INTRODUCTION: As ticagrelor, clopidogrel and cangrelor therapies may be used in the same clinical setting, their potential pharmacodynamic interactions are of interest. Hence, we investigated possible interactions between these agents in dogs using a variety of switching protocols. METHODS: Six male dogs all received 7 different dosing regimens separated by 1-5week washout periods: cangrelor (1µg/kg/min, intravenous infusion); ticagrelor (0.8mg/kg, oral); clopidogrel (3mg/kg, intravenous injection); cangrelor together with ticagrelor initiated 10minutes after cangrelor infusion start or clopidogrel given 30minutes after cangrelor infusion start; ticagrelor followed by clopidogrel given 3 or 7hours after ticagrelor dosing. ADP-induced whole blood platelet aggregation was measured by impedance aggregometry. RESULTS: Mean maximum inhibition of platelet aggregation (IPA) was 81-87% at 6minutes (cangrelor), 3hours (ticagrelor) and 4hours (clopidogrel) postdosing and platelet function recovered after 1.5hours, 12hours, and 9days, respectively. IPA at 2hours post clopidogrel was reduced to 39% when clopidogrel was given during cangrelor infusion versus 69% for clopidogrel alone. With clopidogrel dosed 3hours after ticagrelor, IPA was reduced after washout of ticagrelor to 38% at 24hrs vs. 68% for clopidogrel alone, but an interaction was not seen when clopidogrel was dosed 7hours after ticagrelor. No pharmacodynamic interaction occurred between ticagrelor and cangrelor. CONCLUSIONS: The extent of the pharmacodynamic drug-drug interactions observed between clopidogrel and cangrelor or ticagrelor apparently depends on the level of receptor occupancy when clopidogrel is administered. Importantly, no significant pharmacodynamic interaction occurred between ticagrelor/clopidogrel when clopidogrel was given at clinical trough IPA levels with ticagrelor. No significant pharmacodynamic interaction occurred with cangrelor and ticagrelor.