Summary
Antihistamines are frequently given to haemophilic patients prior to replacement therapy. As these compounds have inhibitory properties against platelets, the relative effects of three commonly used antihistamines against platelets were compared. The actions of promethazine, chlorpheniramine, or mepyramine were tested against platelet aggregation induced by A.D.P., collagen, noradrenaline, and 5 hydro-xytryptamine, as well as platelet adhesiveness and the in vivo rat tail bleeding time. Overall, promethazine had the greatest inhibitory effects, mepyramine had intermediate, and chlorpheniramine least effect. It is suggested that these findings may be important when antihistamines are given to patients with intrinsic coagulation defects and that the compounds which possess the greatest inhibitory action against platelets should be avoided.
