FDA Adds Boxed Warning to Plavix Label to Highlight Reduced Effectiveness of the Drug In Poor Metabolizers

The U.S. Food and Drug Administration (FDA) has updated the label information for the commonly used anti-clotting medication Plavix® (clopidogrel) to stress to physicians that patients carrying certain genetic variations may not receive the full benefit from the drug.

Plavix reduces the chance a harmful clot will develop by preventing blood cells called platelets from sticking together. Usually prescribed in combination with aspirin, Plavix has been shown to help reduce the risk of subsequent heart attacks or strokes in people who have already suffered from a cardiovascular event. Plavix also reduces the risk of heart attack and stroke in people diagnosed with peripheral artery disease.  The drug is also is used to lower the risk of blood clots in people with unstable angina (chest pain) caused by partially blocked arteries and in those who have had a stent implanted to help keep their arteries open.

Once inside the body, Plavix is absorbed in the intestines and then converted into its active form by enzymes in the liver. But some people have genetic variations that reduce the activity of one of the most critical enzymes — CYP2C19. This, in turn, reduces the amount of active drug in the bloodstream and its effectiveness in preventing clots.

The FDA first added information about poor metabolizers of Plavix to the drug label in May 2009. Additional data has prompted them to add the boxed warning to further caution physicians that some of their patients may be at risk, inform them that testing for CYP2C19 variations is available (although no test is FDA-approved specifically for determining Plavix efficacy), and recommend that other medications or increased dosages of Plavix be used in patients identified as poor metabolizers.

“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 a press release.

A recently approved drug, Effient® (prasugrel), may be an alternative for some patients identified as poor metabolizers. Like Plavix, Effient prevents platelets from forming blood clots. The advantage is that the conversion of Effient to its active form can take place in the presence of the genetic variations that affect Plavix. Studies have shown that Effient is effective at preventing heart attacks, strokes and stent-blocking clots.  The risk of dangerous bleeding, however, is higher with this drug.

23andMe Health Edition and Complete Edition customers can view their data for genetic variations in CYP2C19 in the Clopidogrel (Plavix) Efficacy Drug Response Report.

A downloadable PDF version of the Clopidogrel (Plavix) Efficacy report is available to help customers share their results with their doctors.

Only a physician can determine whether Plavix is the right medication for a particular patient and at what dosage it should be given.  The information contained in 23andMe Drug Response reports should not be used to independently establish a drug regimen or abolish or adjust an existing course of treatment.  If you are concerned about Plavix, talk to a health professional.

  • Read more about the Plavix label update here and here.
  • Just last month the FDA updated the label on another anti-clotting medication, warfarin, to include more information on the effects of genetic variations.  Read more here in the Spittoon.