Foscarnet Side Effects

Medically reviewed by Drugs.com. Last updated on Mar 17, 2025.

Applies to foscarnet: intravenous solution.

Important warnings This medicine can cause some serious health issues

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.

Serious side effects of foscarnet

Along with its needed effects, foscarnet 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 side effects

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

Less common side effects

• 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

Rare side effects

• 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

Other side effects of foscarnet

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 side effects

• abdominal or stomach pain
• anxious feeling
• confusion
• dizziness
• headache
• loss of appetite
• nausea and vomiting
• unusual tiredness or weakness

For healthcare professionals

Applies to foscarnet: intravenous solution.

General adverse events

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]

Renal

• 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]

Metabolic

• 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]

Gastrointestinal

• 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]

Other

• 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]

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]

Hematologic

• 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]

Dermatologic

• 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]

Local

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

Cardiovascular

• 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]

Hepatic

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

Musculoskeletal

• 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]

Oncologic

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

Respiratory

• 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]

Psychiatric

• Common (1% to 10%): Depression, confusion, anxiety, insomnia, nervousness, agitation, aggression, hallucination
• Postmarketing reports: Mental status changes^[Ref]

Ocular

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

Genitourinary

• 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]

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]

Endocrine

• Uncommon (0.1% to 1%): Syndrome of inappropriate antidiuretic hormone secretion
• Postmarketing reports: Diabetes insipidus

Further information

Foscarnet side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer