Abstract 4948: Decrease in Poor Responders on Switching From Clopidogrel to Prasugrel: Results From the SWitching Anti Platelet (SWAP) Study
Background: The SWAP study, a prospective double-blind study in patients with a recent history of acute coronary syndrome (ACS), demonstrated that switching from a stable maintenance dose (MD) of clopidogrel (Clop) 75 mg/day to prasugrel (Pras) 10 mg/day, with or without a 60 mg loading dose (LD), resulted in significantly lower platelet aggregation by one week. This analysis reports on a secondary objective of the SWAP study evaluating the effect of switching from Clop to Pras on thienopyridine poor response rates.
Methods: Poor response to Pras and Clop was evaluated in 100 patients (Placebo LD/Clop 75mg/day, n=33; Placebo LD/Pras 10mg/day, n=36; Pras 60 mg LD/Pras 10mg/day, n=31). Poor responders were defined as patients with maximum platelet aggregation (MPA) >65% to 20 μM ADP assessed by light transmittance aggregometry performed prior to randomization and at 2 hr, 24 hrs, and 7 days following start of study drug.
Results: Prior to randomization, the Clop poor response rate was 27%. Poor responder rates in each group at 2 hrs, 24 hrs, and 7 days post study drug initiation are shown in the Figure⇓. At 2 hrs and 24 hrs, there were no poor responders in patients receiving a LD of Pras. At the end of the 7-day MD period, the poor responder rate in the combined Pras groups (with and without LD) was significantly lower compared with Clop (5% vs. 21%; p=0.014).
Conclusions: In patients with recent ACS, switching from Clop to Pras MD is associated with reduced poor response rates (or frequency of high platelet reactivity), while Pras LD overcomes any poor response seen with Clop.