Effect of chronic ketanserin treatment on serotonin-induced platelet aggregation in patients with Raynaud's phenomenon.

To investigate whether the variable efficacy in Raynaud's phenomenon of long-term oral ketanserin treatment might be related to variation in the sensitivity of 5-HT2 receptors to ketanserin, serotonin-induced platelet aggregation was measured in ten patients with Raynaud's phenomenon at various times after treatment with ketanserin. Platelet aggregation was completely inhibited 90 min after 40 mg ketanserin, but not 12-14 h after the last dose of 40 mg on the 31st day of continuous twice daily administration. However, 90 min after an additional dose of 40 mg, platelet aggregation was again completely inhibited. The present results indicate that ketanserin 40 mg b.d. does not continuously inhibit platelet 5-HT2 receptors in patients with Raynaud's phenomenon and suggest that more frequent intake might be more effective.