[Impact of application time of aspirin and clopidogrel on platelet aggregation in patients with acute coronary syndrome].

Objective: To observe the impact of various application time of aspirin and clopidogrel on the circadian rhythm changes of platelet aggregation in patients with acute coronary syndrome.

Methods: Patients with acute coronary syndrome were divided into day-time (8:00) and night-time (20:00) medication group (n = 15 each). After plasma concentration reached steady state, platelet aggregation was assessed at 5 time points within 24 hours with a mobile four-channel whole blood impedance aggregometer. The platelet aggregation was induced by ADP and arachidonic acid. Thereafter, the two groups were exchanged and platelet aggregation was assessed in the same way post plasma steady state.

Results: Arachidonic acid-induced platelet aggregation was the highest at 10:00 Am [(7.96 +/- 3.64) ohm] and the lowest at 0:00 [(6.12 +/- 3.29) ohm, P > 0.05] in day-time group. Platelet aggregation was the highest at 20:00 [(9.40 +/- 5.39) ohm] and the lowest at 10:00 [(5.46 +/- 3.93) ohm], P < 0.05). ADP-induced platelet aggregation was the highest at 10:00 and the lowest at 16:00 in day-time group (P > 0.05) and was the highest at 20:00 and the lowest at 10:00 in night-time group (P > 0.05). Platelet aggregation induced by two inducers was significantly higher at 10:00 in day-time group compared to values in night-time group (all P < 0.05).

Conclusion: Taking aspirin and clopidogrel at 20:00 was superior to taking the same medications at 8:00 for inhibiting peak platelet aggregation in the morning.