Classifications: antiviral;
Therapeutic: antiviral

Pregnancy Category: C


24 mg/mL injection


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).


CMV retinitis, mucocutaneous HSV, acyclovir-resistant HSV in immunocompromised patients.

Unlabeled Uses

Other CMV infections, herpes zoster infections in AIDS patients.


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.


  • Note: Dose must be adjusted for renal insufficiency. See package insert for specific dosing adjustment.

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.


Drug: aminoglycosides, amphotericin B, vancomycin may increase risk of nephrotoxicity. Etidronate, pamidronate, pentamidine (IV) may exacerbate hypocalcemia.


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

© 2006-2022 Last Updated On: 11/20/2022 (0)
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