foscarnet (Rx) - Foscavir, Phosphonoformic acid

Dosing Forms & Strengths

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

>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)

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

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)

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