According to results of the RAPID (Rapid Activity of Platelet Inhibitor Drugs) trial, the platelet inhibitor prasugrel was found to be non-inferior to ticagrelor in terms of platelet reactivity two hours after a loading dose among patients with ST-Elevation Myocardial Infarction (STEMI).

Results from the clinical trial were published on April 8 in the Journal of the American College of Cardiology. The RAPID trial looked at 50 patients with STEMI undergoing primary percutaneous coronary intervention (PCI) within 12 hours of symptom onset. Patients received bivalirudin and were randomized to receive loading doses of prasugrel (60 mg) or ticagrelor (180 mg). Results showed two hours after loading dose administration, the platelet reactivity units (PRU) were 217 and 275 in the prasugrel and ticagrelor groups, respectively, a non-statistically significant difference that met the prespecified criteria for non-inferiority.

Additional Resources Full Study Journal Scan  2013 ACCF/AHA Guideline for the Management of STEMI

In addition, high residual platelet reactivity, defined as a PRU ≥240, was evident in approximately one-half of patients in both treatment arms at two hours. A minimum of four hours was required with both drugs to achieve effective platelet inhibition. Further, the independent predictors of high residual platelet reactivity at two hours were morphine use (odds ratio: 5.29; 95 percent confidence interval: 1.44 to 19.49; p = 0.012) and baseline PRU value (odds ratio: 1.014; 95 percent confidence interval: 1.00 to 1.03; p = 0.046).

Previous studies have evaluated the pharmacodynamics of these agents in health volunteers and those with stable coronary artery disease, wrote lead investigator Guido Parodi, MD, PhD, Careggi Hospital, Florence, Italy, and colleagues. "The present study provides several unique and important insights in the treatment of STEMI patients by primary PCI," he added. "As expected, baseline PRU value resulted as a predictor of high residual platelet reactivity two hours after drug loading dose. Thus, higher is the activation of the platelet in STEMI patients before treatment and more time the new antiplatelet drugs take to achieve a sufficient platelet inhibition … however, if these finding will be confirmed by further studies, more caution should be used regarding morphine administration in STEMI patients," they conclude.

Keywords: Odds Ratio, Coronary Artery Disease, Myocardial Infarction, Platelet Aggregation Inhibitors, Thiophenes, Piperazines, Blood Platelets, Confidence Intervals, Morphine, United States, Percutaneous Coronary Intervention

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