The Food and Drug Administration said Friday that it will require a new black-box warning on the label of the popular anti-clotting drug Plavix to indicate that some patients do not metabolize the drug properly and may receive little benefit from it. The warning indicates that the drug is dangerous only in the sense that it doesn't work in those patients and thus may leave them unprotected against heart attacks and strokes.
Plavix, known generically as clopidogrel, is one of the most popular drugs in the world, with U.S. sales of $3.8 billion in 2008 and worldwide sales of $6.6 billion in 2009, according to IMS Health. It is used to prevent clotting of blood in patients who have stents or other prostheses or conditions that predispose them to clotting, and thus strokes and heart attacks. Technically, clopidogrel is a pro-drug that must be converted into its active form in the body by enzymes in the liver, particularly one called CYP2C19. As much as 14% of the population have an inactive or a less-active form of this enzyme, so the active form is not produced or produced only in limited quantities in the body. Very limited studies have hinted that giving higher doses of clopidogrel might yield higher blood levels of the active form, but the FDA cautioned that no clinical trial has verified this.
There is a genetic test to identify patients with the aberrant form of the enzyme, and the agency recommends that physicians order the test if there are any doubts about using the drug. There are also other alternatives that may be prescribed instead of Plavix, including aspirin. Patients should not stop taking Plavix unless told to do so by their physicians, the FDA said.
The new warning appears on the label of the drug in a black box — hence the name — which is considered the most severe form of warning.
— Thomas H. Maugh II