The Food and Drug Administration (FDA) has added a “black box” warning to the label for Plavix® (clopidogrel), an anticlotting medication. The warning relates to patients who do not effectively metabolize the drug (i.e., “poor metabolizers”) and, therefore, may not receive the full benefits of the drug.
Plavix is prescribed to reduce the risk of heart attack, unstable angina, stroke, and cardiovascular death in patients with cardiovascular disease. It works by decreasing the activity of blood cells called platelets, making them less likely to form blood clots. Plavix is inactive until enzymes in the liver (particularly CYP2C19) metabolize it to its active form. Patients who are poor metabolizers of the drug do not effectively convert Plavix to its active form; these patients may not receive the full benefits of the drug. It is estimated that 2% to 14% of the population are poor metabolizers.
The warning also includes the following information:
- Warn about reduced effectiveness in patients who are poor metabolizers.
- Inform healthcare professionals that tests are available to identify genetic differences in CYP2C19 function.
- Advise healthcare professionals to consider use of other antiplatelet medications or alternative dosing strategies for Plavix in patients identified as poor metabolizers.
- Healthcare professionals should note that an appropriate dose regimen for patients who are poor metabolizers has not been established in clinical outcome trials.
- Advise doctors of genetic tests that can identify patients who are likely to be poor metabolizers.
The FDA is urging patients not to stop taking Plavix unless told to do so by their healthcare providers.