Dosing and uses of Foscavir Injection, Phosphonoformic acid (foscarnet)
Adult dosage forms and strengths
injectable solution
- 2.4g/100mL
CMV Retinitis
Patients with AIDS: Combination therapy with ganciclovir indated for patients who have relapsed following monotherapy with either foscarnet or ganciclovir
Induction: 60 mg/kg q8hr IV x14-21 days; infuse IV over at least 60 min
Maintenance: 90-120 mg/kg IV qDay; infuse IV over at least 60-90 min
Herpes Simplex
Indicated for Herpes simplex in patients with acyclovir resistance who are immunocompromised
Option 1: 40 mg/kg IV q8hr x14-21 days; infuse IV over at least 60 min
Option 2: 40-60 mg/kg IV q12hr x14-21 days; infuse IV over at least 60 min
Other Information
Administer by slow IV infusion
Prehydrate with 750-1000 mL NS or D5W before first infusion to decrease risk for nephrotoxicity
See prescribing information for dose adjustments for CrCl <1.4 mL/min/kg
Pediatric dosage forms and strengths
<18 years old: Safety and efficacy not established
Foscavir Injection, Phosphonoformic acid (foscarnet) adverse (side) effects
>10%
Fever (65%)
Nausea (47%)
Anemia (33%)
Vomiting (33%)
Diarrhea (30%)
Abnormal renal function/decreased CrCl (27%)
Headache (26%)
Seizures (10%)
1-10%
Fatigue
Depression
Confusion
Anxiety
Dizziness
Hypoesthesia
Malaise
Rash
Electrolyte imbalance (especially potassium, calcium, magnesium, and phosphorus)
Leukopenia
Neutropenia
Postmarketing reports
Esophageal ulceration, renal tubular acidosis, renal tubular necrosis, and crystal-induced nephropathy
Warnings
Black box warnings
Renal impairment is the major toxicity; reduce nephrotoxicity risk by IV prehydration with normal saline
Monitor serum creatinine level, and, if indicated, adjust dose according to renal impairment
Seizures, related to alterations in plasma minerals and electrolytes, reported; mineral and electrolyte supplementation may be required
Indicated for use only in immunocompromised patients with cytomegalovirus (CMV) retinitis and mucocutaneous acyclovir-resistant herpes simplex virus (HSV) infections
Contraindications
Hypersensitivity
Cautions
Caution with renal impairment
Do not administer by rapid or bolus IV injection; use infusion pump
May be associated with changes in serum electrolytes changes including hypocalcemia, hypo- or hyperphosphatemia, hypomagnesemia, or hypokalemia
Electrolyte abnormalities may increase risk of seizures
Due to sodium content of foscarnet (240 micromoles (5.5 mg) of sodium per mL); avoid foscarnet use when IV infusion of large amount of sodium or water may not be tolerated (e.g. in patients with cardiomyopathy); avoid foscarnet use in patients on a controlled sodium diet
Pregnancy and lactation
Pregnancy category: C
Lactation: not known if excreted in breast milk, do not nurse
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Foscavir Injection, Phosphonoformic acid (foscarnet)
Mechanism of action
Inhibits activity of pyrophosphate binding site on virus-specific DNA polymerases and reverse transcriptases; active against CMV, HSV-1, and HSV-2
Absorption
Peak Plasma Concentration: 589 µM (60 mg/kg q8hr), 623 µM (90 mg/kg q12hr)
Distribution
Protein Bound: 14-17%
Volume of distribution: 0.41 L/kg (60 mg/kg q8hr), 0.52 L/kg (90 mg/kg q12hr)
Elimination
Half-life: 4 hr (60 mg/kg q8hr); 3.3 hr (90 mg/kg q12hr)
Dialyzable: Not evaluated
Renal clearance: 5.6 L/hr (60 mg/kg q8hr), 6.4 L/hr (90 mg/kg q12hr)
Total body clearance: 6.2 L/hr (60 mg/kg q8hr); 7.1 L/hr (90 mg/kg q12hr)
Administration
IV Incompatibilities
Y-site: acyclovir, amphotericin B, diazepam, digoxin, diphenhydramine, dobutamine, droperidol, ganciclovir, haloperidol, leucovorin, lorazepam, midazolam, pentamidine, phenytoin, prochlorperazine edisylate, promethazine, TMP-SMX
IV Compatabilities
Solution: D5W, Ns
Additive: KCL
Y-site (partial list): aldesleukin, amikacin, aminophylline, ampicillin, aztreonam, most cephalosporins, clindamycin, fluconazole, furosemide, heparin, metronidazole, morphine, tobramycin, vancomycin (maybe vancomycin concentration dependant)
IV Preparation
Should be diluted in D5W or NS & transferred to PVC containers
For peripheral line administration, dilute to 12 mg/mL with D5W or Ns
For central line administration, may administer undiluted
IV Administration
Use an infusion pump, not exceeding 1 mg/kg/min
Adult induction doses of 60 mg/kg are administered over a minimum 1 hr
Adult maintenance doses of 90-120 mg are infused over 2 hr
Storage
Store at room temp
Protect from temperatures >40°C and from freezing
