Effect of verapamil on platelet aggregation

The influence of the calcium channel blocker verapamil on the aggregation of human blood platelets was studied in vitro in comparison with the calcium channel blocker diltiazem and with the 5-HT antagonist cyproheptadine. Verapamil inhibited the 5-HT-potentiated. ADP-induced aggregation more effectively than the aggregation induced by adrenaline, ADP and collagen. Verapamil antagonized the 5-HT effect in a noncompetitive manner. The same was true of cyprohepatadine which was by more than one order of magnitude more potent than verapamil in inhibiting the 5-HT-induced aggregation. Diltiazem was much less effective than verapamil.