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FRIDAY, March 12 (HealthDay News) -- The anti-clotting drug Plavix must now carry a "black box" warning on its label, alerting patients and doctors that some people don't metabolize the medication properly, U.S. health officials said Friday.
Patients with a certain genetic variation can't convert the blood thinner into its active form, which puts them at risk for heart attack and stroke, the U.S. Food and Drug Administration warned.
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"If the patient makes less of the active form, there is less antiplatelet effect in the blood, and the patient may not receive the full benefit of Plavix treatment," Mary Ross Southworth, FDA's deputy director for safety in the division of cardiovascular and renal products at the Center for Drug Evaluation and Research, said during an afternoon press conference.
These patients are called poor metabolizers, she said.
Clopidogrel (Plavix) is generally prescribed after a heart attack, stroke or a procedure to open blocked coronary arteries. It usually makes platelets less likely to form blood clots, thus reducing the risk of heart attack, unstable angina, stroke and cardiovascular death in patients with cardiovascular disease.
For the drug to do its work, liver enzymes, especially one called CYP2C19, must convert the drug to its active form. In patients with low levels of the enzyme, the drug may be less effective in preventing heart attack, stroke and cardiovascular death, according to the FDA.
About 2 percent to 14 percent of people fall into this category, with the percentages varying by race. About 2 percent of whites have the variation, while 4 percent of blacks and 14 percent of Chinese people do, Southworth said.
But patients should not stop taking Plavix without consulting their doctor, the FDA said, noting a test to assess the CYP2C19 genotype can determine if a patient is a poor metabolizer.
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