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Doctors have been left to figure out if Plavixwill work in their patients and how best to protect them if it doesn’t. The confusion follows this month’s FDA warning that Plavix may not work well in certain patients.
Plavix is used to prevent blood clots after a recent heart attack or stroke, and in people with certain disorders of the heart or blood vessels. It is also given to patients who’ve undergone coronary stent procedures to prevent clots from forming inside the devices. The medication keeps the platelets in the blood from coagulating to prevent unwanted blood clots that can occur with certain heart or blood vessel conditions.
On March 12, the FDA warned that Plavix may be less effective in people who cannot metabolize the drug to convert it to its active form. According to a notice on the FDA Web site, 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. These “poor metabolizers” may not receive the full benefit of Plavix treatment and may remain at risk for heart attack, stroke, and cardiovascular death.
In May 2009, the FDA added this warning to the Plavix label. In its latest alert, the agency said that after reviewing more data, it felt it was important to highlight this risk in a Black Box, its strongest safety notice.
According to a report in today’s Wall Street Journal, as many as 4 percent of patients have two copies of a variation in a gene for CYP2C19 that makes them poor metabolizers. For patients of Chinese decent, the rate could be as high as 14 percent. The new Black Box warning is directed at such patients.
But according to the Journal, of concern is another group of patients, 25 to 30 percent, who have one copy of this variation. At least one study suggests that these patients may also have a degree of inhibition to the drug’s effectiveness.
To insure that Plavix is working doctors have a couple of options. One is a genetic test to determine if a patient carries this gene variation. Patients who test for the variant could be put on a higher dose of Plavix. Unfortunately, insurance won’t always cover this test, and according to the Journal, some doctors point out that whether using the tests will actually decrease risk for patients hasn’t been well studied.
Another option is switching to a drug called Effient, which was recently approved and which isn’t affected by the genetic variant. According to the Journal, doctors have been slow to use Effient because it does carry a higher risk of bleeding than Plavix.
In the meantime, doctors are advising against patients going off Plavix without first talking to their own physicians.