Foscarnet Disease Interactions

Foscarnet is nephrotoxic. Foscarnet crystals may deposit in renal tubules and capillaries, sometimes causing acute tubular necrosis and renal failure. Foscarnet may also concentrate in the urine and cause penile or vulvovaginal irritation. Adequate hydration is crucial to minimize the risk of renal damage and genital ulcerations. Generally, foscarnet should be administered by an infusion pump over 1 to 2 hours accompanied by hydration. The manufacturer recommends 750 to 1000 mL of normal saline or 5% dextrose solution prior to the first infusion of foscarnet to establish diuresis, then 500 mL (for 40 to 60 mg/kg dose of foscarnet) or 750 to 1000 mL (for 90 to 120 mg/kg dose of foscarnet) of hydration fluid concurrently with each subsequent foscarnet infusion. Patients who are dehydrated may be at increased risk for the development of nephrotoxicity and may benefit from additional hydration if tolerated.

Foscarnet may cause electrolyte disturbances, including hypocalcemia, hypo- or hyperphosphatemia, hypomagnesemia, and hypokalemia. Ionized serum calcium may also demonstrate a dose-dependent (and possibly rate-dependent) decrease that may not be reflected in total serum calcium. Patients should be instructed to report symptoms of low ionized calcium such as perioral tingling, numbness in the extremities, and paresthesias. Other electrolyte-related complications include tetany, seizures, and cardiac disturbances. Therapy with foscarnet should be administered cautiously in patients with preexisting fluid and electrolyte imbalance and those with underlying cardiac or neurologic abnormalities. Serum electrolyte levels should be closely monitored and managed in all patients treated with foscarnet.

Foscarnet is eliminated primarily by the kidney. Patients with renal impairment may be at greater risk for dose-limiting nephrotoxicity and other adverse effects of foscarnet due to decreased drug clearance. Renal function should be closely monitored in all patients receiving therapy with foscarnet, and the dosage adjusted based on serum creatinine. Hydration is recommended to reduce the risk of nephrotoxicity. The manufacturer recommends 750 to 1000 mL of normal saline or 5% dextrose solution prior to the first infusion of foscarnet to establish diuresis, then 500 mL (for 40 to 60 mg/kg dose of foscarnet) or 750 to 1000 mL (for 90 to 120 mg/kg dose of foscarnet) of hydration fluid concurrently with each subsequent foscarnet infusion. Foscarnet should be used with caution in patients with abnormal renal function because reduced plasma clearance of foscarnet will result in elevated plasma levels. Foscarnet dosing must be individualized according to the patient's renal function status. The use of foscarnet is not recommended in patients with severe renal impairment indicated by a CrCl < 0.4 mL/min/kg and in those patients undergoing hemodialysis because dosage guidelines have not been established.

The use of foscarnet is associated with hematologic toxicities, most commonly anemia and granulocytopenia. Thrombocytopenia has been reported rarely. Therapy with foscarnet should be administered cautiously in patients with preexisting blood dyscrasias or bone marrow suppression. Routine blood counts are recommended.