Foscarnet Dosage
This dosage information may not include all the information needed to use Foscarnet safely and effectively. See additional information for Foscarnet.
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Usual Adult Dose for:
Usual Pediatric Dose for:
Additional dosage information:
Usual Adult Dose for CMV Retinitis
HIV/AIDS-infected patients:
Induction therapy: 90 mg/kg (90-120 minute infusion) every 12 hours or 60 mg/kg (minimum 1 hour infusion) every 8 hours over 2 to 3 weeks depending on clinical response.
Maintenance therapy: 90 mg/kg/day (2 hour infusion). Escalation to 120 mg/kg/day may be considered should early reinduction be required because of retinitis progression. Some patients who show excellent tolerance to foscarnet may benefit from initiation of maintenance treatment at 120 mg/kg/day earlier in their treatment.
Usual Adult Dose for Herpes Simplex - Mucocutaneous/Immunocompromised Host
Acyclovir-resistant infection:
Induction therapy: 40 mg/kg (minimum 1 hour infusion) every 8 or 12 hours for 2 to 3 weeks until healed.
Usual Adult Dose for Varicella-Zoster
Acyclovir-resistant infection in HIV-infected patients (n=5):
40 mg/kg (minimum 1 hour infusion) every 8 hours for 14 to 26 days.
Usual Pediatric Dose for CMV Retinitis
HIV/AIDS-infected patients:
Adolescents:
Induction therapy: 90 mg/kg (90 to 120 minute infusion) every 12 hours or 60 mg/kg (minimum 1 hour infusion) every 8 hours over 2 to 3 weeks depending on clinical response.
Maintenance therapy: 90 mg/kg/day (2 hour infusion). Escalation to 120 mg/kg/day may be considered should early reinduction be required because of retinitis progression. Some patients who show excellent tolerance to foscarnet may benefit from initiation of maintenance treatment at 120 mg/kg/day earlier in their treatment.
Usual Pediatric Dose for Herpes Simplex - Mucocutaneous/Immunocompromised Host
Acyclovir-resistant infection:
Adolescents:
Induction therapy: 40 mg/kg (minimum 1 hour infusion) every 8 or 12 hours for 2 to 3 weeks until healed.
Renal Dose Adjustments
Renal dose adjustments are based on creatinine clearance (mL/min/kg ) calculated according to a modified Cockcroft-Gault formula: (140-age) / (serum creatinine x 72), or actual 24-hour creatinine clearance divided by body weight.
CrCl < 0.4 mL/min/kg: Foscarnet is not recommended.
CrCl 0.4 to 0.5 mL/min/kg:
CMV Retinitis Induction: 50 mg/kg every 24 hours.
CMV Retinitis Maintenance: 50 mg/kg every 48 hours or 65 mg/kg every 48 hours.
HSV induction: 20 to 35 mg/kg every 24 hours.
CrCl 0.5-0.6 mL/min/kg:
CMV Retinitis Induction: 60 mg/kg every 24 hours.
CMV Retinitis Maintenance: 60 mg/kg every 48 hours or 80 mg/kg every 48 hours.
HSV induction: 25 to 40 mg/kg every 24 hours.
CrCl 0.6 to 0.8 mL/min/kg:
CMV Retinitis Induction: 40 mg/kg every 12 hours or 80 mg/kg every 24 hours.
CMV Retinitis Maintenance: 80 mg/kg every 48 hours or 105 mg/kg every 48 hours.
HSV induction: 35 mg/kg every 24 hours or 25 mg/kg every 12 hours.
CrCl 0.8 to 1 mL/min/kg:
CMV Retinitis Induction: 50 mg/kg every 12 hours.
CMV Retinitis Maintenance: 50 mg/kg or 65 mg/kg every 24 hours.
HSV induction: 20 to 35 mg/kg every 12 hours.
CrCl 1.0 to 1.4 mL/min/kg:
CMV Retinitis Induction: 45 mg/kg every 8 hours or 70 mg/kg every 12 hours.
CMV Retinitis Maintenance: 70 mg/kg or 90 mg/kg every 24 hours.
HSV induction: 30 mg/kg every 8 or 12 hours.
Liver Dose Adjustments
Data not available
Dose Adjustments
Patients who experience progression of retinitis while receiving foscarnet maintenance therapy may be retreated with the induction and maintenance regimens with a combination of foscarnet and ganciclovir.
Precautions
Do not administer foscarnet by rapid or bolus I V injection. The toxicity of foscarnet may be increased as a result of excessive plasma levels. Care should be taken to avoid unintentional overdose by carefully controlling the rate of infusion. Therefore, an infusion pump must be used. In spite of the use of an infusion pump, overdoses have occurred. Hydration to establish diuresis both prior to and during treatment is recommended to minimize renal toxicity, provided there are no clinical contraindications.
To avoid local irritation, foscarnet solutions must be infused into veins with sufficient blood flow to allow rapid dilution and distribution. Vulvovaginal and penile epithelium ulcerations have been reported, and may be due to the presence of foscarnet in the urine. Adequate hydration and good personal hygiene are recommended to minimize occurrence.
Serum electrolyte abnormalities, including hypocalcemia, decreased ionized serum calcium (which may not be reflected in total serum calcium), hypophosphatemia, hyperphosphatemia, hypomagnesemia, and hypokalemia have been associated with foscarnet treatment. The manufacturer recommends monitoring electrolytes two to three times per week during induction therapy with foscarnet, and at least once a week during maintenance therapy. Patients should be monitored for and advised to report possible symptoms of low ionized calcium, including perioral tingling, extremity numbness, and paresthesias. Clinicians should be prepared to treat electrolyte abnormalities, tetany, seizures, and cardiac disturbances.
Fatal and nonfatal seizures have resulted from electrolyte abnormalities. Risk factors for seizures include baseline renal impairment, low total serum calcium, and underlying CNS conditions.
Foscarnet commonly causes nephrotoxicity, thus patients receiving the drug should be monitored closely. Adequate hydration is recommended to decrease the incidence of renal toxicity. Dosage reductions are recommended for renally impaired patients. Caution is recommended in elderly patients who may have decreased renal function. Concomitant administration of other nephrotoxic drugs should be avoided.
Anemia and neutropenia have been reported in 33% and 17% of patients, respectively, in clinical trials. Foscarnet was discontinued in 1% due to neutropenia.
Patients should be advised that foscarnet is not a cure for CMV retinitis or mucocutaneous herpes simplex infections.
Safety and efficacy have not been established in pediatric patients. Foscarnet is deposited in bones and teeth, with greater deposition occurring in young and growing animals. It has adversely affected development of tooth enamel in rodents. Foscarnet should only be administered to pediatric patients if the potential benefit outweighs the risks.
Dialysis
CrCl < 0.4 mL/min/kg: Foscarnet is not recommended.
Other Comments
Foscarnet is administered by controlled IV infusion, either by using a central venous line or by using a peripheral vein. The standard 24 mg/mL solution may be used with or without dilution when using a central venous catheter for infusion. When a peripheral vein catheter is used, the 24 mg/mL solution must be diluted to 12 mg/mL with D5W or NS prior to administration to avoid local irritation of peripheral veins.
