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Foscavir Side Effects

Generic name: foscarnet

Medically reviewed by Last updated on Mar 22, 2022.

Note: This document contains side effect information about foscarnet. Some of the dosage forms listed on this page may not apply to the brand name Foscavir.

For the Consumer

Applies to foscarnet: intravenous solution


Intravenous route (Solution)

Renal impairment is the major toxicity of foscarnet. Frequent monitoring of serum creatinine, with dose adjustment for changes in renal function, and adequate hydration with administration of foscarnet is imperative. Seizures, related to alteration in plasma minerals and electrolytes, have been associated with foscarnet treatment. Therefore, patients must be carefully monitored for such changes and their potential sequelae. Mineral and electrolyte supplementation may be required. Foscarnet is indicated for use only in immunocompromised patients with cytomegalovirus retinitis and mucocutaneous acyclovir-resistant herpes simplex virus infections.

Side effects requiring immediate medical attention

Along with its needed effects, foscarnet (the active ingredient contained in Foscavir) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor or nurse immediately if any of the following side effects occur while taking foscarnet:

More common

  • Increased or decreased frequency of urination or amount of urine
  • increased thirst

Less common

  • Chills
  • convulsions
  • fever
  • muscle twitching
  • pain at the injection site
  • pain or numbness in hands or feet
  • tingling sensation around the mouth
  • tremor
  • unusual tiredness and weakness


  • Sores or ulcers on the mouth or throat, penis, or vulva

Incidence not known

  • Difficulty with breathing or swallowing
  • fainting
  • hives or welts, itching, or skin rash
  • irregular heartbeat recurrent
  • large, hive-like swelling on the face, eyelids, lips, tongue, throat, hands, legs, feet, or sex organs
  • nausea
  • reddening of the skin, especially around the ears
  • swelling of the eyes, face, or inside of the nose

Side effects not requiring immediate medical attention

Some side effects of foscarnet may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

For Healthcare Professionals

Applies to foscarnet: intravenous solution


Renal impairment was the major toxicity of this drug. The most frequent side effects reported during clinical trials included fever, nausea, anemia, diarrhea, abnormal renal function, vomiting, headache, and seizures. Severe side effects included death, abnormal renal function, bone marrow suppression, anemia, and seizures.[Ref]


Very common (10% or more): Renal impairment (up to 33%), abnormal renal function (up to 27%), increased serum creatinine

Common (1% to 10%): Altered renal function, decreased CrCl, increased BUN, acute renal failure, renal pain

Uncommon (0.1% to 1%): Renal tubular disorder

Frequency not reported: Increased serum creatinine to greater than 2.9 mg/dL, acute tubular necrosis, drug crystals in renal tubules and capillaries, nephrotoxicity

Postmarketing reports: Nephrogenic diabetes insipidus, renal tubular acidosis, renal calculus, renal tubular necrosis, crystal-induced nephropathy[Ref]

About 33% of AIDS patients with CMV retinitis who used this drug without adequate hydration reported significant renal impairment (serum creatinine at least 2 mg/dL). When administered with 1000 mL of normal saline or 5% dextrose solution, the incidence decreased to 12%.

Renal side effects were due to acute tubular necrosis, possibly from deposition of drug crystals in the renal tubules and capillaries. The development of nephrotoxicity was most common during the third week of therapy in 1 study.

Nephrotoxicity was reversible in patients with previously adequate renal function. Hydration with 2.5 liters of normal saline per day beginning the day before therapy decreased the incidence of nephrotoxicity.[Ref]


Very common (10% or more): Serum electrolyte changes, mineral and electrolyte imbalances, hypokalemia (up to 48%), hypocalcemia (up to 30%), hypomagnesemia (up to 30%), hypophosphatemia (up to 26%), decreased appetite, anorexia

Common (1% to 10%): Hyperphosphatemia, abnormal albumin to globulin ratio, hyponatremia, decreased weight, increased alkaline phosphatase, increased lactate dehydrogenase, acidosis, cachexia, thirst

Uncommon (0.1% to 1%): Dehydration, hypoproteinemia

Frequency not reported: Hypercalcemia., decreased serum ionized calcium levels[Ref]

The higher percentages of serum electrolyte changes (including hypokalemia, hypocalcemia, hypomagnesemia, hypophosphatemia, hyperphosphatemia) were reported in patients receiving hydration.

Serum ionized calcium levels have been shown to decrease acutely in a dose-dependent manner after an infusion of this drug. Total calcium and phosphate levels were not significantly affected. This drug is believed to complex with ionized calcium.

More severe metabolic abnormalities have resulted in tremors, twitches, arrhythmias, paresthesias, and seizures.[Ref]


Very common (10% or more): Nausea (up to 47%), diarrhea (up to 30%), vomiting (up to 26%)

Common (1% to 10%): Abdominal pain, constipation, dysphagia, dyspepsia, rectal hemorrhage, dry mouth, melena, flatulence, ulcerative stomatitis, pancreatitis

Uncommon (0.1% to 1%): Increased amylase

Frequency not reported: Uvula ulceration

Postmarketing reports: Esophageal ulceration[Ref]


In controlled trials, death was specifically attributed to this drug in 1 case; however, other drug complications (e.g., renal impairment, electrolyte abnormalities, seizures) may have contributed to patient deaths.[Ref]

Very common (10% or more): Fever/pyrexia (up to 65%), death (up to 14%), fatigue, asthenia, chills

Common (1% to 10%): Rigors, malaise, pain, infection, sepsis, chest pain, edema, influenza-like symptoms, bacterial infections, moniliasis, fungal infections, abscess, facial edema

Frequency not reported: Catheterization-related infection, hospitalization, drug accumulation in teeth and bones[Ref]


Very common (10% or more): Anemia (up to 33%), granulocytopenia (up to 17%), decreased hemoglobin

Common (1% to 10%): Marrow suppression, neutropenia, leukopenia, thrombocytopenia, platelet abnormalities, thrombosis, white blood cell abnormalities, lymphadenopathy

Uncommon (0.1% to 1%): Pancytopenia

Frequency not reported: Decreased absolute neutrophil count (ANC) to less than 0.5 x 10(9)/L, hemoglobin less than 7 g/dL[Ref]

Nervous system

Very common (10% or more): Headache (up to 26%), paresthesia, dizziness

Common (1% to 10%): Seizures/convulsion (including grand mal seizures), involuntary muscle contractions, hypoesthesia, neuropathy, tremor, ataxia, dementia, stupor, generalized spasms, sensory disturbances, meningitis, aphasia, abnormal coordination, leg cramps, electroencephalogram abnormalities, amnesia, somnolence, taste perversions, peripheral neuropathy

Uncommon (0.1% to 1%): Coma, other neurologic complications

Postmarketing reports: Encephalopathy[Ref]

Risk factors for drug-related seizures included underlying central nervous system conditions predisposing patients to seizures, impaired baseline renal function, and low total serum calcium. The rate of seizures did not increase with duration of therapy. At least 3 cases were reported with overdoses of this drug.[Ref]


Very common (10% or more): Rash

Common (1% to 10%): Increased sweating, pruritus, skin ulceration, seborrhea, erythematous rash, maculopapular rash, skin discoloration

Frequency not reported: Eosinophilic folliculitis

Postmarketing reports: Vesiculobullous eruptions, erythema multiforme, toxic epidermal necrolysis, Stevens-Johnson syndrome[Ref]

When toxic epidermal necrolysis or Stevens-Johnson syndrome was reported, patients were usually taking other agents associated with those reactions.[Ref]


Common (1% to 10%): Injection site pain, injection site inflammation[Ref]


Common (1% to 10%): Hypertension, palpitations, ECG abnormalities, sinus tachycardia, first degree atrioventricular block, nonspecific ST-T segment changes, hypotension, flushing, cerebrovascular disorder, thrombophlebitis

Uncommon (0.1% to 1%): Cardiac arrest, other cardiovascular complications

Frequency not reported: Reversible cardiac dysfunction, increased heart rate

Postmarketing reports: Ventricular arrhythmia, QT interval prolongation[Ref]

Reversible cardiac dysfunction was reported in a patient using this drug, who experienced shortness of breath, increased heart rate, and pulmonary edema, which reoccurred upon rechallenge. Serum electrolytes were within normal limits.

Thrombophlebitis in peripheral veins has been reported after infusion of undiluted drug solution.[Ref]


Common (1% to 10%): Abnormal hepatic function, increased ALT/SGPT, increased AST/SGOT, increased GGT[Ref]


Common (1% to 10%): Back pain, arthralgia, myalgia

Uncommon (0.1% to 1%): Increased creatine phosphokinase

Frequency not reported: Twitches

Postmarketing reports: Muscle disorders including myopathy, myositis, muscle weakness, rhabdomyolysis[Ref]


Common (1% to 10%): Lymphoma-like disorder, sarcoma[Ref]


Common (1% to 10%): Coughing, dyspnea, pneumonia, sinusitis, pharyngitis, rhinitis, respiratory disorders, respiratory insufficiency, pulmonary infiltration, stridor, pneumothorax, hemoptysis, bronchospasm

Frequency not reported: Pulmonary edema[Ref]


Common (1% to 10%): Depression, confusion, anxiety, insomnia, nervousness, agitation, aggression, hallucination

Postmarketing reports: Mental status changes[Ref]


Common (1% to 10%): Vision abnormalities, eye abnormalities, eye pain, conjunctivitis[Ref]


High levels of this drug are excreted in the urine and may be associated with significant irritation and ulceration in the genital area, especially after prolonged therapy.

Penile ulcerations have been reported to occur after a median of 11 days of induction therapy and 30 days of maintenance therapy, and healed within 6 days of drug discontinuation. Ulceration has been reported more often in uncircumcised patients.[Ref]

Common (1% to 10%): Albuminuria, dysuria, polyuria, urethral disorder, urinary retention, urinary tract infections, nocturia, genital discomfort/irritation and ulceration

Uncommon (0.1% to 1%): Hematuria

Frequency not reported: Local irritation/ulceration of penile epithelium, vulvovaginal ulceration, penile ulceration, vulvar erosion[Ref]


Uncommon (0.1% to 1%): Syndrome of inappropriate antidiuretic hormone secretion

Postmarketing reports: Diabetes insipidus


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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.