(Undated) -- In the future, the popular anti-clotting drug Plavix will carry a new warning about "reduced effectiveness" in some patients. The Food and Drug Administration announced the decision to add the new warning on Friday, saying some users may have a poor response to the drug if they are unable to break it down to its active form. The FDA estimates the number of so-called "poor metabolizers of Plavix" to be anywhere from two to 14-percent of the population. Mary Ross Southworth with the administration's Center for Drug Evaluation and Research says because those poor metabolizers make "less of the active form there is less anti-platelet effect in the blood and the patient may not receive the full benefit of Plavix treatment." Plavix is an eight-billion-dollar-a-year drug sold by Bristol-Myers Squibb and Sanofi Aventis.
