November 14, 2012
Study: 75% of Clopidogrel/Prasugrel Users on
Wrong Dose

Salt Lake City—Most patients taking clopidogrel and prasugrel may have inadvertently been prescribed the wrong dose.

That’s according to cardiology researchers at the Intermountain Medical Center Heart Institute, who found that approximately 75% of patients taking the two common blood-thinning drugs may be receiving the wrong dosage levels.

Their study was presented recently at the American Heart Association Scientific Sessions 2012 in Los Angeles.

Current guidelines recommend that all patients take the same standardized dose of clopidogrel (Plavix) and prasugrel (Effient), according to the report, but, using the VerifyNow platelet function assay, researchers found that the recommended dose is not effective for all patients.

“There's a sweet spot, an appropriate range for each patient. But we found that not many people are falling into that range,” said cardiologist Brent Muhlestein, MD, a cardiac researcher at the Intermountain Medical Center Heart Institute. “We showed that by performing a simple blood test to see whether or not the blood is clotting properly, we can determine whether patients are getting an appropriate, individualized dose of the medications. The test is easy to perform, but not widely used.”

The study found that, among 521 patients receiving initial dual antiplatelet therapy and platelet function testing in a real world setting, less than a quarter had P2Y12 reaction units (PRU) within the target range. Patients receiving clopidogrel tended to be under-inhibited, according to the researchers, while those on prasugrel were over-inhibited.

Common indicators such as age, gender, cholesterol levels, and history of heart problems were not good predictors of how patients would react to the drugs, according to the researchers who called for a more individualized approach.

“Although long-term outcomes remain to be identified, these initial findings demonstrate a large potential for individual targeted dosing of antiplatelet therapy for patients receiving either clopidogrel or prasugrel,” the authors write.

“That means there's not an easy way to predict how a person will react to these drugs. But the blood test is very effective,” Muhlestein said. “In fact, a physician could have the test machine on his or her desk and perform the test right there in the office."

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