Care must be taken to infuse solutions containing foscarnet sodium only into veins with adequate blood flow to permit rapid dilution and distribution to avoid local irritation (see DOSAGE AND ADMINISTRATION). Local irritation and ulcerations of penile epithelium have been reported in male patients receiving foscarnet sodium, possibly related to the presence of drug in the urine. Cases of male and female genital irritation/ulceration have been reported in patients receiving foscarnet sodium. Adequate hydration with close attention to personal hygiene may minimize the occurrence of such events.

Due to the sodium content of foscarnet sodium (240 micromoles (5.5 mg) of sodium per mL), avoid foscarnet sodium use when intravenous infusion of a large amount of sodium or water may not be tolerated (e.g., in patients with cardiomyopathy). Foscarnet sodium should also be avoided in patients on a controlled sodium diet.

Hematopoietic System

Anemia has been reported in 33% of patients receiving foscarnet sodium in controlled studies. Granulocytopenia has been reported in 17% of patients receiving foscarnet sodium in controlled studies; however, only 1% (2/189) were terminated from these studies because of neutropenia.

Information for Patients

CMV Retinitis: Patients should be advised that foscarnet sodium is not a cure for CMV retinitis, and that they may continue to experience progression of retinitis during or following treatment. They should be advised to have regular ophthalmologic examinations.

Mucocutaneous Acyclovir-Resistant HSV Infections: Patients should be advised that foscarnet sodium is not a cure for HSV infections. While complete healing is possible, relapse occurs in most patients. Because relapse may be due to acyclovir-sensitive HSV, sensitivity testing of the viral isolate is advised. In addition, repeated treatment with foscarnet sodium has led to the development of resistance associated with poorer response. In the case of poor therapeutic response, sensitivity testing of the viral isolate also is advised.

Effects on Ability to Drive and Use Machines: Adverse effects such as dizziness and convulsions may occur during foscarnet sodium therapy. Patients who experience seizures, dizziness, somnolence or other adverse reactions that could result in impairment, should be advised to avoid driving or operating machinery.

General: Patients should be informed that the major toxicities of foscarnet are renal impairment, electrolyte disturbances, and seizures, and that dose modifications and possibly discontinuation may be required. The importance of close monitoring while on therapy must be emphasized. Patients should be advised of the importance of reporting to their physicians symptoms of perioral tingling, numbness in the extremities or paresthesias during or after infusion as possible symptoms of electrolyte abnormalities. Patients should also be advised to promptly report any cardiac symptoms. Should such symptoms occur, the infusion of foscarnet sodium should be stopped, appropriate laboratory samples for assessment of electrolyte concentrations obtained, and a physician consulted before resuming treatment. The rate of infusion must be no more than 1 mg/kg/minute. The potential for renal impairment may be minimized by accompanying foscarnet sodium administration with hydration adequate to establish and maintain a diuresis during dosing.