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.
