High-dose aspirin in dogs increases vascular resistance with limited additional anti-platelet effect when combined with potent P2Y12 inhibition

Introduction: With the arrival of the potent P2Y(12) antagonists, ticagrelor and prasugrel, the need for co-treatment with aspirin in acute coronary syndromes must be re-examined. This study assessed whether high-dose aspirin: a) provides additional anti-platelet efficacy, assessed in vivo and ex vivo, when combined with P2Y(12) inhibition; and/or b) has a negative effect on vascular function. Materials and Methods: Using an anaesthetized dog model of thrombosis, the effects of aspirin (50 mg/kg) in addition to clopidogrel and ticagrelor were evaluated at two levels of P2Y(12) inhibition, maximal (>= 96%) and sub-maximal (similar to 80%), as assessed by ex vivo ADP-induced whole blood impedence aggregometry. Results: In the absence of aspirin, maximal and sub-maximal P2Y(12) inhibition inhibited arachidonic acid-induced platelet aggregation by approximately 80% and 24%, respectively, without affecting platelet TXA(2) formation. During maximal P2Y(12) inhibition, aspirin provided less additional inhibition of ex vivo arachidonic acid-and collagen-induced platelet aggregation, as compared with sub-maximal P2Y(12) inhibition, without additional anti-thrombotic effect in vivo. Aspirin significantly decreased in vivo PGI(2) production (27%) and increased vascular resistance (16%), independently of P2Y(12) antagonism. Conclusion: In the dog, P2Y(12) antagonists inhibit TXA(2)-mediated platelet-aggregation independently of aspirin. Aspirin provides less additional anti-platelet effects during maximal compared with sub-maximal P2Y(12) inhibition but increases vascular resistance. (C) 2013 Elsevier Ltd. All rights reserved.