant effect of Primidone. Primidone may decrease the serum concentration of Levomethadone. Management: Avoid concomitant use of levomethadone and primidone when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Risk D: Consider therapy modification
Levonorgestrel (IUD): CYP3A4 Inducers (Strong) may diminish the therapeutic effect of Levonorgestrel (IUD). CYP3A4 Inducers (Strong) may decrease the serum concentration of Levonorgestrel (IUD). Risk C: Monitor therapy
Lidocaine (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Lidocaine (Systemic). Risk C: Monitor therapy
LinaGLIPtin: CYP3A4 Inducers (Strong) may decrease the serum concentration of LinaGLIPtin. Management: Strongly consider using an alternative to any strong CYP3A4 inducer in patients who are being treated with linagliptin. If this combination is used, monitor patients closely for evidence of reduced linagliptin effectiveness. Risk D: Consider therapy modification
Lisuride: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Lofexidine: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Lonafarnib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lonafarnib. Risk X: Avoid combination
Lopinavir: Primidone may decrease the serum concentration of Lopinavir. Management: Avoid once-daily administration of lopinavir/ritonavir if used together with phenobarbital. If lopinavir/ritonavir twice daily is combined with phenobarbital, monitor closely for decreased efficacy of lopinavir/ritonavir. Risk D: Consider therapy modification
Lorlatinib: CYP3A4 Inducers (Strong) may enhance the hepatotoxic effect of Lorlatinib. CYP3A4 Inducers (Strong) may decrease the serum concentration of Lorlatinib. Risk X: Avoid combination
Lumacaftor and Ivacaftor: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lumacaftor and Ivacaftor. Specifically, the serum concentration of ivacaftor may be decreased. Risk X: Avoid combination
Lumateperone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lumateperone. Risk X: Avoid combination
Lurasidone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lurasidone. Risk X: Avoid combination
Lurbinectedin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lurbinectedin. Risk X: Avoid combination
Macimorelin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Macimorelin. Risk X: Avoid combination
Macitentan: CYP3A4 Inducers (Strong) may decrease the serum concentration of Macitentan. Risk X: Avoid combination
Magnesium Sulfate: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Manidipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Manidipine. Management: Consider avoiding concomitant use of manidipine and strong CYP3A4 inducers. If combined, monitor closely for decreased manidipine effects and loss of efficacy. Increased manidipine doses may be required. Risk D: Consider therapy modification
Maraviroc: CYP3A4 Inducers (Strong) may decrease the serum concentration of Maraviroc. Management: Increase maraviroc adult dose to 600 mg twice/day, but only if not receiving a strong CYP3A4 inhibitor. Not recommended for pediatric patients not also receiving a strong CYP3A4 inhibitor. Contraindicated in patients with CrCl less than 30 mL/min. Risk D: Consider therapy modification
Maribavir: Primidone may decrease the serum concentration of Maribavir. Management: Increase the dose of maribavir to 1,200 mg twice daily with concomitant use of primidone. Risk D: Consider therapy modification
Mefloquine: May diminish the therapeutic effect of Primidone. Primidone may decrease the serum concentration of Mefloquine. Mefloquine may decrease the serum concentration of Primidone. Management: Mefloquine is contraindicated for malaria prophylaxis in persons with a history of seizures. If primidone is being used for another indication, monitor for decreased concentrations and efficacy of both primidone/phenobarbital and mefloquine. Risk D: Consider therapy modification
Meperidine: Primidone may enhance the CNS depressant effect of Meperidine. Primidone may increase serum concentrations of the active metabolite(s) of Meperidine. Management: Avoid concomitant use of meperidine and primidone when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Risk D: Consider therapy modification
Methadone: Primidone may enhance the CNS depressant effect of Methadone. Primidone may decrease the serum concentration of Methadone. Management: Avoid concomitant use of methadone and primidone when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Risk D: Consider therapy modification
Methotrimeprazine: CNS Depressants may enhance the CNS depressant effect of Methotrimeprazine. Methotrimeprazine may enhance the CNS depressant effect of CNS Depressants. Management: Reduce the usual dose of CNS depressants by 50% if starting methotrimeprazine until the dose of methotrimeprazine is stable. Monitor patient closely for evidence of CNS depression. Risk D: Consider therapy modification
Methoxyflurane: Barbiturates may enhance the nephrotoxic effect of Methoxyflurane. Barbiturates may increase the metabolism of Methoxyflurane. Risk X: Avoid combination
Methylergonovine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Methylergonovine. Risk C: Monitor therapy
Methylfolate: May decrease the serum concentration of Primidone. Risk C: Monitor therapy
Methylphenidate: May increase serum concentrations of the active metabolite(s) of Primidone. Specifically, phenobarbital concentrations could become elevated. Methylphenidate may increase the serum concentration of Primidone. Risk C: Monitor therapy
MethylPREDNISolone: CYP3A4 Inducers (Strong) may decrease the serum concentration of MethylPREDNISolone. Management: Consider methylprednisolone dose increases in patients receiving strong CYP3A4 inducers and monitor closely for reduced steroid efficacy. Risk D: Consider therapy modification
Metoclopramide: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
MetroNIDAZOLE (Systemic): Primidone may decrease the serum concentration of MetroNIDAZOLE (Systemic). Risk C: Monitor therapy
MetyroSINE: CNS Depressants may enhance the sedative effect of MetyroSINE. Risk C: Monitor therapy
Mianserin: May enhance the CNS depressant effect of Barbiturates. Mianserin may diminish the therapeutic effect of Barbiturates. Barbiturates may decrease the serum concentration of Mianserin. Risk X: Avoid combination
Midazolam: CYP3A4 Inducers (Strong) may decrease the serum concentration of Midazolam. Risk C: Monitor therapy
Midostaurin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Midostaurin. Risk X: Avoid combination
MiFEPRIStone: CYP3A4 Inducers (Strong) may decrease the serum concentration of MiFEPRIStone. Risk X: Avoid combination
Minocycline (Systemic): May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Mirabegron: CYP3A4 Inducers (Strong) may decrease the serum concentration of Mirabegron. Risk C: Monitor therapy
Mirodenafil: CYP3A4 Inducers (Strong) may decrease the serum concentration of Mirodenafil. Management: Consider avoiding the concomitant use of mirodenafil and strong CYP3A4 inducers. If combined, monitor for decreased mirodenafil effects. Mirodenafil dose increases may be required to achieve desired effects. Risk D: Consider therapy modification
Mirtazapine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Mirtazapine. Risk C: Monitor therapy
Mitapivat: CYP3A4 Inducers (Strong) may decrease the serum concentration of Mitapivat. Risk X: Avoid combination
Mobocertinib: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Mobocertinib. CYP3A4 Inducers (Strong) may decrease the serum concentration of Mobocertinib. Risk X: Avoid combination
Multivitamins/Minerals (with ADEK, Folate, Iron): May decrease the serum concentration of Barbiturates. Risk C: Monitor therapy
Naldemedine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Naldemedine. Risk X: Avoid combination
Naloxegol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Naloxegol. Risk X: Avoid combination
Nateglinide: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nateglinide. Risk C: Monitor therapy
Nelfinavir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nelfinavir. Risk C: Monitor therapy
Neratinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Neratinib. Risk X: Avoid combination
Netupitant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Netupitant. Risk X: Avoid combination
Nevirapine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nevirapine. Management: Consider alternatives to this combination when possible. If combined, monitor for reduced nevirapine efficacy. Risk D: Consider therapy modification
NiCARdipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of NiCARdipine. Risk C: Monitor therapy
NIFEdipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of NIFEdipine. Management: Avoid coadministration of nifedipine with strong CYP3A4 inducers when possible and if combined, monitor patients closely for clinical signs of diminished nifedipine response. Risk D: Consider therapy modification
Nilotinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nilotinib. Risk X: Avoid combination
Nilvadipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nilvadipine. Risk C: Monitor therapy
NiMODipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of NiMODipine. Risk X: Avoid combination
Nintedanib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nintedanib. Risk C: Monitor therapy
Nirmatrelvir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nirmatrelvir. Risk X: Avoid combination
Nisoldipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nisoldipine. Risk X: Avoid combination
Nitrendipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nitrendipine. Risk C: Monitor therapy
OLANZapine: CYP1A2 Inducers (Weak) may decrease the serum concentration of OLANZapine. Risk C: Monitor therapy
Olaparib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Olaparib. Risk X: Avoid combination
Olmutinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Olmutinib. Risk C: Monitor therapy
Olopatadine (Nasal): May enhance the CNS depressant effect of CNS Depressants. Risk X: Avoid combination
Ondansetron: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ondansetron. Risk C: Monitor therapy
Opioid Agonists: CNS Depressants may enhance the CNS depressant effect of Opioid Agonists. Management: Avoid concomitant use of opioid agonists and benzodiazepines or other CNS depressants when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Risk D: Consider therapy modification
Orlistat: May decrease the serum concentration of Antiseizure Agents. Risk C: Monitor therapy
Orphenadrine: CNS Depressants may enhance the CNS depressant effect of Orphenadrine. Risk X: Avoid combination
Osilodrostat: CYP3A4 Inducers (Strong) may decrease the serum concentration of Osilodrostat. Risk C: Monitor therapy
Osimertinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Osimertinib. Management: Avoid coadministration of osimertinib and strong CYP3A4 inducers if possible. If coadministration is unavoidable, increase osimertinib to 160 mg daily. Reduce osimertinib to 80 mg daily 3 weeks after discontinuation of the strong CYP3A4 inducer. Risk D: Consider therapy modification
OXcarbazepine: CYP3A4 Inducers (Strong) may decrease the serum concentration of OXcarbazepine. Specifically, the concentrations of the 10-monohydroxy active metabolite of oxcarbazepine may be decreased. Risk C: Monitor therapy
Oxomemazine: May enhance the CNS depressant effect of CNS Depressants. Risk X: Avoid combination
Oxybate Salt Products: CNS Depressants may enhance the CNS depressant effect of Oxybate Salt Products. Management: Consider alternatives to this combination when possible. If combined, dose reduction or discontinuation of one or more CNS depressants (including the oxybate salt product) should be considered. Interrupt oxybate salt treatment during short-term opioid use Risk D: Consider therapy modification
OxyCODONE: Primidone may enhance the CNS depressant effect of OxyCODONE. Primidone may decrease the serum concentration of OxyCODONE. Management: Avoid use of oxycodone and primidone when possible. Monitor for respiratory depression/sedation. Because primidone is also a strong CYP3A4 inducer, monitor for decreased oxycodone efficacy and withdrawal if combined. Risk D: Consider therapy modification
PACLitaxel (Conventional): CYP3A4 Inducers (Strong) may decrease the serum concentration of PACLitaxel (Conventional). Risk C: Monitor therapy
PACLitaxel (Protein Bound): CYP3A4 Inducers (Strong) may decrease the serum concentration of PACLitaxel (Protein Bound). Risk C: Monitor therapy
Palbociclib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Palbociclib. Risk X: Avoid combination
Panobinostat: CYP3A4 Inducers (Strong) may decrease the serum concentration of Panobinostat. Risk X: Avoid combination
Paraldehyde: CNS Depressants may enhance the CNS depressant effect of Paraldehyde. Risk X: Avoid combination
PAZOPanib: CYP3A4 Inducers (Strong) may decrease the serum concentration of PAZOPanib. Risk X: Avoid combination
Pemigatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Pemigatinib. Risk X: Avoid combination
Perampanel: CYP3A4 Inducers (Strong) may decrease the serum concentration of Perampanel. Management: Increase perampanel starting dose to 4 mg/day if used with strong CYP3A4 inducers. Increase perampanel dose by 2 mg/day no more than once weekly based on response and tolerability. Dose adjustments may be needed if the inducer is discontinued. Risk D: Consider therapy modification
Pexidartinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Pexidartinib. Risk X: Avoid combination
Phenytoin: May increase the metabolism of Primidone. The ratio of primidone:phenobarbital is thus changed. Risk C: Monitor therapy
Pimavanserin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Pimavanserin. Risk X: Avoid combination
Piperaquine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Piperaquine. Risk X: Avoid combination
Piribedil: CNS Depressants may enhance the CNS depressant effect of Piribedil. Risk C: Monitor therapy
Pitolisant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Pitolisant. Management: If on a stable pitolisant dose of 8.9 mg or 17.8 mg/day and starting a strong CYP3A4 inducer, double the pitolisant dose over 7 days (ie, to either 17.8 mg/day or 35.6 mg/day, respectively). Reduce pitolisant dose by 50% when the inducer is discontinued. Risk D: Consider therapy modification
Polatuzumab Vedotin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Polatuzumab Vedotin. Exposure to unconjugated MMAE, the cytotoxic small molecule component of polatuzumab vedotin, may be decreased. Risk C: Monitor therapy
PONATinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of PONATinib. Management: Avoid coadministration of ponatinib with strong CYP3A4 inducers unless the potential benefit of concomitant treatment outweighs the risk of reduced ponatinib exposure. Monitor patients for reduced ponatinib efficacy if combined. Risk D: Consider therapy modification
Ponesimod: UGT1A1 Inducers may decrease the serum concentration of Ponesimod. Risk X: Avoid combination
Pralsetinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Pralsetinib. Management: Avoid concomitant use of pralsetinib with strong CYP3A4 inducers when possible. If combined, increase the starting dose of pralsetinib to double the current pralsetinib dosage starting on day 7 of coadministration. Risk D: Consider therapy modification
Pramipexole: CNS Depressants may enhance the sedative effect of Pramipexole. Risk C: Monitor therapy
Praziquantel: CYP3A4 Inducers (Strong) may decrease the serum concentration of Praziquantel. Risk X: Avoid combination
PrednisoLONE (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of PrednisoLONE (Systemic). Risk C: Monitor therapy
PredniSONE: CYP3A4 Inducers (Strong) may decrease the serum concentration of PredniSONE. Risk C: Monitor therapy
Pretomanid: CYP3A4 Inducers (Strong) may decrease the serum concentration of Pretomanid. Risk X: Avoid combination
Propacetamol: Primidone may increase the metabolism of Propacetamol. Specifically, formation of the hepatotoxic NAPQI metabolite may be increased. Risk C: Monitor therapy
Propafenone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Propafenone. Risk C: Monitor therapy
Pyridoxine: May decrease serum concentrations of the active metabolite(s) of Primidone. Specifically, concentrations of phenobarbital may be reduced. Risk C: Monitor therapy
QUEtiapine: CYP3A4 Inducers (Strong) may decrease the serum concentration of QUEtiapine. Management: An increase in quetiapine dose (as much as 5 times the regular dose) may be required to maintain therapeutic benefit. Reduce the quetiapine dose back to the previous/regular dose within 7 to 14 days of discontinuing the inducer. Risk D: Consider therapy modification
QuiNIDine: CYP3A4 Inducers (Strong) may decrease the serum concentration of QuiNIDine. Risk C: Monitor therapy
QuiNINE: May increase the serum concentration of Primidone. Primidone may decrease the serum concentration of QuiNINE. Management: Consider alternatives to this combination when possible. If coadministration of primidone and quinine cannot be avoided, monitor for reduced quinine efficacy and for increased phenobarbital (active metabolite) serum concentrations and toxicities. Risk D: Consider therapy modification
Radotinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Radotinib. Management: Consider alternatives to this combination when possible as the risk of radotinib treatment failure may be increased. Risk D: Consider therapy modification
Ramelteon: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ramelteon. Risk C: Monitor therapy
Ranolazine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ranolazine. Risk X: Avoid combination
Reboxetine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Reboxetine. Risk C: Monitor therapy
Regorafenib: CYP3A4 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Regorafenib. CYP3A4 Inducers (Strong) may decrease the serum concentration of Regorafenib. Risk X: Avoid combination
Remdesivir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Remdesivir. Risk C: Monitor therapy
Repaglinide: CYP3A4 Inducers (Strong) may decrease the serum concentration of Repaglinide. Risk C: Monitor therapy
Ribociclib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ribociclib. Risk X: Avoid combination
Rifabutin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Rifabutin. Risk C: Monitor therapy
Rilpivirine: Primidone may decrease the serum concentration of Rilpivirine. Risk X: Avoid combination
Rimegepant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Rimegepant. Risk X: Avoid combination
Riociguat: CYP3A4 Inducers (Strong) may decrease the serum concentration of Riociguat. Risk C: Monitor therapy
Ripretinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ripretinib. Risk X: Avoid combination
RisperiDONE: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of RisperiDONE. CYP3A4 Inducers (Strong) may decrease the serum concentration of RisperiDONE. Management: Careful monitoring for reduced risperidone efficacy and possible dose adjustment are recommended when combined with strong CYP3A4 inducers. See full interaction monograph for details. Risk D: Consider therapy modification
Ritonavir: May decrease the serum concentration of Primidone. Primidone may decrease the serum concentration of Ritonavir. Management: Consider avoiding this combination due to the potential for decreased ritonavir concentrations and the possible development of resistance. If combined, monitor for decreased phenobarbital and ritonavir concentrations and effects during coadministration. Risk D: Consider therapy modification
Rivaroxaban: CYP3A4 Inducers (Strong) may decrease the serum concentration of Rivaroxaban. Management: Consider alternatives to use of rivaroxaban with strong CYP3A4 inducers. Use of a strong CYP3A4 inducer with rivaroxaban should be strictly avoided in any patient who is using an agent (either the CYP3A4 inducer or a third drug) that induces P-gp. Risk D: Consider therapy modification
Roflumilast: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Roflumilast. CYP3A4 Inducers (Strong) may decrease the serum concentration of Roflumilast. Risk X: Avoid combination
Rolapitant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Rolapitant. Risk X: Avoid combination
RomiDEPsin: CYP3A4 Inducers (Strong) may decrease the serum concentration of RomiDEPsin. Risk X: Avoid combination
Ropeginterferon Alfa-2b: CNS Depressants may enhance the adverse/toxic effect of Ropeginterferon Alfa-2b. Specifically, the risk of neuropsychiatric adverse effects may be increased. Management: Avoid coadministration of ropeginterferon alfa-2b and other CNS depressants. If this combination cannot be avoided, monitor patients for neuropsychiatric adverse effects (eg, depression, suicidal ideation, aggression, mania). Risk D: Consider therapy modification
ROPINIRole: CNS Depressants may enhance the sedative effect of ROPINIRole. Risk C: Monitor therapy
Rotigotine: CNS Depressants may enhance the sedative effect of Rotigotine. Risk C: Monitor therapy
Rufinamide: May increase serum concentrations of the active metabolite(s) of Primidone. Specifically, phenobarbital concentrations may be increased. Primidone may decrease the serum concentration of Rufinamide. Risk C: Monitor therapy
Ruxolitinib (Systemic): CYP3A4 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Ruxolitinib (Systemic). CYP3A4 Inducers (Strong) may decrease the serum concentration of Ruxolitinib (Systemic). Risk C: Monitor therapy
Sacituzumab Govitecan: UGT1A1 Inducers may decrease serum concentrations of the active metabolite(s) of Sacituzumab Govitecan. Specifically, concentrations of SN-38 may be decreased. Risk X: Avoid combination
Samidorphan: CYP3A4 Inducers (Strong) may decrease the serum concentration of Samidorphan. Risk X: Avoid combination
Sapropterin: Primidone may decrease the serum concentration of Sapropterin. Risk C: Monitor therapy
Saquinavir: Primidone may decrease the serum concentration of Saquinavir. Risk X: Avoid combination
SAXagliptin: CYP3A4 Inducers (Strong) may decrease the serum concentration of SAXagliptin. Risk C: Monitor therapy
Selpercatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Selpercatinib. Risk X: Avoid combination
Selumetinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Selumetinib. Risk X: Avoid combination
Sertraline: CYP3A4 Inducers (Strong) may decrease the serum concentration of Sertraline. Risk C: Monitor therapy
Sildenafil: CYP3A4 Inducers (Strong) may decrease the serum concentration of Sildenafil. Risk C: Monitor therapy
Simeprevir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Simeprevir. Risk X: Avoid combination
Sirolimus (Conventional): CYP3A4 Inducers (Strong) may decrease the serum concentration of Sirolimus (Conventional). Management: Avoid concomitant use of strong CYP3A4 inducers and sirolimus if possible. If combined, monitor for reduced serum sirolimus concentrations. Sirolimus dose increases will likely be necessary to prevent subtherapeutic sirolimus levels. Risk D: Consider therapy modification
Sirolimus (Protein Bound): CYP3A4 Inducers (Strong) may decrease the serum concentration of Sirolimus (Protein Bound). Risk X: Avoid combination
Sofosbuvir: Primidone may decrease the serum concentration of Sofosbuvir. Risk X: Avoid combination
Solifenacin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Solifenacin. Risk C: Monitor therapy
Sonidegib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Sonidegib. Risk X: Avoid combination
SORAfenib: CYP3A4 Inducers (Strong) may decrease the serum concentration of SORAfenib. Risk X: Avoid combination
Sotorasib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Sotorasib. Risk X: Avoid combination
Stiripentol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Stiripentol. Management: Avoid concomitant use of stiripentol and strong CYP3A4 inducers when possible. If combined, monitor for reduced stiripentol efficacy and increase the stiripentol dose as needed. Risk D: Consider therapy modification
SUFentanil: Primidone may enhance the CNS depressant effect of SUFentanil. Primidone may decrease the serum concentration of SUFentanil. Management: Avoid use of sufentanil and primidone when possible. Monitor for respiratory depression/sedation. Because primidone is also a strong CYP3A4 inducer, monitor for decreased sufentanil efficacy and withdrawal if combined. Risk D: Consider therapy modification
Sulthiame: Primidone may enhance the adverse/toxic effect of Sulthiame. Risk C: Monitor therapy
SUNItinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of SUNItinib. Management: Avoid when possible. If combined, increase sunitinib dose to a max of 87.5 mg daily when treating GIST or RCC. Increase sunitinib dose to a max of 62.5 mg daily when treating PNET. Monitor patients for both reduced efficacy and increased toxicities. Risk D: Consider therapy modification
Suvorexant: CNS Depressants may enhance the CNS depressant effect of Suvorexant. Management: Dose reduction of suvorexant and/or any other CNS depressant may be necessary. Use of suvorexant with alcohol is not recommended, and the use of suvorexant with any other drug to treat insomnia is not recommended. Risk D: Consider therapy modification
Tacrolimus (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Tacrolimus (Systemic). Management: Monitor for decreased tacrolimus concentrations and effects when combined with strong CYP3A4 inducers. Tacrolimus dose increases will likely be needed during concomitant use. Risk D: Consider therapy modification
Tadalafil: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tadalafil. Management: Erectile dysfunction or benign prostatic hypertrophy: monitor for decreased effectiveness - no standard dose adjustment is recommended. Avoid use of tadalafil for pulmonary arterial hypertension in patients receiving a strong CYP3A4 inducer. Risk D: Consider therapy modification
Tamoxifen: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Tamoxifen. CYP3A4 Inducers (Strong) may decrease the serum concentration of Tamoxifen. Risk X: Avoid combination
Tasimelteon: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tasimelteon. Risk X: Avoid combination
Tazemetostat: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tazemetostat. Risk X: Avoid combination
Telithromycin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Telithromycin. Risk X: Avoid combination
Temsirolimus: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Temsirolimus. Specifically, concentrations of sirolimus may be decreased. CYP3A4 Inducers (Strong) may decrease the serum concentration of Temsirolimus. Management: Avoid concomitant use of temsirolimus and strong CYP3A4 inducers. If coadministration is unavoidable, increase temsirolimus dose to 50 mg per week. Resume previous temsirolimus dose after discontinuation of the strong CYP3A4 inducer. Risk D: Consider therapy modification
Teniposide: CYP3A4 Inducers (Strong) may decrease the serum concentration of Teniposide. Risk C: Monitor therapy
Tenofovir Alafenamide: Primidone may decrease the serum concentration of Tenofovir Alafenamide. Risk X: Avoid combination
Tepotinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tepotinib. Risk X: Avoid combination
Tetrahydrocannabinol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tetrahydrocannabinol. Risk C: Monitor therapy
Tetrahydrocannabinol and Cannabidiol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tetrahydrocannabinol and Cannabidiol. Management: Avoid use of the tetrahydrocannabinol/cannabidiol oromucosal spray and strong CYP3A4 inducers when possible. If combined use is necessary, careful titration is recommended, notably within the two weeks following discontinuation of the inducer. Risk D: Consider therapy modification
Tezacaftor and Ivacaftor: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tezacaftor and Ivacaftor. Risk X: Avoid combination
Thalidomide: CNS Depressants may enhance the CNS depressant effect of Thalidomide. Risk X: Avoid combination
Theophylline Derivatives: Barbiturates may decrease the serum concentration of Theophylline Derivatives. Risk C: Monitor therapy
Thiotepa: CYP3A4 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Thiotepa. CYP3A4 Inducers (Strong) may decrease the serum concentration of Thiotepa. Management: Thiotepa prescribing information recommends avoiding concomitant use of thiotepa and strong CYP3A4 inducers. If concomitant use is unavoidable, monitor for adverse effects. Risk D: Consider therapy modification
Thiothixene: Primidone may decrease the serum concentration of Thiothixene. Risk C: Monitor therapy
Thyroid Products: Primidone may decrease the serum concentration of Thyroid Products. Risk C: Monitor therapy
TiaGABine: CYP3A4 Inducers (Strong) may decrease the serum concentration of TiaGABine. Risk C: Monitor therapy
Ticagrelor: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Ticagrelor. CYP3A4 Inducers (Strong) may decrease the serum concentration of Ticagrelor. Risk X: Avoid combination
Tipranavir: Primidone may decrease the serum concentration of Tipranavir. Tipranavir may decrease the serum concentration of Primidone. Risk C: Monitor therapy
Tivozanib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tivozanib. Risk X: Avoid combination
Tofacitinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tofacitinib. Risk X: Avoid combination
Tolvaptan: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tolvaptan. Risk X: Avoid combination
Toremifene: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Toremifene. CYP3A4 Inducers (Strong) may decrease the serum concentration of Toremifene. Risk X: Avoid combination
Trabectedin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Trabectedin. Risk X: Avoid combination
TraMADol: Primidone may enhance the CNS depressant effect of TraMADol. Primidone may decrease the serum concentration of TraMADol. Management: Avoid use of tramadol and primidone when possible. Monitor for respiratory depression/sedation. Because primidone is also a strong CYP3A4 inducer, monitor for decreased tramadol efficacy and withdrawal if combined. Risk D: Consider therapy modification
TraZODone: CYP3A4 Inducers (Strong) may decrease the serum concentration of TraZODone. Management: Consider increasing the trazodone dose during coadministration with strong CYP3A4 inducers. Risk D: Consider therapy modification
Triamcinolone (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Triamcinolone (Systemic). Risk C: Monitor therapy
Triazolam: CYP3A4 Inducers (Strong) may decrease the serum concentration of Triazolam. Management: Consider alternatives to this combination when possible. If combined, monitor for reduced triazolam efficacy. Substantial triazolam dose increases will likely be required. Risk D: Consider therapy modification
Tricyclic Antidepressants: Barbiturates may increase the metabolism of Tricyclic Antidepressants. Management: Monitor for decreased efficacy of tricyclic antidepressants if a barbiturate is initiated/dose increased, or increased effects if a barbiturate is discontinued/dose decreased. Tricyclic antidepressant dose adjustments are likely required. Risk D: Consider therapy modification
Trimeprazine: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Tropisetron: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tropisetron. Risk C: Monitor therapy
Tucatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tucatinib. Risk X: Avoid combination
Ubrogepant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ubrogepant. Risk X: Avoid combination
Udenafil: CYP3A4 Inducers (Strong) may decrease the serum concentration of Udenafil. Risk C: Monitor therapy
Ulipristal: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ulipristal. Risk X: Avoid combination
Upadacitinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Upadacitinib. Risk X: Avoid combination
Valbenazine: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Valbenazine. CYP3A4 Inducers (Strong) may decrease the serum concentration of Valbenazine. Risk X: Avoid combination
Valerian: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Valproate Products: May increase the serum concentration of Primidone. More specifically, the serum concentration of phenobarbital, primidone's primary active metabolite, may be increased. Primidone may decrease the serum concentration of Valproate Products. Risk C: Monitor therapy
Vandetanib: CYP3A4 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Vandetanib. CYP3A4 Inducers (Strong) may decrease the serum concentration of Vandetanib. Risk X: Avoid combination
Velpatasvir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Velpatasvir. Risk X: Avoid combination
Vemurafenib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vemurafenib. Management: Avoid coadministration of vemurafenib and strong CYP3A4 inducers if possible. If coadministration is unavoidable, increase the vemurafenib dose by 240 mg as tolerated. Resume prior vemurafenib dose 2 weeks after discontinuation of strong CYP3A4 inducer. Risk D: Consider therapy modification
Venetoclax: CYP3A4 Inducers (Strong) may decrease the serum concentration of Venetoclax. Risk X: Avoid combination
Verapamil: CYP3A4 Inducers (Strong) may decrease the serum concentration of Verapamil. Management: Consider alternatives to this combination. If combined, monitor for reduced verapamil efficacy. Verapamil dose increases may be necessary. Risk D: Consider therapy modification
Vilazodone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vilazodone. Management: Consider increasing vilazodone dose by as much as 2-fold (do not exceed 80 mg/day), based on response, in patients receiving strong CYP3A4 inducers for > 14 days. Reduce to the original vilazodone dose over 1 to 2 weeks after inducer discontinuation. Risk D: Consider therapy modification
VinCRIStine: CYP3A4 Inducers (Strong) may decrease the serum concentration of VinCRIStine. Risk C: Monitor therapy
VinCRIStine (Liposomal): CYP3A4 Inducers (Strong) may decrease the serum concentration of VinCRIStine (Liposomal). Risk X: Avoid combination
Vinflunine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vinflunine. Risk X: Avoid combination
Vinorelbine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vinorelbine. Risk C: Monitor therapy
Vitamin K Antagonists (eg, warfarin): Barbiturates may increase the metabolism of Vitamin K Antagonists. Management: Monitor INR more closely. Anticoagulant dose increases of 30% to 60% may be needed after a barbiturate is initiated or given at an increased dose. Anticoagulant dose decreases may be needed following barbiturate discontinuation or dose reduction. Risk D: Consider therapy modification
Voclosporin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Voclosporin. Risk X: Avoid combination
Vorapaxar: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vorapaxar. Risk X: Avoid combination
Voriconazole: Primidone may decrease the serum concentration of Voriconazole. Risk X: Avoid combination
Vortioxetine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vortioxetine. Management: Consider increasing the vortioxetine dose to no more than 3 times the original dose when used with a strong drug metabolism inducer for more than 14 days. The vortioxetine dose should be returned to normal within 14 days of stopping the strong inducer. Risk D: Consider therapy modification
Voxelotor: CYP3A4 Inducers (Strong) may decrease the serum concentration of Voxelotor. Management: Avoid concomitant use of voxelotor and strong CYP3A4 inducers. If unavoidable, increase the voxelotor dose to 2,500 mg once daily. For children ages 4 to less than 12 years, weight-based dose adjustments are required. See full monograph for details. Risk D: Consider therapy modification
Voxilaprevir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Voxilaprevir. Risk X: Avoid combination
Zaleplon: CYP3A4 Inducers (Strong) may decrease the serum concentration of Zaleplon. Management: Consider the use of an alternative hypnotic that is not metabolized by CYP3A4 in patients receiving strong CYP3A4 inducers. If zaleplon is combined with a strong CYP3A4 inducer, monitor for decreased effectiveness of zaleplon. Risk D: Consider therapy modification
Zanubrutinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Zanubrutinib. Risk X: Avoid combination
Zolpidem: CNS Depressants may enhance the CNS depressant effect of Zolpidem. Management: Reduce the Intermezzo brand sublingual zolpidem adult dose to 1.75 mg for men who are also receiving other CNS depressants. No such dose change is recommended for women. Avoid use with other CNS depressants at bedtime; avoid use with alcohol. Risk D: Consider therapy modification
Zonisamide: May enhance the CNS depressant effect of Primidone. Primidone may decrease the serum concentration of Zonisamide. Risk C: Monitor therapy
Zopiclone: Primidone may enhance the CNS depressant effect of Zopiclone. Primidone may decrease the serum concentration of Zopiclone. Risk C: Monitor therapy
Zuclopenthixol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Zuclopenthixol. Risk C: Monitor therapy
Protein-deficient diets increase duration of action of primidone.
Folic acid: Low erythrocyte and CSF folate concentrations. Megaloblastic anemia has been reported. To avoid folic acid deficiency and megaloblastic anemia, some clinicians recommend giving patients on antiseizure medications prophylactic doses of folic acid and cyanocobalamin.
Vitamin B: Primidone use has been associated with low serum concentrations of vitamin B2 (riboflavin), B6 (pyridoxine), and B12 (cyanocobalamin), which may contribute to hyperhomocysteinemia. Hyperhomocysteinemia may contribute to cardiovascular disease, venous thromboembolic disease, dementia, neuropsychiatric symptoms, and poor seizure control. Some clinicians recommend administering riboflavin, pyridoxine, and cyanocobalamin supplements in patients taking primidone (Apeland 2003; Apeland 2008; Belcastro 2010; Bochyńska 2012).
Primidone and its metabolites (PEMA, phenobarbital, and p-hydroxyphenobarbital) cross the placenta; neonatal serum concentrations at birth are similar to those in the mother. Withdrawal symptoms may occur in the neonate and may be delayed due to the long half-life of primidone and its metabolites. Use may be associated with birth defects and adverse events; the use of folic acid throughout pregnancy and vitamin K during the last month of pregnancy is recommended. Epilepsy itself, number of medications, genetic factors, or a combination of these probably influence the teratogenicity of antiseizure therapy.
Patients exposed to primidone during pregnancy are encouraged to enroll themselves into the NAAED Pregnancy Registry by calling 1-888-233-2334. Additional information is available at www.aedpregnancyregistry.org.
CNS status, seizure activity, liver enzymes, CBC with differential, renal function, serum concentrations; signs and symptoms of suicidality (eg, anxiety, depression, behavior changes)
Monitor both primidone and phenobarbital concentrations.
Primidone: Therapeutic: 5 to 12 mcg/mL (SI: 23 to 55 micromoles/L)
Phenobarbital: Note: Generally, not therapeutically useful in neonates on primidone therapy.
Therapeutic:
Infants, Children, and Adolescents: 15 to 40 mcg/mL (SI: 65 to 172 micromole/L)
Adults: 20 to 40 mcg/mL (SI: 86 to 172 micromole/L)
Toxic: >40 mcg/mL (SI: >172 micromole/L)
Toxic concentration: Slowness, ataxia, nystagmus: 35 to 80 mcg/mL (SI: 150 to 344 micromole/L)
Coma with reflexes: 65 to 117 mcg/mL (SI: 279 to 502 micromole/L)
Coma without reflexes: >100 mcg/mL (SI: >430 micromole/L)
Decreases neuron excitability, raises seizure threshold similar to phenobarbital; primidone has two active metabolites, phenobarbital and phenylethylmalonamide (PEMA); PEMA may enhance the activity of phenobarbital
Absorption: Well absorbed (Neels 2004)
Distribution: Vd: 0.6 to 0.75 L/kg (Bourgeois 2000; Neels 2004)
Protein binding: <20% (Bourgeois 2000; Neels 2004)
Metabolism: Hepatic to phenobarbital (active) by oxidation and to phenylethylmalonamide (PEMA; active) by ring cleavage at the second carbon position (El-Masri 1998)
Bioavailability: >90% (Bourgeois 2000)
Half-life elimination (age dependent): Primidone: 5 to16 hours (variable); PEMA: 16 to 50 hours (variable); Phenobarbital: 50 to 150 hours (Bourgeois 2000; Neels 2004)
Time to peak, serum: 0.5 to 9 hours (variable) (Neels 2004)
Excretion: Urine (15% to 65% as unchanged drug; the remainder is unconjugated PEMA, phenobarbital and its metabolites) (Neels 2004)
Tablets (Mysoline Oral)
50 mg (per each): $20.75
250 mg (per each): $71.40
Tablets (Primidone Oral)
50 mg (per each): $0.24 - $0.50
250 mg (per each): $0.45 - $1.00
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