Sanofi-aventis US and Bristol-Myers Squibb Company (BMS) announced revisions to the US prescribing information for Plavix (clopidogrel bisulfate), which include a boxed warning. The boxed warning concerns the diminished effectiveness of Plavix in patients who have a genetic variation leading to reduced formation of the active metabolite. These patients, who are designated as poor metabolizers, represent, according to the prescribing information, approximately 2 per cent of whites, 4 per cent of blacks, and 14 per cent of Chinese. The percentage of poor metabolizers is estimated to be approximately 3 per cent of the population, based on published studies.

Patients should continue taking Plavix unless told to do otherwise by their healthcare professional. They should talk with their healthcare professional if they have any concerns about Plavix.

On March 12, the US Food and Drug Administration (FDA) issued a press release on this update, which is included below:

The US Food and Drug Administration added a boxed warning to the anti-blood clotting drug Plavix (clopidogrel), alerting patients and health care professionals that the drug can be less effective in people who cannot metabolize the drug to convert it to its active form.

Plavix reduces the risk of heart attack, unstable angina, stroke, and cardiovascular death in patients with cardiovascular disease by making platelets less likely to form blood clots. 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.

"We want to highlight this warning to make sure health care professionals use the best information possible to treat their patients," said Mary Ross Southworth, Pharm.D., a clinical analyst in the Division of Cardiovascular and Renal Products in the FDA's Center for Drug Evaluation and Research.

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

It is estimated that 2 per cent to 14 per cent of the US population are poor metabolizers. The FDA 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.

Patients should not 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.

Plavix is made under a Bristol-Myers Squibb - Sanofi Pharmaceuticals partnership.

These revisions to the prescribing information for Plavix reflect the companies’ ongoing research in collaboration with the FDA, which better defines the patient population that may be affected by a genetic variation in CYP2C19 and alternate treatment strategies.

Sanofi-aventis US is an affiliate of sanofi-aventis, a leading global pharmaceutical company that discovers, develops and distributes therapeutic solutions to help improve the lives of patients.

Bristol-Myers Squibb is a global biopharmaceutical company whose mission is to discover, develop and deliver innovative medicines that help patients prevail over serious diseases.