Plavix Not Effective in All Patients, FDA Warns

<"">Plavix will now bear a new Black Box Warning alerting doctors and patients that it may be less effective in people who cannot metabolize the drug to convert it to its active form. A Black Box Warning is the Food & Drug Administration’s (FDA) most serious safety warning.

In May 2009, the FDA added this warning to the Plavix label. After reviewing more data, the agency said it felt it was important to highlight this risk in a boxed warning.

Plavix is used to prevent blood clots after a recent heart attack or stroke, and in people with certain disorders of the heart or blood vessels. The medication keeps the platelets in the blood from coagulating to prevent unwanted blood clots that can occur with certain heart or blood vessel conditions. There is no way for doctors to measure how well Plavix is working. Generally, if patients avoid another heart attack or stroke, it is thought to be effective.

According to a notice on the FDA Web site, Plavix does not have its anti-platelet effects until it is metabolized into its active form by the liver enzyme, CYP2C19. People who have reduced functioning of their CYP2C19 liver enzyme cannot effectively convert Plavix to its active form. As a result, Plavix may be less effective in altering platelet activity in those people. These “poor metabolizers” may not receive the full benefit of Plavix treatment and may remain at risk for heart attack, stroke, and cardiovascular death.

According to the FDA, it is estimated that 2 percent to 14 percent of the U.S. population are poor metabolizers. The agency recommends that health care professionals consider alternative dosing of Plavix for these patients, or consider using other anti-platelet medications. Tests are available to assess CYP2C19 genotype to determine if a patient is a poor metabolizer.

The FDA is advising patients not to stop taking Plavix unless told to do so by their health care professional. They should talk with their health care professional if they have any concerns about Plavix.

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