Effect of quinidine on platelets.

The effects of quinidine on platelets over a wide range of concentrations of the drug were studied. It was found that quinidine at high concentrations (1 and 1.5 mM) induced platelets to undergo profound ultrastructural changes and 14C-serotonin release. In addition, the drug at these concentrations caused marked inhibition of platelet aggregation mediated by adenosine diphosphate, adrenaline, collagen and arachidonate but had no effect on ristocetin-induced agglutination. However, quinidine at 10 microM (a pharmacological concentration) had only a variable inhibitory effect on adrenaline-induced platelet aggregation.