FOSCARNET
| FOSCARNET (fos'car-net) Foscavir Classifications: antiviral; Therapeutic: antiviral Pregnancy Category: C |
Availability
24 mg/mL injection
Action
Selectively inhibits the viral-specific DNA polymerases and reverse transcriptases of susceptible viruses, thus preventing elongation of the viral DNA chain.
Therapeutic Effect
Effective against cytomegalovirus (CMV), herpes simplex virus types 1 and 2 (HSV-1, HSV-2), human herpesvirus 6 (HHV-6), Epstein-Barr virus (EBV), and varicella-zoster virus (VZV).
Uses
CMV retinitis, mucocutaneous HSV, acyclovir-resistant HSV in immunocompromised patients.
Unlabeled Uses
Other CMV infections, herpes zoster infections in AIDS patients.
Contraindications
Hypersensitivity to foscarnet; pregnancy (category C), lactation.
Cautious Use
Kidney function impairment, cardiac disease; mineral and electrolyte imbalances, seizures, older adults. Safety and efficacy in children are not established.
Route & Dosage
| CMV Retinitis Adult: IV Induction 60 mg/kg q8h for 2–3 wk OR 90 mg/kg q12h for 2–3 wk Recurrent CMV Retinitis Adult: IV 90–120 mg/kg/d x 2 wk Acyclovir-Resistant HSV in Immunocompromised Patients Adult: IV 40 mg/kg q8–12h for up to 3 wk or until lesions heal Renal Impairment See package insert. |
Administration
- Note: Dose must be adjusted for renal insufficiency. See package insert for specific dosing adjustment.
| Intravenous PREPARE: Direct: Given undiluted (24 mg/mL) through a central line. For peripheral infusion, dilute to 12 mg/mL with D5W or NS. Do not give other IV solution or drug through the same catheter with foscarnet. ADMINISTER: Direct: ??Give at a constant rate not to exceed 1 mg/kg/min over the specified period of infusion with an infusion pump. Do not increase the rate of infusion or shorten the specified interval between doses.??Use prepared IV solutions within 24 h. INCOMPATIBILITIES Solution/additive: Ringer's lactate, acyclovir, amphotericin B, diazepam, digoxin, diphenhydramine, dobutamine, droperidol, ganciclovir, haloperidol, leucovorin, lorazepam, midazolam, pentamidine, phenytoin, prochlorperazine, promethazine, sulfamethoxazole/trimethoprim, TPN, trimetrexate, vancomycin. Y-site: Acyclovir, amphotericin B, diazepam, digoxin, diphenhydramine, dobutamine, droperidol, ganciclovir, haloperidol, leucovorin, lorazepam, midazolam, pentamidine, prochlorperazine, promethazine, sulfamethoxazole/trimethoprim, trimetrexate, vancomycin. |
- Prehydrate and continue daily hydration with 2.5 L of NS to reduce nephrotoxicity.
- Store according to manufacturer's directions.
Adverse Effects (≥1%)
CV: Thrombophlebitis if infused through a peripheral vein. CNS: Tremor, muscle twitching, headache, weakness, fatigue, confusion, anxiety. Endocrine: Hyperphosphatemia, hypophosphatemia, hypocalcemia. GI: Nausea, vomiting, diarrhea. Urogenital: Penile ulceration. Hematologic: Anemia, leukopenia, thrombocytopenia. Renal: Nephrotoxicity (acute renal failure, tubular necrosis). Skin: Fixed drug eruption, rash.Diagnostic Test Interference
May cause increase or decrease in serum calcium, phosphorus, and magnesium. Decreases Hct and Hgb. Increased serum creatinine.
Interactions
Drug: aminoglycosides, amphotericin B, vancomycin may increase risk of nephrotoxicity. Etidronate, pamidronate, pentamidine (IV) may exacerbate hypocalcemia.Pharmacokinetics
Onset: 3–7 d. Duration: Relapse usually occurs 3–4 wk after end of therapy. Distribution: 3–28% of dose may be deposited in bone; variable penetration into CSF; crosses placenta; distributed into breast milk. Metabolism: Not metabolized. Elimination: 73–94% in urine. Half-Life: 3–4 h.Nursing Implications
Assessment & Drug Effects
- Monitor for cardiac arrhythmias, especially in presence of known cardiac abnormalities.
- Lab tests: Periodic CBC, serum electrolytes, serum creatinine, and creatinine clearance throughout therapy.
- Monitor serum creatinine and creatinine clearance values. Drug dose will be decreased in response to decreased clearance.
- Monitor for electrolyte imbalances.
- Monitor for seizures and take appropriate precautions.
- Question patients regarding local irritation of the penile or vulvovaginal epithelium. If either occurs, increase hydration and better personal hygiene.
Patient & Family Education
- Report perioral tingling, numbness, and paresthesia to physician immediately.
- Understand that drug is not a cure for CMV retinitis; regular ophthalmologic exams are necessary.
- Note: Good hydration is important to maintain adequate output of urine.
Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; 
Canadian drug name; 
Prototype drug