Variability Of Platelet Inhibition As Determined By The Verifynow Assay Among Patients Receiving Clopidogrel Or Prasugrel: Results From A Real World Registry

Background: Dual oral antiplatelet therapy with aspirin and some form of P2Y 12 inhibition is critical for the prevention of future CV events among many pts with CAD. A variety of studies using the VerifyNow™ platelet function assay (as measured by P2Y 12 reaction units [PRU]) have documented significant variability in the levels of P2Y 12 inhibition provided by either clopidogrel or prasugrel and that this variability may be associated with an increased incidence of either ischemic events or bleeding. However, the significance and frequency of such variability in a real world setting is not well known. Methods: The Intermountain Healthcare Department of Cardiovascular Medicine has developed guidelines for the use of platelet function testing among pts requiring dual antiplatelet therapy. These guidelines target a PRU of 100-200 and recommend changing medication dosing or type to reach target. Here, we report the results of the initial VerifyNow™ assay performed on 521 patients receiving P2Y 12 inhibitor therapy with either clopidogrel or prasugrel. Results: Average age was 68±13 yrs, 66% of pts were male and 87% received drug-eluting stents. Mean (median) PRU levels for those receiving clopidogrel (n=381) and prasugrel (n=140) were 211.5±103.2 (219) and 107.6±92.1 (80) respectively. Of patients receiving clopidogrel, 66(17.3%), 97(25.5%) and 218(57.2%), and of those receiving prasugrel, 78(55.7%), 32(22.9%) and 30(21.4%) had PRU 200 respectively. Therefore, only 24.8% of all pts were initially found to be within target range. Interestingly, none of the baseline clinical variables of age, sex, hypertension, hyperlipidemia, heart failure, renal failure, prior cardiac history or other non-platelet related medications were predictive of PRU results. Conclusions: Among pts receiving initial dual antiplatelet therapy and platelet function testing in real world setting, less than a quarter have a PRU within the target range. Pts receiving clopidogrel tend to be under-inhibited, and prasugrel, over-inhibited. Although long-term outcomes remain to be identified, these initial findings demonstrate a large potential for individual targeted dosing of antiplatelet therapy for pts receiving either clopidogrel or prasugrel.