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Reduced effectiveness of Plavix (clopidogrel) in patients who are poor metabolizers of the drug


The U.S. Food and Drug Administration (FDA), the counterpart for Saudi Food and Drug Authority (SFDA), has added a Boxed Warning to the label for Plavix, the anti-blood clotting medication. The Boxed Warning is about patients who do not effectively metabolize the drug (i.e. "poor metabolizers") and therefore may not receive the full benefits of the drug.

Plavix is given to reduce the risk of heart attack, unstable angina, stroke, and cardiovascular death in patients with cardiovascular disease. Plavix works by decreasing the activity of platelets, making platelets less likely to form blood clots.

For Plavix to work, enzymes in the liver (particularly CYP2C19) must convert (metabolize) the drug to its active form. Patients who are poor metabolizers of the drug, do not effectively convert Plavix to its active form. In these patients, Plavix has less effect on platelets, and therefore less ability to prevent heart attack, stroke, and cardiovascular death. It is estimated that 2 to 14% of the population are poor metabolizers; the rate varies based on racial background.

FDA recommends that healthcare professionals should:

  • Be aware that some patients may be poor metabolizers of Plavix. They do not effectively convert Plavix to its active form because of low CYP 2C19 activity.The effectiveness of Plavix as a preventive therapy is reduced in these patients.
  • Be aware that tests are available to determine patients' CYP2C19 status.
  • Consider use of other anti-platelet medications or alternative dosing strategies for Plavix in patients who have been identified as poor metabolizers.
  • Be aware that although a higher dose regimen (600 mg loading dose followed by 150 mg once daily) in poor metabolizers increases antiplatelet response, an appropriate dose regimen for poor metabolizers has not been established in a clinical outcome trial.

Patients currently taking Plavix should:

  • Be aware that some patients do not convert Plavix to its active form as well as other patients. These patients may not get the same benefit from Plavix and are known as poor metabolizers.
  • Not stop taking Plavix unless told to do so by their healthcare professional.
  • Talk with their healthcare professional if they have any concerns about Plavix.
  • Talk with their healthcare professional to see if testing to determine their metabolizer status is appropriate.


Report Adverse Drug Reactions to the Saudi FDA

The SFDA urges both healthcare professionals and patients to report side effects from the use of medications to the SFDA either online, by regular mail or by fax, using the following contact information:

National Pharmacovigilance Center (NPC)

Saudi Food and Drug Authority-Drug sector

3292 Northern Ring Road

Al Nafal District

Riyadh 13312 – 6288

Kingdom of Saudi Arabia

Tel: 012759222 ext. 2334, 2352, 2353, 2354, 2356

Fax: 012107398

Email :