Foscarnet sodium (phosphonoformic acid)

headache, seizures,fatigue, malaise, asthenia, paresthesia, dizziness, hypoes­thesia, neuropathy, tremor, ataxia, generalized spasms, dementia, stupor, se…

HOW SUPPLIED

Injection: 24 mg/ml in 250- and 500-ml bottles

ACTION

Inhibits all known herpesviruses in vitro by blocking the pyrophosphate binding site on DNA polymerases and reverse transcriptases

INDICATIONS & DOSAGE

CMV retinitis in patients with AIDS –

Adults: Initially, 60 mg/kg I.V. as an induction treatment in patients with normal renal function. Administer q 8 hours for 2 to 3 weeks, depending on clinical response. Follow with a maintenance infusion of 90 to 120 mg/kg daily. Or, 90 mg/kg I.V q 12 hours is used for induction.

Acyclovir-resistant HSV infections –

Adults: 40 mg/kg I.V. over I hour q 8 to 12 hours for 2 to 3 weeks or until healed.

Dosage adjustment: Refer to package insert for very specific dose adjustments. Dosage must be adjusted when creatinine clearance is below 1.5 ml/minute/kg. If creatinine clearance falls below 0.4 mi/minute/kg, discontinue drug.

ADVERSE REACTIONS

CNS: headache, seizures,fatigue, malaise, asthenia, paresthesia, dizziness, hypoes­thesia, neuropathy, tremor, ataxia, generalized spasms, dementia, stupor, sensory disturbances, meningitis, aphasia, abnormal coordination, EEG abnormalities, depression, confusion, anxiety, insomnia, somnolence, nervousness, amnesia, agitation, aggressive reaction, hallucinations.

CV: hypertension, palpitations, ECG abnormalities, sinus tachycardia, cerebrovascular disorder, first-degree AV block, hypotension, flushing, edema.

EENT: visual disturbances, taste perversion, eye pain, conjunctivitis, sinusitis, pharyngitis, rhinitis.

GI: nausea, diarrhea, vomiting, abdominal pain, anorexia, constipation, dysphagia, rectal hemorrhage, dry mouth, dyspepsia, melena, flatulence, ulcerative stomatitis, pancreatitis.

GU: abnormal renalfunction, decreased creatinine clearance and increased serum creatinine levels, albuminuria, dysuria, polyuria, urethral disorder, urine retention, urinwy tract infections, acute renal failure, candidiasis.

Hematologic: anemia, granulocytopenia, leukopenia, bone marrow suppression, thrombocytopenia, platelet abnormalities, thrombocytosis, WBC count abnormalities, lymphadenopathy.

Hepatic: increased liver enzymes; increased serum bilirubin, alkaline phosphatase, ALT, and AST levels; abnormal hepatic function.

Metabolic: hypokalemia, hypomagnesemia, hypophosphatemia or hyperphosphatemia, hypocalcemia, hyponatremia.

Musculoskeletal: leg cramps, arthralgia, myalgia, back or chest pain.

Respiratory: cough, dyspnea, pneumonitis, respiratory insufficiency, pulmonary infiltration, stridor, pneumothorax, bronchospasm, hemoptysis, flulike symptoms.

Skin: rash, diaphoresis, pruritus, skin ulceration, erythematous rash, seborrhea, skin discoloration, facial edema.

Other: death, fever, pain, sepsis, rigors, inflammation and pain at infusion site, lymphoma-like disorder, sarcoma, bacterial or fungal infections, abscess. INTERACTIONS

Drug-drug. Nephrotoxic drugs (such as aminoglycosides, amphotericin B): increased risk of nephrotoxicity. Avoid concomitant use.

Pentamidine: increased risk of nephrotoxicity; severe hypocalcemia has also been reported. Avoid concomitant use. Zidovudine: possible increased incidence or severity of anemia. Blood counts must be monitored.

EFFECTS ON DIAGNOSTIC TESTS

None reported.

CONTRAINDICATIONS

Contraindicated in patients with hyper­sensitivity to drug.

SPECIAL CONSIDERATIONS

Use cautiously and with reduced dosage in patients with abnormal renal function. Because drug is nephrotoxic, it can worsen renal impairment. Some degree of nephrotoxicity occurs in most patients treated with drug.

Because drug is highly toxic and toxicity is probably dose-related, always use the lowest effective maintenance dose during therapy.

Creatinine clearance is monitored frequently during therapy because of drug’s adverse effects on renal function. A baseline 24-hour creatinine clearance is recommended, followed by regular determinations two to three times weekly during induction and at least once every 1 to 2 weeks during maintenance.

Because drug can alter serum electrolytes, levels are monitored using a schedule similar to that established for creatinine clearance. The patient is assessed for tetany and seizures associated with abnormal electrolyte levels.

The patient’s hemoglobin and hematocrit levels must be monitored. Anemia is common (in up to 33% of patients treated with drug). It may be severe enough to require transfusions.

Keep in mind that drug administration is associated with a dose-related transient decrease in ionized serum calcium, which may not always be reflected in patient’s laboratory values.

I. V. administration

An infusion pump is used to administer foscarnet. To minimize renal toxicity, patient must be adequately hydrated before and during the infusion.

Induction treatment is administered over 1 hour; maintenance infusions over 2 hours.

Alert: Don’t exceed the recommended dosage, infusion rate, or frequency of administration. All doses must be individualized according to patient’s renal function.

Patient teaching

Adequate hydration throughout therapy is important.

Report perioral tingling, numbness in the extremities, and paresthesia.

Alert health care provider if discomfort occurs at I.V. insertion site.