Majority of Patients Taking Blood-Thinners Given Wrong Dose

A new study suggests that approximately 75% of patients taking two common blood-thinning drugs may be receiving the wrong dosage levels.

Researchers at the Intermountain Medical Center Heart Institute (Murray, UT, USA) conducted a study involving 521 patients receiving P2Y12 inhibitor therapy with either clopidogrel or prasugrel. To ascertain if the patients were receiving the correct dosage of their prescribed medication, they conducted a blood-clotting test using the VerifyNow platelet function assay, as measured by P2Y12 reaction units (PRU). Guidelines for the use of platelet-function testing target a PRU of 100-200 and recommend changing medication dosing or type to reach this target.

The researcher found that based on PRU assays, 50% of the patients taking clopidogrel were getting too little of the drug to prevent clotting most effectively while 25% were getting too much; only 25% were getting an accurate dose. Regarding prasugrel, 50% were getting too much of the drug, which could lead to dangerous bleeding while 25% were getting too little; again, only 25% were getting the appropriate dose. The researchers also found that none of the baseline clinical variables of age, sex, hypertension, hyperlipidemia, heart failure, renal failure, prior cardiac history, or other nonplatelet related medications is predictive of PRU results. The study was presented at the American Heart Association (AHA) Scientific Sessions, held during November 2012 in Los Angeles (CA, USA).

“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,” said lead author and study presenter cardiologist Brent Muhlestein, MD. “There's a sweet spot, an appropriate range for each patient. But we found that not many people are falling into that range.”

The VerifyNow System, a product of Accumetrics (San Diego, CA, USA) measures platelet reactivity by the rate and extent of light changes in whole blood as platelets aggregate over time, in response to agonists that are specific to various antiplatelet medications. Within the test device wells, the instrument measures the increase in light transmittance over time. A patient’s blood sample that exhibits inhibited platelet function produces low light transmittance, whereas a sample with normal platelet function produces high light transmittance. The system is based on the principles of optical aggregometry.

Related Links:
Intermountain Medical Center Heart Institute
Accumetrics