Reduced sensitivity of human platelets to PAF-acether following ticlopidine intake

We investigated in 9 patients the effect of a 7-day treatment by Ticlopidine (250 mg b.i.d.) on washed platelets activation by PAF-acether in comparison with adenosine 5'-diphosphate (ADP) and arachidonic acid (AA). Aggregations induced by ADP were totally suppressed upon drug administration. AA-induced aggregations were partly but significantly inhibited (p less than 0.05). Responses of platelets to PAF-acether before treatment differed from patient to patient. A paired Student's test and a two-way analysis of variance showed a significant inhibitory effect of Ticlopidine treatment on PAF-acether-induced aggregation. The inhibitory effect of Ticlopidine or its metabolite(s) was evidenced after platelet washing procedure, suggesting a persistent effect of this drug on platelet after administration of the drug has been stopped.