Impact of dabigatran versus phenprocoumon on ADP induced platelet aggregation in patients with atrial fibrillation with or without concomitant clopidogrel therapy (the Dabi-ADP-1 and Dabi-ADP-2 Trials)

Background. A relevant number of patients receive triple therapy with clopidogrel, aspirin, and oral anticoagulation. Clopidogrel's efficacy on ADP induced platelet function may be influenced by concomitant antithrombotic therapies. Data regarding the effect of dabigatran on platelet function is limited to in vitro studies and healthy individuals. Methods. The "Dabi-ADP-1" and "Dabi-ADP-2" trials randomized patients with atrial fibrillation to either dabigatran or phenprocoumon for a 2-week period. In Dabi-ADP-1 (n=70) patients with clopidogrel therapy were excluded and in Dabi-ADP-2 (n=46) patients had to be treated concomitantly with clopidogrel. The primary endpoint was ADP-induced platelet aggregation between dabigatran and phenprocoumon at 14 days. Secondary endpoints were ADPtest HS-, TRAP-, and COL-induced platelet aggregation. Results. There was no significant difference regarding the primary endpoint between both groups in either trial (Dabi-ADP-1: Dabigatran: 846 [650-983] AU × min versus phenprocoumon: 839 [666-1039] AU × min, P=0.90 and Dabi-ADP-2: 326 [268-462] versus 350 [214-535], P=0.70) or regarding the secondary endpoints, ADPtest HS-, TRAP-, and COL-induced platelet aggregation. Conclusion. Dabigatran as compared to phenprocoumon has no impact on ADP-induced platelet aggregation in atrial fibrillation patients neither with nor without concomitant clopidogrel therapy.