The Food and Drug Administration added a boxed warning to blood thinner drug Plavix on Friday, alerting patients and health care professionals to the drug's potential for reduced effectiveness in people who cannot metabolize the drug to convert it to its active form.
Plavix is co-marketed by Bristol-Myers Squibb (BMY) and Sanofi-Aventis (SNY). The drug reduces the risk of heart attack, unstable angina, stroke, and cardiovascular death in patients with cardiovascular disease by preventing the blood from forming platelets, which clump together to form clots.
Plavix has its anti-platelet effects only when it is metabolized into its active form by the liver enzyme, CYP2C19. Therefore, people who have reduced functioning of their CYP2C19 liver enzyme will not be able to convert Plavix to its active form, which results in reduced effectiveness, the FDA said.
It is estimated that 2% to 14% of the U.S. population are poor metabolizers and there are tests to assess CYP2C19 genotype to determine if a patient is a poor metabolizer.
In a statement the FDA said "These poor metabolizers may not receive the full benefit of Plavix treatment and may remain at risk for heart attack, stroke, and cardiovascular death and therefore, health care professionals should consider alternative dosing of Plavix for these patients, or consider using other anti-platelet medications".
The warning about Plavix' potential for reduced effectiveness in poor metabolizers was added to the drug's label in May 2009. The regulatory agency after reviewing more data is now highlighting the risk in a boxed warning.
Last November, the FDA warned that the anti-clotting effect of Plavix may be reduced by about half if the drug is taken along with heartburn drugs like Prilosec and Nexium.
Plavix is marketed overseas as Iscover. The drug is scheduled to lose patent protection in the U.S. in 2012. In 2009, global sales of Plavix/Iscover totaled $9.3 billion.
SNY closed Friday's trading at $38.04, down 0.39% on a volume of 1.36 million shares. BMY closed the day's trade at $25.89, down 0.27% on a volume of 11.79 million shares.
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