Muscle spasm:
Note: For skeletal muscle spasm and/or pain (eg, low back pain, neck pain) with muscle spasm, usually in combination with a nonsteroidal anti-inflammatory drug and/or acetaminophen (ACP [Chou 2017]; van Tulder 2003). In general, muscle relaxants should be used temporarily (eg, for a few days or intermittently for a few days when needed) (APS 2016).
Oral: 1.5 g 3 to 4 times daily for 2 to 3 days (up to 8 g/day may be given in severe conditions), then decrease dose to ≤4.5 g/day in 3 to 4 divided doses (eg, 1.5 g 3 times daily or 750 mg 4 times daily) (Emrich 2015; Friedman 2018; manufacturer's labeling).
IM, IV: Initial: 1 g; may repeat every 8 hours; maximum dose: 3 g/day for no more than 3 consecutive days. If condition persists, may repeat course of therapy after a drug-free interval of 48 hours.
The renal dosing recommendations are based upon the best available evidence and clinical expertise. Senior Editorial Team: Bruce Mueller, PharmD, FCCP, FASN, FNKF; Jason Roberts, PhD, BPharm (Hons), B App Sc, FSHP, FISAC; Michael Heung, MD, MS.
IV: Use contraindicated in patients with kidney impairment due to the presence of polyethylene glycol (manufacturer's labeling).
Oral:
Altered kidney function: Mild to severe impairment: Limited data suggest no dosage adjustment necessary (Sica 1990; expert opinion); use with caution (expert opinion).
Hemodialysis, intermittent (thrice weekly): Unknown dialyzability: No dosage adjustment necessary (Sica 1990); drowsiness has been described in patients with end-stage kidney disease (ESKD) (Sica 1990); use with caution (expert opinion).
Peritoneal dialysis: Unknown dialyzability: No dosage adjustment necessary (expert opinion); drowsiness has been described in patients with ESKD (Sica 1990); use with caution (expert opinion).
No dosage adjustment provided in manufacturer’s labeling. However, elimination may be reduced in patients with cirrhosis.
(For additional information see "Methocarbamol: Pediatric drug information")
Muscle spasm: Adolescents ≥16 years: Oral: 1,500 mg 4 times daily for 2 to 3 days; maximum daily dose: 8 g/day (reserved for severe conditions); then decrease dose to 4,000 to 4,500 mg/day in 3 to 6 divided doses (ie, 1,000 mg 4 times daily or 750 mg every 4 hours or 1,500 mg 3 times/day)
Tetanus: Note: Use has generally been replaced by other agents (eg, benzodiazepines) (Hsu 2001): Infants, Children, and Adolescents: IV: 15 mg/kg/dose or 500 mg/m2/dose, may repeat every 6 hours as needed; usual adult dose: 1,000 to 2,000 mg/dose; maximum total dose: 1.8 g/m2 for 3 days; in adults, injection is not recommended for use longer than 3 days
Children and Adolescents: There are no dosage adjustments provided in the manufacturer's labeling; however, administration of the parenteral formulation is contraindicated in patients with renal dysfunction due to the presence of polyethylene glycol.
There are no dosage adjustments provided in the manufacturer's labeling; however, elimination may be reduced in patients with cirrhosis.
Avoid use (Beers Criteria [AGS 2019]).
Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product
Solution, Injection:
Robaxin: 1000 mg/10 mL (10 mL) [pyrogen free; contains polyethylene glycol 300]
Generic: 1000 mg/10 mL (10 mL)
Solution, Injection [preservative free]:
Robaxin: 1000 mg/10 mL (10 mL) [contains polyethylene glycol 300]
Generic: 1000 mg/10 mL (10 mL)
Tablet, Oral:
Robaxin: 500 mg [DSC] [scored; contains fd&c yellow #6 (sunset yellow), saccharin sodium]
Robaxin-750: 750 mg [DSC] [contains fd&c yellow #10 (quinoline yellow), fd&c yellow #6 (sunset yellow), saccharin sodium]
Generic: 500 mg, 750 mg
Yes
Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product
Solution, Injection:
Robaximol: 100 mg/mL ([DSC])
Generic: 100 mg/mL (10 mL)
Solution for injection:
IM: A maximum of 5 mL can be administered into each gluteal region.
IV: Maximum rate: 3 mL/minute; may be administered undiluted or diluted. Monitor closely for extravasation. Administer IV while in recumbent position. Maintain position for at least 10-15 minutes following infusion.
Tablet: May be crushed and mixed with food or liquid if needed.
Oral: Tablet: May be crushed and mixed with food or liquid if needed.
Parenteral:
IV: May be directly injected undiluted at a maximum rate of 3 mL/minute; may also be further diluted and infused more slowly; patient should be in the recumbent position during and for 10 to 15 minutes after IV administration. Monitor closely for extravasation.
IM: Adults: Maximum of 5 mL can be administered into each gluteal region; not recommended for SubQ administration
Muscle spasm: Adjunctive treatment of muscle spasm associated with acute painful musculoskeletal conditions.
Methocarbamol may be confused with mephobarbital
Robaxin may be confused with ribavirin, Skelaxin
Beers Criteria: Methocarbamol is identified in the Beers Criteria as a potentially inappropriate medication to be avoided in patients 65 years and older (independent of diagnosis or condition) because most muscle relaxants are poorly tolerated in older adults due to anticholinergic effects caused by some muscle relaxants, risk of sedation, and an increased risk of fracture. In addition, efficacy is questionable at doses tolerated by geriatric patients (Beers Criteria [AGS 2019]).
Pharmacy Quality Alliance (PQA): Methocarbamol (as a single agent or as part of a combination product) is identified as a high-risk medication in patients 65 years and older on the PQA’s Use of High-Risk Medications in the Elderly (HRM) performance measure, a safety measure used by the Centers for Medicare and Medicaid Services (CMS) for Medicare plans (PQA 2017).
Robaxin [US, Canada, Great Britain, Greece, Spain] may be confused with Rubex brand name for ascorbic acid [Ireland]; doxorubicin [Brazil]
Methocarbamol may cause CNS effects, including (but not limited to) dizziness and drowsiness, which may impair physical or mental abilities (Ref). Confusion and sedated state may also occur (Ref). Methocarbamol has been associated with an increased risk of accidental injury (including falling and bone fracture) in older adults (Ref).
Mechanism: Related to the pharmacologic action (ie, global CNS depression) (Ref).
Risk factors:
• Continuous use within the prior 60 days (increased risk of injuries in older adults) (Ref)
• Concurrent use of alcohol or other CNS depressants
• Older adults (>65 years) (Ref)
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.
Frequency not defined:
Cardiovascular: Bradycardia, flushing, hypotension, syncope, thrombophlebitis
Dermatologic: Pruritus, skin rash, urticaria
Gastrointestinal: Dyspepsia, nausea, vomiting
Hematologic & oncologic: Leukopenia
Hepatic: Cholestatic jaundice, jaundice
Hypersensitivity: Anaphylaxis, angioedema
Local: Local skin exfoliation (injection), pain at injection site
Nervous system: Amnesia, ataxia, confusion, headache, insomnia, metallic taste, sedated state, seizure, vertigo
Ophthalmic: Blurred vision, conjunctivitis, diplopia, nystagmus disorder
Respiratory: Nasal congestion
Miscellaneous: Fever
Postmarketing:
Nervous system: Dizziness (Friedman 2018), drowsiness (Friedman 2018), falling (Spence 2013)
Neuromuscular & skeletal: Bone fracture (Spence 2013)
Miscellaneous: Accidental injury (Spence 2013)
Hypersensitivity to methocarbamol or any component of the formulation; renal impairment (injection formulation)
Disease-related concerns:
• Hepatic impairment: Plasma protein binding and clearance are decreased and the half-life is increased in patients with hepatic impairment.
• Renal impairment: Use of IV formulation is contraindicated.
• Seizure disorder: Use the oral formulation with caution in patients with a history of seizure disorder. Intravenous administration to patients with a seizure disorder is not recommended.
Special populations:
• Pediatric: IV formulation: Recommended only for the treatment of tetanus in pediatric patients.
Dosage form specific issues:
• Injection: Contraindicated in renal impairment. Contains polyethylene glycol. Rate of injection should not exceed 3 mL/minute; solution is hypertonic; avoid extravasation.
None known.
Alcohol (Ethyl): CNS Depressants may enhance the CNS depressant effect of Alcohol (Ethyl). Risk C: Monitor therapy
Alizapride: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Azelastine (Nasal): May enhance the CNS depressant effect of CNS Depressants. Risk X: Avoid combination
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
Botulinum Toxin-Containing Products: Muscle Relaxants (Centrally Acting) may enhance the adverse/toxic effect of Botulinum Toxin-Containing Products. Specifically, the risk for increased muscle weakness may be enhanced. Risk C: Monitor therapy
Brexanolone: CNS Depressants may enhance the CNS depressant effect of Brexanolone. Risk C: Monitor therapy
Brimonidine (Topical): May enhance the CNS depressant effect of CNS Depressants. 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: CNS Depressants may enhance the CNS depressant effect of Buprenorphine. Management: Consider reduced doses of other CNS depressants, and avoiding such drugs in patients at high risk of buprenorphine overuse/self-injection. Initiate buprenorphine at lower doses in patients already receiving CNS depressants. Risk D: Consider therapy modification
Cannabinoid-Containing Products: CNS Depressants may enhance the CNS depressant effect of Cannabinoid-Containing Products. 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
CNS Depressants: May enhance the adverse/toxic effect of other CNS Depressants. Risk C: Monitor therapy
Daridorexant: May enhance the CNS depressant effect of CNS Depressants. Management: Dose reduction of daridorexant and/or any other CNS depressant may be necessary. Use of daridorexant with alcohol is not recommended, and the use of daridorexant with any other drug to treat insomnia is not recommended. Risk D: Consider therapy modification
Difelikefalin: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Dimethindene (Topical): May enhance the CNS depressant effect of CNS Depressants. 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
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
Eperisone: May enhance the adverse/toxic effect of Methocarbamol. Risk C: Monitor therapy
Esketamine: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
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
HydrOXYzine: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Kava Kava: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Kratom: May enhance the CNS depressant effect of CNS Depressants. Risk X: Avoid combination
Lemborexant: May enhance the CNS depressant effect of CNS Depressants. Management: Dosage adjustments of lemborexant and of concomitant CNS depressants may be necessary when administered together because of potentially additive CNS depressant effects. Close monitoring for CNS depressant effects is necessary. 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
Magnesium Sulfate: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
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
Metoclopramide: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
MetyroSINE: CNS Depressants may enhance the sedative effect of MetyroSINE. Risk C: Monitor therapy
Minocycline (Systemic): May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Olopatadine (Nasal): May enhance the CNS depressant effect of CNS Depressants. Risk X: Avoid combination
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
Orphenadrine: CNS Depressants may enhance the CNS depressant effect of Orphenadrine. Risk X: Avoid combination
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: CNS Depressants may enhance the CNS depressant effect of OxyCODONE. Management: Avoid concomitant use of oxycodone 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
Paraldehyde: CNS Depressants may enhance the CNS depressant effect of Paraldehyde. Risk X: Avoid combination
Perampanel: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Piribedil: CNS Depressants may enhance the CNS depressant effect of Piribedil. Risk C: Monitor therapy
Pramipexole: CNS Depressants may enhance the sedative effect of Pramipexole. Risk C: Monitor therapy
Pyridostigmine: Methocarbamol may diminish the therapeutic effect of Pyridostigmine. Risk C: Monitor therapy
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 enhance the adverse/toxic effect of CNS Depressants. Specifically, sleepiness and dizziness may be enhanced. Risk C: Monitor therapy
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
Thalidomide: CNS Depressants may enhance the CNS depressant effect of Thalidomide. Risk X: Avoid combination
Tolperisone: May enhance the adverse/toxic effect of Muscle Relaxants (Centrally Acting). Management: Monitor for increased sedation or CNS effects if tolperisone is combined with other centrally acting muscle relaxants. Consider decreasing the tolperisone dose if these agents are combined. Risk D: Consider therapy modification
Trimeprazine: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Valerian: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
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
Animal reproduction studies have not been conducted. The manufacturer notes that fetal and congenital abnormalities have been reported following in utero exposure (Hall 1982).
It is not known if methocarbamol is present in breast milk. The manufacturer recommends that caution be exercised when administering methocarbamol to breastfeeding women.
Monitor closely for extravasation, bradycardia, hypotension (IV administration); mental alertness.
Causes skeletal muscle relaxation by general CNS depression
Onset of action: Muscle relaxation: Oral: ~30 minutes
Protein binding: 46% to 50%
Metabolism: Hepatic via dealkylation and hydroxylation
Half-life elimination: 1 to 2 hours
Time to peak, serum: Oral: 1 to 2 hours
Excretion: Urine (primarily as metabolites)
Clearance: Adults: 0.2 to 0.8 L/hour/kg
Renal function impairment: Clearance is decreased ~40% in patients with severe renal impairment.
Hepatic function impairment: Clearance is decreased ~70%; t1/2 is prolonged ~3-fold in cirrhosis patients.
Solution (Methocarbamol Injection)
1000 mg/10 mL (per mL): $0.75 - $7.13
Solution (Robaxin Injection)
1000 mg/10 mL (per mL): $0.96
Tablets (Methocarbamol Oral)
500 mg (per each): $0.13 - $15.73
750 mg (per each): $0.17 - $0.73
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