Foscarnet Note: Controlling Calcium Depletion

The antiviral foscarnet, used in Europe for several years, is coming into wider U. S. use to treat acyclovir-resistant herpes, and also to treat CMV retinitis when ganciclovir fails. The drug is given intravenously. A patient called our attention to certain side effects of the drug, and their successful management in several patients by his physicians at New York University. This information may not be widely known.

Foscarnet can produce an abnormally low level of ionized calcium in the blood, which can cause symptoms including seizures, leg cramps, nausea, dizziness, and tingling in the feet and fingers. The standard blood test for calcium often gives a normal value; to diagnose the problem, it is necessary to test for ionized calcium, which most large medical laboratories can do.

When this problem occurs, it has been managed successfully by giving intravenous calcium, before giving the foscarnet. It is very important to properly flush the catheter after giving the calcium -- which otherwise could harden and destroy the catheter.

For more information, physicians administering foscarnet can call Douglas Dieterich, M. D., at New York University Medical Center, 212/986-3330.

[Note: The most serious side effect of foscarnet is kidney toxicity. Certain precautions, such as making sure the patient has enough water, usually with intravenous hydration, are necessary to reduce this risk. Any problem which results in nausea, vomiting, or diarrhea can lead to dehydration and make people especially vulnerable to kidney toxicity.]