June 29, 2010

On June 28 the American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) issued a clinical alert to physicians regarding the new FDA warning about patient response to the anti-platelet drug clopidogrel (Plavix).

The FDA requires a new warning on the box of clopidogrel products stating that, based on genetic make-up, some patients can’t metabolize the drug into its active form and won’t respond to the drug. The FDA estimates that between 2 percent and 4 percent of patients won’t be able to metabolize the drug. But there is not yet enough information available for developing recommendations on genetic testing of patients, the ACCF and AHA stated in their report.

“What do you do with that FDA warning?” asked Rita Redberg M.D., a professor of medicine in the cardiology division at the University of California San Francisco.

“The specific impact of genetic differences on clinical outcome is really not known. Genetics is not at a point where we can make clinical recommendations based on genetics,” Redberg said.

There are also questions about how genetic testing should be used and if the cost of that would be reimbursed.

Redberg said doctors were really confused by the FDA warning and were wondering if they should be ordering these genetic tests. But they can be expensive and take a while to process and they don’t all fall under FDA supervision, she said.

“It’s very unclear how reliable that information is and what you do with that information once you get it,” Redberg said.

Some alternative drugs seem to have less dependence on genetic factors, but they may cause more bleeding and cost more, the report states. One alternative was recently found to have a significantly higher rate of solid tumors.

Redberg feels the ACCF/AHA report helped ease doctors’ confusion by essentially recommending that they keep doing what they are currently doing.

Some of the recommendations the ACCF/AHA report does make are that genetic testing might be done if a patient is at moderate or high risk of a poor outcome. And in patients who have been taking clopidogrel as prescribed, yet had problems due to the drug not working or working too well and causing bleeding, the report states that might warrant genetic testing, switching to another drug or adjusting the clopidogrel dose.