Version July 2025
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, nonretinitis tissue-invasive disease (eg, colitis, esophagitis, pneumonitis, neurological disease), treatment (alternative agent; off-label use):
IV: 60 mg/kg/dose every 8 hours or 90 mg/kg/dose every 12 hours for at least 2 to 3 weeks and often longer depending on site and severity of infection, type of immunocompromise, and clinical and virologic response days (Ref). For neurological disease, consider use in combination with ganciclovir (Ref).
Cytomegalovirus retinitis, treatment:
Induction therapy: Note: For immediate sight-threatening lesions (adjacent to optic nerve or fossa), use intravitreal therapy in combination with systemic therapy (Ref).
Intravitreal (off-label route): 2.4 mg per 0.1 mL administered as an intravitreal injection (Ref) once weekly until lesion inactivity is achieved; administer in combination with a systemic antiviral (Ref).
IV (alternative systemic agent): 60 mg/kg/dose every 8 hours or 90 mg/kg/dose every 12 hours for 14 to 21 days followed by maintenance therapy (Ref).
Chronic maintenance therapy (secondary prophylaxis) (alternative agent): IV: 90 to 120 mg/kg/dose once daily (Ref); 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 (Ref). For patients with HIV, continue for ≥3 to 6 months until CD4 count steadily >100 cells/mm3 on antiretroviral therapy and all lesions are inactive; for transplant recipients, duration varies depending on response and immunosuppression. Discontinue only after consultation with an ophthalmologist (Ref).
Cytomegalovirus, transplant (hematopoietic cell) recipients, preemptive therapy (alternative agent; off-label use):
IV: 60 mg/kg/dose every 8 hours or 90 mg/kg/dose every 12 hours for 2 weeks and until undetectable. May switch to maintenance therapy of 90 mg/kg/dose once daily after at least 1 to 2 weeks of induction therapy and substantial viral load reduction, then continue until undetectable (Ref).
Herpes simplex infection, mucocutaneous (acyclovir-resistant):
IV: 40 mg/kg/dose every 8 to 12 hours for 14 to 21 days or until healed.
Varicella zoster virus, progressive outer retinal necrosis (off-label use):
Intravitreal (off-label route): 1.2 mg per 0.05 mL administered as an intravitreal injection twice weekly in combination with systemic antiviral therapy (Ref).
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
The renal dosing recommendations are based upon the best available evidence and clinical expertise. Senior Editorial Team: Bruce Mueller, PharmD, FCCP, FASN, FNKF; Jason A. Roberts, PhD, BPharm (Hons), B App Sc, FSHP, FISAC; Michael Heung, MD, MS.
Altered kidney function:
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 |
Induction dosing |
Chronic maintenance therapy (secondary prophylaxis) | ||
|---|---|---|---|---|
|
Equivalent to 60 mg/kg IV every 8 hours |
Equivalent to 90 mg/kg IV every 12 hours |
Equivalent to 90 mg/kg every 24 hours |
Equivalent to 120 mg/kg every 24 hours | |
|
>1.4 mL/minute/kg |
60 mg/kg IV every 8 hours |
90 mg/kg IV every 12 hours |
90 mg/kg IV every 24 hours |
120 mg/kg IV every 24 hours |
|
>1 to 1.4 mL/minute/kg |
45 mg/kg IV every 8 hours |
70 mg/kg IV every 12 hours |
70 mg/kg IV every 24 hours |
90 mg/kg IV every 24 hours |
|
>0.8 to 1 mL/minute/kg |
50 mg/kg IV every 12 hours |
50 mg/kg IV every 12 hours |
50 mg/kg IV every 24 hours |
65 mg/kg IV every 24 hours |
|
>0.6 to 0.8 mL/minute/kg |
40 mg/kg IV every 12 hours |
80 mg/kg IV every 24 hours |
80 mg/kg IV every 48 hours |
105 mg/kg IV every 48 hours |
|
>0.5 to 0.6 mL/minute/kg |
60 mg/kg IV every 24 hours |
60 mg/kg IV every 24 hours |
60 mg/kg IV every 48 hours |
80 mg/kg IV every 48 hours |
|
≥0.4 to 0.5 mL/minute/kg |
50 mg/kg IV every 24 hours |
50 mg/kg IV every 24 hours |
50 mg/kg IV every 48 hours |
65 mg/kg IV every 48 hours |
|
<0.4 mL/minute/kg |
Not recommended |
Not recommended |
Not recommended |
Not recommended |
|
CrCl |
Equivalent to 40 mg/kg every 12 hours |
Equivalent to 40 mg/kg every 8 hours |
|---|---|---|
|
>1.4 mL/minute/kg |
40 mg/kg IV every 12 hours |
40 mg/kg IV every 8 hours |
|
>1 to 1.4 mL/minute/kg |
30 mg/kg IV every 12 hours |
30 mg/kg IV every 8 hours |
|
>0.8 to 1 mL/minute/kg |
20 mg/kg IV every 12 hours |
35 mg/kg IV every 12 hours |
|
>0.6 to 0.8 mL/minute/kg |
35 mg/kg IV every 24 hours |
25 mg/kg IV every 12 hours |
|
>0.5 to 0.6 mL/minute/kg |
25 mg/kg IV every 24 hours |
40 mg/kg IV every 24 hours |
|
≥0.4 to 0.5 mL/minute/kg |
20 mg/kg IV every 24 hours |
35 mg/kg IV every 24 hours |
|
<0.4 mL/minute/kg |
Not recommended |
Not recommended |
Augmented renal clearance (measured urinary CrCl ≥130 mL/minute/1.73 m2):
Note: Augmented renal clearance (ARC) is a phenomenon that occurs in certain critically ill patients and is characterized by increased SCr clearance and elimination of renally cleared medications, which could increase risk of therapeutic failure. Younger patients (<55 years of age) admitted post trauma or major surgery are at highest risk for ARC as are those with sepsis, burns, or hematologic malignancies. An 8- to 24-hour measured urinary CrCl is necessary to identify these patients (Ref).
Intravitreal: No data available. No dosage adjustment necessary as systemic absorption is likely to be limited (Ref).
IV: No data available. Theoretically, patients with ARC may need higher doses of foscarnet, although evidence to recommend a specific dose increase is lacking. Follow standard indication-specific dosing; monitor therapeutic response (eg, viral clearance) and consider therapeutic drug monitoring (if available) to guide further dosage adjustments (Ref).
Hemodialysis, intermittent (thrice weekly): Dialyzable (37% to 55%) (Ref):
Intravitreal: No data available. No dosage adjustment necessary as systemic absorption is likely to be limited (Ref).
IV: Induction and maintenance: 45 to 60 mg/kg/dose administered 3 times per week after hemodialysis (Ref). Consider starting at the lower end of the dosing range for treatment of herpes simplex virus and at the higher end for treatment of cytomegalovirus (CMV) (Ref). Some experts suggest therapeutic drug monitoring (Ref).
Peritoneal dialysis:
Intravitreal: No data available. No dosage adjustment necessary as systemic absorption is likely to be limited (Ref).
IV: 45 to 60 mg/kg/dose every 48 to 72 hours (Ref). Consider starting at the lower end of the dosing range for treatment of herpes simplex virus and at the higher end for treatment of CMV (Ref).
Note: Approximately one-third of a 60 mg/kg dose is removed by CAPD in 72 hours, and the presence of residual kidney function can significantly impact clearance (Ref). These data suggest optimal dosing interval for most patients is likely every 48 to 72 hours depending on patient’s residual kidney function; however, one case report recommended a dose of 45 mg/kg every 24 hours (Ref).
CRRT:
Note: Drug clearance is dependent on the effluent flow rate, filter type, and method of renal replacement. Recommendations are based on high-flux dialyzers and effluent flow rates of 20 to 25 mL/kg/hour (or ~1,500 to 3,000 mL/hour) and minimal residual kidney function unless otherwise noted. Patients should be closely monitored for therapeutic response (eg, viral clearance) and evidence of drug toxicity (eg, nephrotoxicity).
Intravitreal: No data available. No dosage adjustment necessary as systemic absorption is likely to be limited (Ref).
IV: No data available. Removal is likely based on drug characteristics and the extent of removal by hemodialysis; dose as for CrCl >0.5 to 0.6 mL/minute/kg. Dosage adjustments may be warranted based on therapeutic response (eg, viral clearance) or evidence of drug toxicity. Note: Case reports have described doses of up to 30 to 50 mg/kg every 12 hours for severe CMV disease (Ref).
PIRRT (eg, sustained, low-efficiency diafiltration):
Note: Drug clearance is dependent on the effluent flow rate, filter type, and method of renal replacement. Patients should be closely monitored for therapeutic response (eg, viral clearance) and evidence of drug toxicity (eg, nephrotoxicity).
Intravitreal: No data available. No dosage adjustment necessary as systemic absorption is likely to be limited (Ref).
IV: No data available. Removal is likely given drug characteristics and the extent of removal by hemodialysis; dose as for CrCl ≥0.4 to 0.5 mL/minute/kg. When scheduled dose falls on a PIRRT day, administer post PIRRT. Dosage adjustments may be warranted based on therapeutic response (eg, viral clearance) or evidence of drug toxicity (Ref).
There are no dosage adjustments provided in manufacturer’s labeling.
Refer to adult dosing.
(For additional information see "Foscarnet: Pediatric drug information")
Cytomegalovirus (CMV) disease, treatment: Limited data available:
Immunocompromised patients without HIV:
Infants, Children, and Adolescents: IV: Induction: 180 mg/kg/day in divided doses every 8 or 12 hours for at least 2 weeks; duration depends on degree of immunosuppression, site of infection, and clinical response. In recipients of hematopoietic cell transplant, induction therapy may be followed by maintenance therapy: 90 mg/kg/dose every 24 hours (Ref).
Patients with HIV:
Initial therapy:
Neurological disease (including CNS):
Infants, Children, and Adolescents: IV: Initial therapy: 180 mg/kg/day in divided doses every 8 or 12 hours in combination with ganciclovir until symptomatic improvement; optimal duration not established; follow with chronic maintenance therapy (Ref).
GI disease (esophagitis or colitis) (alternative agent): Adolescents: IV: 180 mg/kg/day in divided doses every 8 or 12 hours for 21 to 42 days or until resolution of symptoms (Ref).
Retinitis:
IV (alternative agent): Infants, Children, and Adolescents: Initial therapy: 180 mg/kg/day in divided doses every 8 or 12 hours for 14 to 21 days. Follow with chronic maintenance therapy. In adolescents with immediate sight-threatening lesions, use in combination with intravitreal therapy (ganciclovir or foscarnet). In infants and children with immediate sight-threatening disease, consider initial use in combination with ganciclovir; may also be considered as part of combination therapy for patients who fail monotherapy (Ref).
Intravitreal: Note: Recommended for adolescents with immediate sight-threatening lesions; use in combination with systemic therapy (Ref).
Adolescents: Initial therapy: Intravitreal: 2.4 mg/dose once weekly until lesion inactivity is achieved.
Chronic maintenance therapy (secondary prophylaxis): Note: Recommended for patients with HIV after most forms of CMV disease until immune reconstitution; only routinely recommended after GI disease if relapses have occurred (Ref).
Infants, Children, and Adolescents: IV: 90 to 120 mg/kg/dose every 24 hours. Duration of therapy dependent on multiple factors; in patients who have received ≥3 to 6 months of antiretroviral therapy (depending on age), may consider discontinuation based on additional factors (eg, disease site, age, CD4 cell count, clinical response, specialist input). If CD4 cell counts decrease below threshold after discontinuation, maintenance therapy should be resumed (Ref).
Cytomegalovirus (CMV), preemptive therapy in allogeneic hematopoietic cell transplant recipients: Limited data available:
Infants, Children, and Adolescents: Note: Requires serial blood monitoring for CMV. There is no standard recommendation for when to initiate; therapy is initiated when institutional-specific CMV positivity threshold is reached (Ref).
Induction: IV: 180 mg/kg/day in divided doses every 8 or 12 hours. Typically continued for ≥2 weeks and until indicator test is negative, or until viral load decreases; practice varies (Ref).
Maintenance: IV: 90 mg/kg/dose every 24 hours. Duration of treatment is patient- and center-specific; therapy may be continued (as secondary prophylaxis) following clearance to prevent recurrence in patients with continued infection risk (Ref).
Cytomegalovirus (CMV), prophylaxis in allogeneic hematopoietic cell transplant recipients (alternative agent): Limited data available:
Prophylactic therapy: Note: Primary prophylaxis is not routinely recommended; when utilized, typically administered from engraftment to 100 days post-transplant, though practice may vary (Ref).
Infants, Children, and Adolescents: IV: 90 mg/kg/dose every 24 hours (Ref).
Herpes simplex virus (HSV) infection, treatment: Limited data available: Note: Reserve for acyclovir-resistant HSV (Ref).
Infants and Children with HIV: IV: 120 mg/kg/day in divided doses every 8 or 12 hours. Duration depends on severity, infection site, and clinical response (Ref).
Adolescents with HIV: IV: 80 to 120 mg/kg/day in divided doses every 8 or 12 hours until clinical response (Ref).
Varicella zoster virus (VZV): Limited data available:
Disease unresponsive or resistant to acyclovir: Infants and Children with HIV: 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 (Ref).
Progressive outer retinal necrosis (zoster): Persons with HIV:
IV: Infants and Children: 180 mg/kg/day in divided doses every 12 hours as part of an appropriate combination regimen (Ref).
Intravitreal: Infants, Children, and Adolescents: 1.2 mg in 0.05 mL per dose, injected in the vitreum twice weekly; must be used in combination with systemic antiviral therapy (Ref).
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
Altered kidney function:
Indications other than cytomegalovirus (CMV) treatment: There are no pediatric-specific dosage adjustments available; based on experience in adults, dosage adjustment is suggested.
CMV treatment:
Note: Dosage adjustments are based on creatine clearance reported as mL/minute/kg, which is not a standard calculation; use caution. To determine mL/minute/kg: use SCr and bedside Schwartz equation or cystatin C and chronic kidney disease in children equation to calculate eGFR; multiply eGFR in mL/minute/1.73 m2 by patient's body surface area and divide by 1.73 m2; then divide by patient's weight in kg to obtain value in mL/minute/kg. Pediatric-specific dosage adjustments are only available for every-12-hour induction and every-24-hour maintenance dosing. Approaches may vary; presented dosage adjustments reflect one approach (Ref).
Infants, Children, and Adolescents (Ref):
|
CrCl (mL/minute/kg) |
If usual recommended dose is 90 mg/kg/dose every 12 hours (induction dose) |
If usual recommended dose is 90 mg/kg/dose every 24 hours (maintenance dose) |
|---|---|---|
|
>1.4 mL/minute/kg |
No dosage adjustment necessary |
No dosage adjustment necessary |
|
>1 to 1.4 mL/minute/kg |
70 mg/kg/dose every 12 hours |
70 mg/kg/dose every 24 hours |
|
>0.8 to 1 mL/minute/kg |
50 mg/kg/dose every 12 hours |
50 mg/kg/dose every 24 hours |
|
>0.6 to 0.8 mL/minute/kg |
80 mg/kg/dose every 24 hours |
80 mg/kg/dose every 48 hours |
|
>0.5 to 0.6 mL/minute/kg |
60 mg/kg/dose every 24 hours |
60 mg/kg/dose every 48 hours |
|
≥0.4 to 0.5 mL/minute/kg |
50 mg/kg/dose every 24 hours |
50 mg/kg/dose every 48 hours |
|
<0.4 mL/minute/kg |
Use not recommended |
Use not recommended |
Hemodialysis (HD): No pediatric-specific dosage adjustments are available. Foscarnet is highly removed by hemodialysis (up to ~38% in 2.5 hours HD with high-flux membrane in adults) (Ref).
There are no dosage adjustments provided in the manufacturer's labeling.
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.
• 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: 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. 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: 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: Indicated only for patients who are immunocompromised with cytomegalovirus retinitis and mucocutaneous acyclovir-resistant herpes simplex virus infection.
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
Solution (Foscarnet Sodium Intravenous)
6000 mg/250 mL (per mL): $1.73 - $2.27
Solution (Foscavir Intravenous)
6000 mg/250 mL (per mL): $2.27
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Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Solution, Intravenous:
Vocarvi: 24 mg/mL (250 mL)
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 (Ref).
Parenteral: 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.
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) (Ref). To mitigate nephrotoxicity risk, adequate hydration is recommended (eg, 10 to 20 mL/kg [maximum: 1,000 mL] of NS as appropriate prior to first dose, then 10 to 20 mL/kg of NS [maximum: 1,000 mL] as appropriate concurrently with subsequent doses, with adjustment of fluid amount based on patient-specific factors) (Ref).
Intravitreal: Administer undiluted (24 mg/mL) in appropriate sterile setting by health care professional experienced in administration of intravitreal ophthalmic injections. In published reports, solution was passed through a 0.22 micron filter prior to injection (Ref).
Cytomegalovirus retinitis, treatment: Treatment of cytomegalovirus (CMV) retinitis in patients with AIDS.
Herpes simplex virus: Treatment of acyclovir-resistant mucocutaneous herpes simplex virus (HSV) infection in patients who are immunocompromised.
Cytomegalovirus, nonretinitis tissue-invasive disease, treatment; Cytomegalovirus, transplant recipients (hematopoietic cell), preemptive therapy; Varicella zoster virus, progressive outer retinal necrosis
None known.
Note: Interacting drugs may not be individually listed below if they are part of a group interaction (eg, individual drugs within “CYP3A4 Inducers [Strong]” are NOT listed). For a complete list of drug interactions by individual drug name and detailed management recommendations, use the drug interactions program by clicking on the “Launch drug interactions program” link above.
Acyclovir-Valacyclovir: Foscarnet may increase nephrotoxic effects of Acyclovir-Valacyclovir. Management: Avoid concomitant use of foscarnet and acyclovir or valacyclovir, unless the expected benefits of combined treatment outweigh the risks. If combined, monitor renal function closely. Risk D: Consider Therapy Modification
Aminoglycosides: Foscarnet may increase nephrotoxic effects of Aminoglycosides. Management: Avoid concomitant use of foscarnet and aminoglycoside antibiotics, unless the expected benefits of combined treatment outweigh the risks. If combined, monitor renal function closely. Risk D: Consider Therapy Modification
Amphotericin B: Foscarnet may increase nephrotoxic effects of Amphotericin B. Management: Avoid concomitant use of foscarnet and amphotericin B, unless the expected benefits of combined treatment outweigh the risks. If combined, monitor renal function closely. Risk D: Consider Therapy Modification
CycloSPORINE (Systemic): Foscarnet may increase nephrotoxic effects of CycloSPORINE (Systemic). Management: Avoid concomitant use of foscarnet and systemic cyclosporine, unless the expected benefits of combined treatment outweigh the risks. If combined, monitor renal function closely. Risk D: Consider Therapy Modification
Haloperidol: QT-prolonging Agents (Indeterminate Risk - Caution) may increase QTc-prolonging effects of Haloperidol. Risk C: Monitor
Loop Diuretics: May increase 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 increase nephrotoxic effects of Methotrexate. Management: Avoid concomitant use of foscarnet and methotrexate, unless the expected benefits of combined treatment outweigh the risks. If combined, monitor renal function closely. Risk D: Consider Therapy Modification
Pentamidine (Systemic): May increase adverse/toxic effects 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 increase QTc-prolonging effects 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
Tacrolimus (Systemic): Foscarnet may increase nephrotoxic effects of Tacrolimus (Systemic). Management: Avoid concomitant use of foscarnet and systemic tacrolimus, unless the expected benefits of combined treatment outweigh the risks. If combined, monitor renal function closely. Risk D: Consider Therapy Modification
Talimogene Laherparepvec: Antiherpetic Antivirals may decrease therapeutic effects of Talimogene Laherparepvec. Risk C: Monitor
Vasopressin: Drugs Suspected of Causing Diabetes Insipidus may decrease therapeutic effects of Vasopressin. Specifically, the pressor and antidiuretic hormone effects of vasopressin may be decreased. Risk C: Monitor
Outcome data related to use of foscarnet in pregnancy are 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] 2024).
It is not known if foscarnet is present in breast milk.
Due to the potential for serious adverse reactions in the breastfeeding infant, the manufacturer recommends a decision be made whether to discontinue breastfeeding or to discontinue the drug, considering the importance of treatment to the mother.
Some products may contain sodium.
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 one 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)
Altered kidney function: 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.
