Renal impairment is the major toxicity of foscarnet. Frequent monitoring of serum creatinine, with dose adjustment for changes in renal function, and adequate hydration with administration of foscarnet is imperative.
Seizures, related to alterations in plasma minerals and electrolytes, have been associated with foscarnet treatment. Therefore, patients must be carefully monitored for such changes and their potential sequelae. Mineral and electrolyte supplementation may be required.
Foscarnet is indicated for use only in immunocompromised patients with cytomegalovirus (CMV) retinitis and mucocutaneous acyclovir-resistant herpes simplex virus (HSV) infections.
Cytomegalovirus (CMV) infection, HIV-exposed/-infected: Limited data available (HHS [OI adult 2018]; HHS [OI pediatric 2016]):
Treatment; induction: In addition to antiviral therapy, antiretroviral therapy (ART) should be optimized.
CNS, neurological disease: Infants, Children, and Adolescents: IV: 180 mg/kg/day in divided doses every 8 or 12 hours; use in combination with ganciclovir; begin treatment promptly and continue until symptom improvement; follow with chronic suppression
GI disease (esophagitis or colitis); ganciclovir-intolerant or -resistant: Adolescents: IV: 180 mg/kg/day in divided doses every 8 or 12 hours for 21 to 42 days or until resolution of symptoms
Retinitis: Use as a component of initial therapy if immediate, sight-threatening lesions are present.
Infants and Children: IV: 180 mg/kg/day in divided doses every 8 or 12 hours; continue for 14 to 21 days. Use in combination with ganciclovir if monotherapy fails or in sight-threatening illnesses. Follow treatment with chronic suppression (HHS [OI pediatric 2016]).
Adolescents: Combination therapy with intravitreal and intravenous antiviral therapy recommended; follow treatment/induction with chronic suppression (HHS [OI adult 2018])
IV: 180 mg/kg/day in divided doses every 8 or 12 hours for 14 to 21 days
Intravitreal: 2.4 mg/dose for 1 to 4 doses administered over 7 to 10 days in combination with valganciclovir (oral), ganciclovir (IV), foscarnet (IV), or cidofovir (IV)
Chronic suppressive (maintenance) therapy:
Secondary prophylaxis (following treatment for prior disseminated disease, retinitis, or neurologic disease or GI disease with relapse): Infants, Children, and Adolescents: IV: 90 to 120 mg/kg/dose once daily; duration of therapy dependent on multiple factors (eg, infection, age, CD4 cell count, response) and is typically several months (HHS [OI adult 2018]; HHS [OI pediatric 2016])
Cytomegalovirus (CMV) infection after stem cell transplantation (HSCT); alternate agent: Limited data available (IDSA [Tomblyn 2009]): Infants, Children, and Adolescents: IV:
Preemptive therapy:
Induction:
<100 days post-transplant: Induction: 60 mg/kg/dose every 12 hours for 7 to 14 days; follow with maintenance therapy if CMV is still detectable and declining
>100 days post-transplant: 60 mg/kg/dose every 12 hours for 14 days; follow with maintenance therapy
Maintenance: 90 mg/kg/dose once daily; duration dependent on post-transplant days:
<100 days post-transplant: Minimum duration is at least 7 days and continue daily until CMV indicator test is negative
>100 days post-transplant: Continue for 7 to 14 days or until CMV indicator test is negative
Prophylactic therapy: Engraftment to <100 days post-transplant: 60 mg/kg/dose every 12 hours for 7 days, followed by 90 to 120 mg/kg/dose once daily until day 100 after HSCT
Herpes simplex virus (HSV) infection acyclovir-resistant; treatment, HIV-exposed/-infected: Limited data available:
Infants and Children: IV: 120 mg/kg/day in divided doses every 8 or 12 hours; duration depends on infection site (HHS [OI pediatric 2016])
Adolescents: IV: 80 to 120 mg/kg/day in divided doses every 8 or 12 hours; continue until clinical response (HHS [OI adult 2018])
Varicella zoster virus (VZ) infection, HIV-exposed/-infected: Limited data available:
Chickenpox not responding to acyclovir; treatment: Infants and Children: IV: 120 to 180 mg/kg/day in divided doses every 8 hours for 7 to 10 days or until no new lesions have appeared for 48 hours (HHS [OI pediatric 2016])
Zoster: Progressive outer retinal necrosis; treatment (HHS [OI adult 2018]; HHS [OI pediatric 2016]): Infants, Children, and Adolescents: Note: In addition to antiviral therapy, optimize ART.
IV: 90 mg/kg/dose every 12 hours in combination with ganciclovir (systemic, IV) and intravitreal foscarnet and/or ganciclovir
Intravitreal: 1.2 mg/0.05 mL per dose twice weekly in combination with systemic foscarnet and ganciclovir and/or intravitreal ganciclovir
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
There are no pediatric specific dosage adjustments available; based on experience in adult patients, dosage adjustment is suggested. Foscarnet is highly removed by hemodialysis (up to ~38% in 2.5 hours HD with high-flux membrane in adults) (Aweeka 1999)
There are no dosage adjustments provided in the manufacturer's labeling.
(For additional information see "Foscarnet: Drug information")
Cytomegalovirus, treatment:
Gastrointestinal disease (esophagitis, colitis) (alternative agent) (off-label use): IV: 60 mg/kg/dose every 8 hours or 90 mg/kg/dose every 12 hours for 21 to 42 days or until symptom resolution (HHS [OI adult 2020]).
Neurological disease (off-label use): IV: 60 mg/kg/dose every 8 hours or 90 mg/kg/dose every 12 hours in combination with ganciclovir; optimal duration not established (HHS [OI adult 2020]).
Ophthalmic disease (retinitis):
IV (alternative agent):
Induction treatment: 60 mg/kg/dose every 8 hours or 90 mg/kg/dose every 12 hours for 14 to 21 days; for immediate sight-threatening lesions, administer in combination with intravitreal therapy (HHS [OI adult 2020]).
Maintenance therapy: 90 to 120 mg/kg/dose once daily; due to lower toxicity, begin with 90 mg/kg/dose once daily, may escalate to 120 mg/kg/dose once daily if lower dose tolerated or for retinitis progression (manufacturer’s labeling). Duration of maintenance therapy is ≥3 to 6 months and until lesions are inactive and until CD4 count is >100 cells/mm3 for 3 to 6 months in response to antiretroviral therapy in patients with HIV (HHS [OI adult 2020]).
Intravitreal (off label):
Induction treatment: 2.4 mg per 0.1 mL injected into vitreum (Diaz-Llopis 1994; HHS [OI adult 2020]) for 1 to 4 doses administered over 7 to 10 days for immediate sight-threatening lesions; must be used in combination with systemic antiviral therapy (HHS [OI adult 2020]).
Cytomegalovirus prevention, allogeneic hematopoietic cell transplant recipients (off-label use; alternative agent):
Preemptive therapy: IV:
<100 days post-transplant: Induction: 60 mg/kg/dose every 12 hours for 7 to 14 days, followed by maintenance therapy: 90 mg/kg/dose once daily if CMV is still detectable and declining, continue until indicator test is negative. Minimum total duration (induction and maintenance) is 2 weeks (ASBMT/IDSA [Tomblyn 2009]).
>100 days post-transplant: 60 mg/kg/dose every 12 hours for 14 days, continue treatment with 90 mg/kg/dose once daily for 7 to 14 days or until indicator test is negative (ASBMT/IDSA [Tomblyn 2009]).
Prophylactic therapy: IV: 60 mg/kg/dose every 12 hours for 7 days, followed by 90 to 120 mg/kg/dose once daily until day 100 after HCT (ASBMT/IDSA [Tomblyn 2009]).
Herpes simplex infection, mucocutaneous (acyclovir-resistant):
IV: 40 mg/kg/dose every 8 to 12 hours for 14 to 21 days or until healed.
Topical (off label): Patients with HIV: Apply foscarnet 1% (extemporaneously prepared) 5 times daily for ≥21 to 28 days, based on clinical response (HHS [OI adult 2020]).
Varicella zoster virus, progressive outer retinal necrosis (off-label use):
Intravitreal (off-label): 1.2 mg per 0.05 mL injected in the vitreum twice weekly; must be used in combination with systemic antiviral therapy (HHS [OI adult 2020]).
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
See tables. Note: Renal function may be estimated by dividing actual 24-hour CrCl (mL/minute) by body weight (kg) or by using the modified Cockcroft-Gault formula ([140 − age]/[serum creatinine in mg/dL × 72] [× 0.85 for females]) for dosage adjustment purposes.
CrCl (mL/min/kg) |
HSV |
HSV |
CMV |
CMV |
---|---|---|---|---|
Equivalent to 40 mg/kg every 12 hours |
Equivalent to 40 mg/kg every 8 hours |
Equivalent to 60 mg/kg every 8 hours |
Equivalent to 90 mg/kg every 12 hours | |
<0.4 |
Not recommended |
Not recommended |
Not recommended |
Not recommended |
≥0.4-0.5 |
20 mg/kg every 24 hours |
35 mg/kg every 24 hours |
50 mg/kg every 24 hours |
50 mg/kg every 24 hours |
>0.5-0.6 |
25 mg/kg every 24 hours |
40 mg/kg every 24 hours |
60 mg/kg every 24 hours |
60 mg/kg every 24 hours |
>0.6-0.8 |
35 mg/kg every 24 hours |
25 mg/kg every 12 hours |
40 mg/kg every 12 hours |
80 mg/kg every 24 hours |
>0.8-1 |
20 mg/kg every 12 hours |
35 mg/kg every 12 hours |
50 mg/kg every 12 hours |
50 mg/kg every 12 hours |
>1-1.4 |
30 mg/kg every 12 hours |
30 mg/kg every 8 hours |
45 mg/kg every 8 hours |
70 mg/kg every 12 hours |
>1.4 |
40 mg/kg every 12 hours |
40 mg/kg every 8 hours |
60 mg/kg every 8 hours |
90 mg/kg every 12 hours |
CrCl (mL/min/kg) |
CMV |
CMV |
---|---|---|
Equivalent to 90 mg/kg every 24 hours |
Equivalent to 120 mg/kg every 24 hours | |
<0.4 |
Not recommended |
Not recommended |
≥0.4-0.5 |
50 mg/kg every 48 hours |
65 mg/kg every 48 hours |
>0.5-0.6 |
60 mg/kg every 48 hours |
80 mg/kg every 48 hours |
>0.6-0.8 |
80 mg/kg every 48 hours |
105 mg/kg every 48 hours |
>0.8-1 |
50 mg/kg every 24 hours |
65 mg/kg every 24 hours |
>1-1.4 |
70 mg/kg every 24 hours |
90 mg/kg every 24 hours |
>1.4 |
90 mg/kg every 24 hours |
120 mg/kg every 24 hours |
Hemodialysis:
Foscarnet is highly removed by hemodialysis (up to ~38% in 2.5 hours HD with high-flux membrane) (Aweeka 1999)
Doses of 45 to 60 mg/kg/dose posthemodialysis (3 times/week) with the monitoring of weekly plasma concentrations to maintain peak plasma concentrations in the range of 500 to 800 micromolar for the treatment of CMV infection have been recommended (Aweeka 1999; Jayasekara 1999; MacGregor 1991)
Peritoneal dialysis: HSV infection (localized or disseminated): IV: 60 mg/kg/dose every 48 to 72 hours; higher doses may be necessary for herpes encephalitis or herpes zoster infection (Jayasekara 1999)
There are no dosage adjustments provided in manufacturer’s labeling.
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Solution, Intravenous [preservative free]:
Foscavir: 24 mg/mL (250 mL)
Generic: 24 mg/mL (250 mL)
Yes
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Solution, Intravenous:
Vocarvi: 24 mg/mL (250 mL)
Parenteral:
IV: Administer using an infusion pump at a rate not to exceed 1 mg/kg/minute (ie, 60 mg/kg/dose over 1 hour or 120 mg/kg/dose over 2 hours) (HHS [OI pediatric 2016]).
Hydration:
Initial: Prehydration prior to initial infusion: Children: 10 to 20 mL/kg (maximum: 1,000 mL) of age-appropriate fluid (usually NS); adults: 750 to 1,000 mL NS or D5W
Subsequent foscarnet doses: Concurrent hydration: Children: 10 to 20 mL/kg (maximum: 1,000 mL) of age-appropriate fluid; adults: 500 to 1,000 mL NS or D5W; concurrent hydration volume is dependent on foscarnet dose
Intravitreal: Administer undiluted (24 mg/mL) in appropriate sterile setting by health care professional experienced in administration of intravitreal ophthalmic injections.
IV: Foscarnet is administered by intravenous infusion, using an infusion pump, at a rate not exceeding 1 mg/kg/minute. Adult induction doses of 60 mg/kg are administered over 1 hour. Adult maintenance doses of 90 to 120 mg/kg are infused over 2 hours. Undiluted (24 mg/mL) solution can be administered without further dilution when using a central venous catheter for infusion. For peripheral vein administration, the solution must be diluted to a final concentration of 12 mg/mL. The manufacturer recommends 750 to 1,000 mL of NS or D5W be administered prior to first infusion to establish diuresis. With subsequent infusions of 90 to 120 mg/kg, this volume would be repeated. If the dose were 40 to 60 mg/kg, then the volume could be reduced to 500 mL. After the first dose, the hydration fluid should be administered concurrently with foscarnet.
Intravitreal: Off-label route: Withdraw solution directly from infusion container as it is already diluted to appropriate concentration for intravitreal administration. Pass through 0.22 micron filter prior to injection (Diaz-Llopis 1994; Martinez-Castillo 2012).
Store intact container at room temperature of 20°C to 25°C (68°F to 77°F) and protect from temperatures >40°C (>104°F) and from freezing. Following dilution in D5W or NS, solutions are stable for 24 hours at room temperature or under refrigeration.
Treatment of CMV retinitis in patients with acquired immunodeficiency syndrome (AIDS) (FDA approved in adults); treatment of acyclovir-resistant mucocutaneous herpes simplex virus infections in immunocompromised patients and acyclovir-resistant herpes zoster infections (FDA approved in adults)
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.
>10%:
Central nervous system: Headache (26%)
Endocrine & metabolic: Hypokalemia (16% to 48%), hypocalcemia (15% to 30%), hypomagnesemia (15% to 30%), hypophosphatemia (8% to 26%)
Gastrointestinal: Nausea (47%), diarrhea (30%), vomiting (26%)
Hematologic & oncologic: Anemia (33%), granulocytopenia (17%)
Renal: Renal insufficiency (27%)
Miscellaneous: Fever (65%)
1% to 10%:
Cardiovascular: Chest pain (1% to 5%; including transient chest pain as part of infusion reactions), edema (1% to 5%), facial edema (1% to 5%), first degree atrioventricular block (1% to 5%), flushing (1% to 5%), hypertension (1% to 5%), hypotension (1% to 5%), palpitations (1% to 5%), sinus tachycardia (1% to 5%), ST segment changes on ECG (1% to 5%), thrombosis (1% to 5%)
Central nervous system: Seizure (10%), anxiety (≥5%), confusion (≥5%), depression (≥5%), dizziness (≥5%), fatigue (≥5%), hypoesthesia (≥5%), malaise (≥5%), neuropathy (≥5%), pain (≥5%), paresthesia (≥5%), rigors (≥5%), abnormal electroencephalogram (1% to 5%), aggressive behavior (1% to 5%), agitation (1% to 5%), amnesia (1% to 5%), aphasia (1% to 5%), ataxia (1% to 5%), cerebrovascular disease (1% to 5%), dementia (1% to 5%), hallucination (1% to 5%), insomnia (1% to 5%), meningitis (1% to 5%), nervousness (1% to 5%), sensory disturbance (1% to 5%), somnolence (1% to 5%), stupor (1% to 5%)
Dermatologic: Diaphoresis (≥5%), skin rash (≥5%), dermal ulcer (1% to 5%), erythematous rash (1% to 5%), maculopapular rash (1% to 5%), pruritus (1% to 5%), seborrhea (1% to 5%), skin discoloration (1% to 5%)
Endocrine & metabolic: Hyperphosphatemia (6%), electrolyte disturbance (≥5%), abnormal albumin-Globulin ratio (1% to 5%), acidosis (1% to 5%), albuminuria (1% to 5%), cachexia (1% to 5%), hyponatremia (1% to 5%), increased lactate dehydrogenase (1% to 5%), increased thirst (1% to 5%), weight loss (1% to 5%)
Gastrointestinal: Abdominal pain (≥5%), anorexia (≥5%), aphthous stomatitis (1% to 5%), cachexia (1% to 5%), constipation (1% to 5%), dysgeusia (1% to 5%), dyspepsia (1% to 5%), dysphagia (1% to 5%), flatulence (1% to 5%), melena (1% to 5%), pancreatitis (1% to 5%), xerostomia (1% to 5%)
Genitourinary: Nephrotoxicity (8%), dysuria (1% to 5%), nocturia (1% to 5%), urinary retention (1% to 5%), urinary tract infection (1% to 5%)
Hematologic & oncologic: Bone marrow suppression (10%), leukopenia (≥5%), mineral abnormalities (≥5%), neutropenia (≥5%), abnormal white cell differential (1% to 5%), altered platelet function (1% to 5%), lymphadenopathy (1% to 5%), pseudolymphoma (1% to 5%), rectal hemorrhage (1% to 5%), sarcoma (1% to 5%), thrombocytopenia (1% to 5%)
Hepatic: Abnormal hepatic function tests (1% to 5%), increased lactate dehydrogenase (1% to 5%), increased serum alkaline phosphatase (1% to 5%), increased serum ALT (1% to 5%), increased serum AST (1% to 5%)
Infection: Infection (≥5%), sepsis (≥5%), abscess, bacterial infection (1% to 5%), fungal infection (1% to 5%)
Local: Inflammation at injection site (1% to 5%), pain at injection site (1% to 5%)
Neuromuscular & skeletal: Muscle spasm (≥5%), neuropathy (peripheral; ≥5%), weakness (≥5%), arthralgia (1% to 5%), back pain (1% to 5%), leg cramps (1% to 5%), myalgia (1% to 5%), tremor (1% to 5%)
Ophthalmic: Visual disturbance (≥5%), conjunctivitis (1% to 5%), eye pain (1% to 5%)
Renal: Decreased creatinine clearance (≥5%), increased serum creatinine (≥5%), acute renal failure (1% to 5%), increased blood urea nitrogen (1% to 5%), polyuria (1% to 5%)
Respiratory: Cough (≥5%), dyspnea (≥5%), bronchospasm (1% to 5%), flu-like symptoms (1% to 5%), hemoptysis (1% to 5%), pharyngitis (1% to 5%), pneumonia (1% to 5%), pneumothorax (1% to 5%), pulmonary infiltrates (1% to 5%), respiratory failure (1% to 5%), respiratory insufficiency (1% to 5%), rhinitis (1% to 5%), sinusitis (1% to 5%), stridor (1% to 5%)
<1%, postmarketing, and/or case reports: Coma, dehydration, diabetes insipidus (usually nephrogenic), erythema multiforme, esophageal ulcer, extravasation, Fanconi syndrome, gastrointestinal hemorrhage, glomerulonephritis, hematuria, hypercalcemia, hypersensitivity reaction (including anaphylactic shock, angioedema, urticaria), hypoproteinemia, increased amylase, increased creatine phosphokinase, increased gamma-glutamyl transferase, increased serum lipase, local irritation (genitals), localized edema, myasthenia, myopathy, myositis, nephrolithiasis, nephrotic syndrome, pancytopenia, penile ulceration, prolonged QT interval on ECG, proteinuria, renal disease (crystal-induced), renal tubular acidosis, renal tubular necrosis, rhabdomyolysis, SIADH, status epilepticus, Stevens-Johnson syndrome, torsades de pointes, toxic epidermal necrolysis, vaginal ulcer, ventricular arrhythmia
Clinically significant hypersensitivity to foscarnet or any component of the formulation.
Concerns related to adverse effects:
• Dental effects: Foscarnet is deposited in teeth and bone of young, growing animals; it has adversely affected tooth enamel development in rats.
• Electrolyte imbalance: Imbalance of serum electrolytes or minerals occurs in at least 15% of patients (hypocalcemia, low ionized calcium, hyper/hypophosphatemia, hypomagnesemia, or hypokalemia); reducing infusion rate may decrease/prevent symptoms. Patients with low ionized calcium may experience perioral tingling, numbness, paresthesias, tetany, and seizures. Correct electrolytes before initiating therapy; use caution in patients who have any underlying electrolyte imbalances, those with neurologic or cardiac abnormalities, and those receiving medications that are influenced by calcium levels. Use caution when administering other medications that cause electrolyte imbalances. Patients who experience signs or symptoms of an electrolyte imbalance should be assessed immediately.
• Hematologic effects: May cause anemia and granulocytopenia.
• Hypersensitivity: Serious hypersensitivity reactions, including anaphylactic shock and angioedema, have been reported. Discontinue immediately and institute appropriate medical therapy if an acute reaction occurs.
• Renal impairment: [US Boxed Warning]: Renal impairment occurs to some degree in the majority of patients treated with foscarnet; renal impairment may occur at any time (though typically during second week of induction therapy) and is usually reversible within 1 week following dose adjustment or discontinuation of therapy, however, several patients have died with renal failure within 4 weeks of stopping foscarnet; therefore, renal function should be closely monitored during both induction and maintenance therapy. To reduce the risk of nephrotoxicity and the potential to administer a relative overdose, always calculate the CrCl even if serum creatinine is within the normal range. Dosage adjustments are recommended for renal dysfunction; safety and efficacy in patients with a baseline Scr >2.8 mg/dL or CrCl <50 mL/minute are limited. Use in patients with CrCl <0.4 mL/kg/minute is not recommended. Adequate hydration may reduce the risk of nephrotoxicity; the manufacturer makes specific recommendations regarding this (see Administration).
• QT prolongation: QT prolongation, including torsades de pointes, has been reported; some reports occurred in patients with confounding risk factors (eg, underlying cardiac disease, electrolyte abnormalities, concomitant medications). Use with caution in patients with a history of QT prolongation or those at increased risk for QT prolongation.
• Seizures: [US Boxed Warning]: Seizures related to plasma electrolyte/mineral imbalance may occur; incidence has been reported in up to 10% of HIV patients. Risk factors for seizures include impaired baseline renal function, low total serum calcium, and underlying CNS condition. Some patients who have experienced seizures have been able to continue or resume foscarnet treatment after their mineral or electrolyte abnormality has been corrected, their underlying disease state treated, or their dose decreased.
• Vascular irritant: Administer only into vein with adequate blood flow to prevent tissue irritation/ulceration. Genital vascular tissue damage has been reported; adequate hydration recommended.
Disease related concerns:
• Heart failure: Due to sodium content, use with caution in patients with heart failure.
Other warnings/precautions:
• Appropriate use: [US Boxed Warning]: Indicated only for immunocompromised patients with CMV retinitis and mucocutaneous acyclovir-resistant HSV infection.
None known.
Acyclovir-Valacyclovir: Foscarnet may enhance the nephrotoxic effect of Acyclovir-Valacyclovir. Risk X: Avoid combination
Aminoglycosides: Foscarnet may enhance the nephrotoxic effect of Aminoglycosides. Risk X: Avoid combination
Amphotericin B: Foscarnet may enhance the nephrotoxic effect of Amphotericin B. Risk X: Avoid combination
CycloSPORINE (Systemic): Foscarnet may enhance the nephrotoxic effect of CycloSPORINE (Systemic). Risk X: Avoid combination
Haloperidol: QT-prolonging Agents (Indeterminate Risk - Caution) may enhance the QTc-prolonging effect of Haloperidol. Risk C: Monitor therapy
Loop Diuretics: May increase the serum concentration of Foscarnet. Management: When diuretics are indicated during foscarnet treatment, thiazides are recommended over loop diuretics. If patients receive loop diuretics during foscarnet treatment, monitor closely for evidence of foscarnet toxicity. Risk D: Consider therapy modification
Methotrexate: Foscarnet may enhance the nephrotoxic effect of Methotrexate. Risk X: Avoid combination
Pentamidine (Systemic): May enhance the adverse/toxic effect of Foscarnet. The specific toxicities may include hypocalcemia, renal failure, and QT-prolongation. Management: Consider alternatives to this combination when possible. If this combination must be used, monitor patients more closely for hypocalcemia, renal dysfunction, and QT interval prolongation. Risk D: Consider therapy modification
QT-prolonging Agents (Highest Risk): QT-prolonging Agents (Indeterminate Risk - Caution) may enhance the QTc-prolonging effect of QT-prolonging Agents (Highest Risk). Management: Monitor for QTc interval prolongation and ventricular arrhythmias when these agents are combined. Patients with additional risk factors for QTc prolongation may be at even higher risk. Risk C: Monitor therapy
Tacrolimus (Systemic): Foscarnet may enhance the nephrotoxic effect of Tacrolimus (Systemic). Risk X: Avoid combination
Talimogene Laherparepvec: Antiherpetic Antivirals may diminish the therapeutic effect of Talimogene Laherparepvec. Risk C: Monitor therapy
Vasopressin: Drugs Suspected of Causing Diabetes Insipidus may diminish the therapeutic effect of Vasopressin. Specifically, the pressor and antidiuretic hormone effects of vasopressin may be decreased. Risk C: Monitor therapy
Some products may contain sodium.
Information related to use of foscarnet in pregnancy is limited (Alvarez-McLeod 1999).
Foscarnet is not the preferred treatment of cytomegalovirus infection in pregnant patients. Monitoring of amniotic fluid volumes by ultrasound is recommended weekly after 20 weeks of gestation to detect oligohydramnios if foscarnet is used. In general, intravitreous injections for local therapy are preferred for retinal disease to limit systemic exposure (HHS [OI adult 2020]).
24-hour creatinine clearance, ECG, and electrolytes at baseline and periodically thereafter (when clinically appropriate). During induction therapy: Obtain complete blood counts and electrolytes (including serum creatinine, calcium, magnesium, potassium, and phosphorus) twice weekly and then once weekly during maintenance therapy. More frequent monitoring may be required in some patients. Check hydration status before and after infusion.
Pyrophosphate analogue which acts as a noncompetitive inhibitor of many viral RNA and DNA polymerases as well as HIV reverse transcriptase. Similar to ganciclovir, foscarnet is a virostatic agent. Foscarnet does not require activation by thymidine kinase.
Distribution: Vd: ~0.5 L/kg; up to 28% of cumulative IV dose may be deposited in bone
Protein binding: 14% to 17%
Metabolism: Biotransformation does not occur
Half-life elimination: Elimination: ~3 to 4 hours; terminal: ~88 hours (due to bone deposition)
Excretion: Urine (≤28% as unchanged drug)
Renal function impairment: CrCl of 50 to 80 mL/minute has a clearance of about 1.33 mL/minute/kg and a plasma half-life of about 3.35 hours. CrCl of 25 to 49 mL/minute has a clearance of about 0.46 mL/minute/kg and a plasma half-life of about 13 hours. CrCl of 10 to 24 mL/minute has a clearance of 0.43 mL/minute/kg and plasma half-life about 25.3 hours.
Solution (Foscarnet Sodium Intravenous)
6000 mg/250 mL (per mL): $2.27
Solution (Foscavir Intravenous)
6000 mg/250 mL (per mL): $2.30
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