Generic Name

Foscarnet Sodium

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Classification

FDA Approved Indications

• Treatment of cytomegalovirus (CMV) retinitis in immunocompromised patients
• Treatment of acyclovir-resistant herpes simplex virus (HSV) infections

Mechanism of Action

Foscarnet inhibits viral DNA polymerase by binding to its pyrophosphate binding site, thereby inhibiting viral DNA synthesis without requiring activation by viral kinase enzymes.

Dosage and Administration

Adult: Initial dose: 40 mg/kg every 8 hours for 14-21 days, administered intravenously. Dose adjustment based on renal function.

Pediatric: Dose varies; typically 90-180 mg/kg/day divided every 8 hours, depending on age and renal function.

Geriatric: Use with caution; renal function should be monitored closely due to increased risk of toxicity.

Renal Impairment: Dose adjustment required; typically, dosing interval is increased based on creatinine clearance.

Hepatic Impairment: No specific adjustments; hepatic impairment does not significantly affect pharmacokinetics.

Pharmacokinetics

Absorption: Not applicable; administered IV.

Distribution: Widely distributed throughout body tissues, crosses blood-brain barrier.

Metabolism: Not significantly metabolized; administered unchanged.

Excretion: Renal excretion; eliminated unchanged in urine.

Half Life: Approximately 3-7 hours; prolonged in renal impairment.

Contraindications

• hypersensitivity to foscarnet

Precautions

• use with caution in patients with renal impairment, electrolyte abnormalities, or concurrent nephrotoxic drugs; monitor renal function, electrolytes, and hydration status routinely.

Adverse Reactions - Common

• Renal toxicity (Common)
• Electrolyte disturbances (hypocalcemia, hypomagnesemia, hypokalemia) (Common)
• Nausea, vomiting, diarrhea (Common)

Adverse Reactions - Serious

• Seizures (Less common)
• Electrolyte imbalances leading to arrhythmias (Less common)
• Anemia, neutropenia (Less common)

Drug-Drug Interactions

• Nephrotoxic agents (e.g., aminoglycosides, amphotericin B)
• Cisplatin

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Patient/Family Teaching

• Report any signs of kidney problems (changes in urine, swelling).
• Maintain adequate hydration.
• Understand the importance of regular blood tests.

Special Considerations

Black Box Warnings:

• Foscarnet can cause significant renal toxicity and electrolyte disturbances.
• Seizures may occur, especially in patients with electrolyte abnormalities or renal failure.

Genetic Factors: None specified.

Lab Test Interference: May elevate serum creatinine and cause electrolyte disturbances, which require careful interpretation.

Overdose Management

Signs/Symptoms: Severe renal impairment, electrolyte disturbances, seizures.

Treatment: Discontinue drug, provide supportive care, correct electrolyte abnormalities, ensure adequate hydration, and consider renal support if necessary.

Storage and Handling

Storage: Store at room temperature, away from moisture and light.

Stability: Stable for the duration specified by manufacturer, check expiration date.