Foscarnet Side Effects

Not all side effects for foscarnet may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to foscarnet: intravenous solution

Along with their needed effects, medicines like foscarnet can sometimes cause serious side effects such as kidney problems; these are described below. Foscarnet may also decrease the amount of calcium in your blood, causing you to have a tingling sensation around your mouth, and pain or numbness in your hands and feet. If this occurs, especially while you are receiving the medicine, notify your health care professional immediately.

In addition to its needed effects, some unwanted effects may be caused by foscarnet. In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking foscarnet:

More common
  • Increased or decreased frequency of urination or amount of urine
  • increased thirst
Less common
  • Convulsions (seizures)
  • fever, chills, and sore throat
  • muscle twitching
  • pain at place of injection
  • pain or numbness in hands or feet
  • tingling sensation around mouth
  • tremor
  • unusual tiredness and weakness
  • Sores or ulcers on the mouth or throat, penis, or vulva

Some of the side effects that can occur with foscarnet may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common
  • 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


Renal impairment is the major toxicity of foscarnet. The most frequent adverse events reported during clinical trials included fever (65%), nausea (47%), anemia (33%), diarrhea (30%), abnormal renal function (27%), vomiting (26%), headache (26%), and seizures (10%). Adverse events classified as severe included death (14%), abnormal renal function (14%), bone marrow suppression (10%), anemia (9%), and seizures (7%).


Renal side effects have included dose-related renal impairment, which is the major toxicity of foscarnet and has occurred in up to 33% of patients. Acute renal failure, serum creatinine elevations greater than or equal to 2.9 mg/dL, renal tubular acidosis, and renal calculi have also been reported.

Renal adverse effects are due to acute tubular necrosis, possibly from deposition of foscarnet crystals in the renal tubules and capillaries. Renal failure as well as tubular dysfunction such as nephrogenic diabetes insipidus may result. The development of nephrotoxicity was most common during the third week of therapy in one study.

Nephrotoxicity is reversible in patients with previously adequate renal function. Hydration with 2.5 liters of normal saline per day beginning the day before foscarnet therapy has been shown to decrease the incidence of nephrotoxicity.


Gastrointestinal side effects have included nausea (47%), vomiting (26%), diarrhea (30%), anorexia (5% or more), and abdominal pain (5% or more). Constipation, dysphagia, dyspepsia, rectal hemorrhage, dry mouth, melena, flatulence, ulcerative stomatitis, and pancreatitis have been reported in 1% to 5% of patients. An isolated case of uvula and esophageal ulceration has been reported.


Hematologic side effects have included anemia (33%), neutropenia (17%), granulocytopenia (5% or more), and leukopenia (5% or more). Thrombocytopenia, platelet abnormalities, thrombosis, blood cell abnormalities, and lymphadenopathy have been reported in 1% to 5% of patients.

Nervous system

Nervous system side effects have included headache (26%) and seizures (10%). Paresthesia, dizziness, involuntary muscle contractions, hypoesthesia, neuropathy, and grand mal seizures have been reported in greater than or equal to 5% of patients. Tremor, ataxia, dementia, stupor, generalized spasms, sensory disturbances, meningitis, aphasia, abnormal coordination, leg cramps, and EEG abnormalities have been reported in 1% to 5% of patients. Risk factors for foscarnet-related seizures include low neutrophil count, central nervous system disease, impaired renal function, and electrolyte and metabolic abnormalities.


Metabolic disturbances have occurred in 15% to 40% of patients treated with foscarnet and include hypocalcemia, hypomagnesemia, hypokalemia, hyponatremia secondary to nephrogenic diabetes insipidus, and hypo- and hyperphosphatemia. More severe metabolic abnormalities have resulted in tremors, twitches, arrhythmias, parenthesis, and seizures. Dehydration, hypoproteinemia, syndrome of inappropriate antidiuretic hormone secretion (SIADH), and increased amylase and creatinine phosphokinase have been reported in less than 1% of patients. Hypercalcemia has also been reported.

Serum ionized calcium concentrations have been shown to decrease acutely in a dose-dependent manner following an infusion of foscarnet. Total calcium and phosphate levels were not significantly affected. Foscarnet is believed to complex with ionized calcium.


Other side effects have included fever (65%), and fatigue, rigors, asthenia, malaise, pain, infection, and sepsis in greater than or equal to 5% of patients.


Local side effects have included injection site pain and inflammation.


Dermatologic side effects have included rash and increased sweating in greater than or equal to 5% of patients. Pruritus, skin ulceration, seborrhea, erythematous rash, maculopapular rash, and skin discoloration have been reported in 1% to 5% of patients. Erythema multiforme, toxic epidermal necrolysis, eosinophilic folliculitis, and Stevens-Johnson syndrome have been reported during postmarketing experience.


Reversible cardiac dysfunction has been reported in one patient receiving foscarnet, who experienced shortness of breath, increased heart rate, and pulmonary edema, which reoccurred upon rechallenge. Serum electrolytes were within normal limits. Ventricular arrhythmia and QT interval prolongation have been reported during postmarketing experience.

Cardiovascular side effects have included hypertension, palpitations, ECG abnormalities, sinus tachycardia, first degree AV block, nonspecific ST-T segment changes, hypotension, flushing, cerebrovascular disorder in 1% to 5% of patients. Cardiac arrest, coma, and other cardiovascular complications have been reported in less than 1% of patients.


Hepatic side effects have included abnormal hepatic function, abnormal A-G ratio, increased SGPT, and increased SGOT in 1% to 5% of patients. Increased gamma glutamyl transpeptidase has been reported during postmarketing experience.


Musculoskeletal side effects have included arthralgia and myalgia in 1% to 5% of patients. Myopathy, myositis, muscle weakness, and rhabdomyolysis have been reported during postmarketing experience.


Oncologic side effects have included lymphoma-like disorder and sarcoma in 1% to 5% of patients.


Respiratory side effects have included coughing and dyspnea in greater than or equal to 5% of patients. Pneumonia, sinusitis, pharyngitis, rhinitis, respiratory disorders, respiratory insufficiency, pulmonary infiltration, stridor, pneumothorax, hemoptysis, and bronchospasm have been reported in 1% to 5% of patients.


Psychiatric side effects have included confusion and anxiety in greater than or equal to 5% of patients. Insomnia, somnolence, nervousness, amnesia, agitation, aggressive reaction, and hallucination have been reported in 1% to 5% of patients.


Ocular side effects have included eye abnormalities, eye pain, and conjunctivitis in 1% to 5% of patients.


Genitourinary side effects have included albuminuria, dysuria, polyuria, urethral disorder, urinary retention, urinary tract infections, and nocturia in 1% to 5% of patients, and hematuria in less than 1% of patients. Local irritation and ulceration of penile epithelium in male patients and vulvovaginal ulceration in a female patient have also been reported.

Penile ulcerations have been reported to occur after a median of 11 days of induction therapy and 30 days of maintenance therapy, and heal within six days of drug discontinuation. Ulceration has been reported more often in uncircumcised patients. Vulvar erosion may also occur but is less common. Penile ulceration is thought to result from local irritation by high concentrations of foscarnet in the urine. Good hygiene may help reduce irritation.


Foscarnet accumulates in teeth and bones of growing animals. Tooth enamel development has been affected in rats receiving foscarnet.

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