Cimetidine and ketotifen inhibit stimulated aggregation and histamine liberation from rabbit blood platelets.

The effect of cimetidine and ketotifen was studied on thrombin-stimulated rabbit platelet aggregation as well as on histamine and serotonin liberation. Both drugs inhibited the stimulation of platelets in a dose-dependent way. The effect of ketotifen on stimulated aggregation was about twice that of cimetidine. Stimulated histamine and serotonin liberation was more inhibited by ketotifen than by cimetidine. Both drugs inhibited the liberation of serotonin to a greater extent than that of histamine.