Drug Interaction Report

MONITOR: Coadministration with other drugs that can reduce serum calcium may potentiate the risk of hypocalcemia associated with foscarnet. Foscarnet chelates with divalent metal ions and causes a dose-related reduction in ionized serum calcium. Hypocalcemia may occur in 15% to 30% of treated patients. Severe hypocalcemia (Trousseau's and Chvostek's signs) and fatalities have been reported rarely in postmarketing surveillance during use of foscarnet in combination with intravenous pentamidine. The interaction has not been reported with other drugs.

MANAGEMENT: Close monitoring is recommended during concomitant use of foscarnet with other drugs that are known to affect calcium concentrations. Serum creatinine and electrolyte levels should be assessed prior to initiating therapy and frequently during therapy. Patients should be advised to promptly notify their physician if they experience potential symptoms of hypocalcemia such as perioral tingling, numbness in extremities, and paresthesias.