Ticlopidine Activity on Platelet Function in Patients with Enhanced Platelet Aggregation

In a single-blind crossover study, the effect of ticlopidine (250 mg t.i.d.) on platelet function was investigated in 16 patients, with enhanced platelet aggregation, before treatment, on the third and seventh day of treatment with the drug or the placebo. Bleeding time was significantly lengthened by ticlopidine administration. Platelet aggregation, both in vivo and in vitro, was significantly inhibited during the week on ticlopidine. Beta-thromboglobulin concentration was on an average significantly decreased. The inhibition by PGI2 of platelet aggregation by PGD2 was slightly but not significantly increased. Platelet TxB2 production after stimulation with thrombin was unchanged during ticlopidine administration, whereas conversion of exogenous arachidonic acid into TxB2 was slightly but significantly reduced. The present results confirm that ticlopidine acts in vivo as a powerful antiaggregating agent. The antiaggregating activity seems to be due to an interference of ticlopidine with platelet membrane and, as a consequence, with various platelet membrane receptors and activities.