Data on metabolic acidosis prompt alert on zonisamide.

Serum bicarbonate levels should be checked in patients before initiating treatment with the antiepileptic drug zonisamide because of an association between the drug and metabolic acidosis, according to an alert issued by the Food and Drug Administration.

Serum bicarbonate should also be monitored during treatment even if patients do not have any symptoms of metabolic acidosis, the FDA advised.

The FDA's recommendations are based on the agency's review of updated clinical data, which indicate that treatment with zonisamide can cause metabolic acidosis in some patients. The risk may be elevated in patients with renal disease and other conditions or other treatments that cause a predisposition to metabolic acidosis, and "appears to be more frequent and severe in younger patients," the alert said. Zonisamide, which is marketed as Zonegran by Eisai Inc. and is available in generic formulations, is approved as adjunctive therapy in the treatment of partial seizures in adults with epilepsy.

Although patients who have developed metabolic acidosis have generally developed it early during treatment with zonisamide, the condition can occur at any time during treatment.

If a patient on zonisamide develops metabolic acidosis and it persists, clinicians should consider either reducing the dose or discontinuing treatment by tapering the drug, "and modifying the patient's antiepileptic treatment as appropriate." Alkali treatment should be considered "if the decision is made to continue patients with metabolic acidosis on zonisamide," the FDA advised.

Adverse events associated with zonisamide can be reported to the FDA at 800-FDA-1088, or www.fda.gov/medwatch/report/hcp.htm. A link to the advisory is available at www.fda.gov/cder/drug/InfoSheets/HCP/zonisamide HCP.htm.