Boxed warning for clopidogrel: reduced effects for certain patients

A boxed warning was added to the label for clopidogrel (Plavix) to warn of reduced effectiveness in patients who metabolize the drug poorly, the FDA said last week.

Tests are available to identify genetic differences that may affect metabolic ability, and health care professionals should consider using other medications or alternative clopidogrel dosing strategies in patients identified as poor metabolizers, the FDA said. Although a higher dose regimen (600 mg loading dose followed by 150 mg once daily) in poor metabolizers increases antiplatelet response, an appropriate dose regimen for poor metabolizers hasn't been established in a clinical outcome trial, the agency said.

It is estimated that 2% to 14% of the population are poor metabolizers, the FDA said. The agency added information about this subset of patients to the drug's label in May 2009.