Ticagrelor or prasugrel in STEMI patients: a pharmacodynamic evaluation

Background: A recent study has suggested that ticagrelor 90 mg twice daily (bid) provides stronger platelet inhibition than prasugrel 10mg once daily (od) when measured with the VerifyNow P2Y12 assay (VN-P2Y12), in ACS patients. Aim: To compare the effect of ticagrelor 90mg bid and prasugrel 10mg od on platelet reactivity in STEMI patients using different platelet function tests including the VN-P2Y12 Methods: Platelet reactivity was prospectively evaluated using VN-P2Y12 platelet reaction unit (PRU), light transmission aggregometry (LTA) residual platelet agregation (RPA), and Vasodilator-Stimulated-Phosphoprotein (VASP) platelet reactivity index (PRI) 30 days after an acute STEMI. We studied 92 STEMI patients who received either prasugrel 10mg od (n=54) or ticagrelor 90 mg bid (n=38) after primary coronary stenting. Results: On-treatment platelet reactivity evaluated with the VN-P2Y12 assay (PRU) was lower with ticagrelor compared to prasugrel: 20±4.6 vs 55±8.3 (p=0.001). But these results were not confirmed with the other platelet function tests. The more specific test, VASP PRI (%) was 13.6±2.4 on ticagrelor vs. 18.0±2.1 on prasugrel (p=0.18); the more global test, LTA showed a mean RPA (%) of 12.9±2.0 vs. 9.0±1.7 for ticagrelor and prasugrel, respectively (p=0.15) (Figure). High on-treatment platelet reactivity rates were 2.6% with VASP (defined as PRI>50%) and 0% with VN-P2Y12 (PRU>235) and LTA (% RPA > 46.2%) on ticagrelor, while it was 0% with VASP, 1.8% with VN-P2Y12 and LTA on prasugrel. Pharmacodynamic Evaluation Conclusions: VASP and LTA measurements do not confirm the pharmacological superiority of ticagrelor over prasugrel when measured with VN-P2Y12 in STEMI Patients. These results suggest that VN-P2Y12 assay could overestimate the platelet inhibitory effect of ticagrelor.