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Foscarnet Sodium

( Phosphonoformic Acid )

Pronunciation: foss-CAR-net SO-dee-uhm
Class: Antiviral agent

Trade Names

Foscarnet Sodium
- Injection 24 mg/mL


Inhibits replication of all known herpes viruses, including cytomegalovirus (CMV), herpes simplex virus types 1 and 2 (HSV-1, HSV-2), human herpes virus 6 (HHV-6), Epstein-Barr virus (EBV) and varicella-zoster virus (VZV).

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C max is about 589 to 623 mcmol. C min is about 63 to 114 mcmol.


Protein binding is 14% to 17%. The drug deposits into the bone. Vd is about 0.41 to 0.52 L/kg.


Terminal t 1/ 2 is about 87.5 h. Systemic clearance is about 6.2 to 7.1 L/h and Cl R is about 5.6 to 6.4 L/h. Plasma t 1/ 2 is about 4 h.

Special Populations

Renal Function Impairment

Ccr of 50 to 80 mL/min has a Cl of about 1.33 mL/min/kg and a plasma t 1/ 2 of about 3.35 h. Ccr of 25 to 49 mL/min has a Cl of about 0.46 mL/min/kg and a plasma t 1/ 2 of about 13 h. Ccr of 10 to 24 mL/min has a Cl of 0.43 mL/min/kg and plasma t 1/ 2 about 25.3 h.

Indications and Usage

Treatment of CMV retinitis in patients with AIDS; treatment of acyclovir-resistant mucocutaneous HSV infections in immunocompromised patients; combination therapy with ganciclovir for patients who have relapsed after monotherapy with either drug.


Standard considerations.

Dosage and Administration

CMV Retinitis


Initial dose

60 mg/kg/dose at constant rate over at least 1 h every 8 h for 2 to 3 wk. Adjust for clinical response and renal function.

Maintenance dose

90 mg/kg/day infused over 2 h, individualized; max maintenance dose is 120 mg/kg/day.

HSV Infections


Initial dose

40 mg/kg/dose (min, 1 h infusion) every 8 or 12 h for 2 to 3 wk or until healed.


90 mg/kg/day given as an IV infusion over 2 h, individualized; max maintenance dose is 120 mg/kg/day.

General Advice

  • Administer by IV infusion only, at rate not to exceed 1 mg/kg/min. Use infusion pump to prevent rapid or bolus injection.
  • When administering through central vein, 24 mg/mL solution may be used. In peripheral veins, dilute with D5W or normal saline to 12 mg/mL.
  • Administer only with normal saline or D5W; incompatible with many drugs and supplements.


Use prepared solutions within 24 h of first entry into sealed bottle.

Drug Interactions

Nephrotoxic drugs

Elimination of foscarnet may be impaired by drugs that inhibit renal tubular secretion. Increased potential for nephrotoxicity with aminoglycosides, amphotericin B, and IV pentamidine.


Concomitant IV pentamidine may cause hypocalcemia.


Increased risk of anemia.


Do not give other drugs or supplements via same IV catheter.

Laboratory Test Interactions

None well documented.

Adverse Reactions


Hypertension; palpitations; ECG abnormalities including sinus tachycardia, first-degree heart block, nonspecific ST-T segment changes; hypotension; flushing; cerebrovascular disorder.


Headache; paresthesia; dizziness; involuntary muscle contractions; hypoesthesia; neuropathy; seizures; depression; confusion; anxiety; tremor; ataxia; dementia; stupor; generalized spasms; sensory disturbances; meningitis; aphasia; abnormal coordination; leg cramps; EEG abnormalities; insomnia; somnolence; nervousness; amnesia; agitation; aggressive reaction; hallucination.


Rash; increased sweating; pruritus; skin ulceration; seborrhea; erythematous or maculopapular rash; skin discoloration; facial edema.


Vision abnormalities; eye pain; conjunctivitis; sinusitis; rhinitis; taste perversions; pharyngitis.


Anorexia; nausea; diarrhea; vomiting; abdominal pain; constipation; dysphagia; dyspepsia; rectal hemorrhage; dry mouth; melena; flatulence; ulcerative stomatitis; pancreatitis.


Alterations in renal function, including decreased Ccr, abnormal renal function; albuminuria; dysuria; polyuria; urethral disorder; urinary retention; UTI; acute renal failure; nocturia; abnormal albumin-globulin ratio; increased AST and ALT.


Anemia; bone marrow suppression; granulocytopenia; leukopenia; thrombocytopenia; platelet abnormalities; thrombosis; WBC abnormalities; lymphadenopathy.


Mineral and electrolyte imbalances, including hypo- or hypercalcemia, hypokalemia, hypomagnesemia, hypo- or hyperphos-phatemia, hyponatremia; decreased weight; increased alkaline phosphatase, LDH, BUN; acidosis.


Coughing; dyspnea; pneumonia; respiratory disorders or insufficiency; pulmonary infiltrates; stridor; pneumothorax; hemoptysis; bronchospasm.


Fever; fatigue; rigors; asthenia; malaise; arthralgia or myalgia; cachexia; thirst; infection; sepsis; death; back or chest pain; edema; influenza-like symptoms; abscess; lymphoma-like disorders; sarcoma; injection site pain or inflammation.




Major toxicity. Frequent serum creatinine monitoring with dose adjustments for changes in renal function and adequate hydration is essential.

Seizures related to levels of minerals and electrolytes. May require supplementation.


Category C .




Safety and efficacy not studied. Drug is deposited in teeth and bone.

Renal Function

If Ccr drops below 0.4 mL/min/kg, discontinue drug. Ensure that baseline renal function tests have been obtained before beginning therapy, and repeat 2 to 3 times/wk during induction therapy and 1 to 2 times/wk during maintenance therapy.

Mineral and electrolyte imbalances

Patients, especially those on concomitant drugs known to influence serum minerals or electrolytes or those with cardiac or neurological abnormalities, may experience changes in electrolytes (eg, calcium, potassium, magnesium, phosphate) that could cause cardiac disturbances or seizures. Replacement therapy may be needed.

Ensure that baseline serum electrolyte levels (eg, calcium, magnesium, potassium, phosphate) have been obtained before beginning therapy, and repeat 2 to 3 times/wk during induction therapy and 1 to 2 times/wk during maintenance therapy.

If symptoms of electrolyte imbalance occur, infusion may need to be discontinued and electrolyte supplementation initiated.

Toxicity/local irritation

Infuse into veins with adequate blood flow to permit rapid dilution and distribution and avoid local irritation. Drug is excreted in urine and may cause irritation or ulceration of penile or vulvovaginal epithelium.



Electrolyte disturbances, paresthesia, renal dysfunction, seizures, coma.

Patient Information

  • Emphasize that drug does not cure CMV retinitis but may help prevent worsening of symptoms.
  • Explain that good hygiene and drinking plenty of fluids may help reduce risk of genital irritation or ulceration.
  • Instruct patient to report the following symptoms to health care provider: perioral tingling, numbness in extremities, paresthesia, fever, nausea, diarrhea, vomiting, headache, increased or decreased frequency or amount of urination, other bothersome side effects.
  • Caution patient not to take any OTC medications without consulting health care provider. Explain that serious drug interactions may result.

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