Abstract
Summary
The effects of histamine and a large number of antihistaminic drugs upon the coagulation of normal and heparinized rabbit plasma have been investigated. It has been established that the amount of each compound required for an antiheparin effect is critical. At concentrations below the critical level the drugs have little or no effect upon the coagulation system studied. At concentrations above this level several of the antihistaminics as well as histamine produced a progressively increased incoagulability of the system. This anticoagulant effect is related to concentration and the action is on some substance other than heparin. Thenfadil, methapyrilene and thonzylamine had no effect upon normal or heparinized plasma. Of all the compounds tested, 194-B, methaphenilene, pyranisamine, 204, phenazoline, tripelennamine, diphenhydramine, pyrathiazine, P.D. AH-853 and p-Fluorobenzyl D.P.E. gave the best results in that, upon reaching the critical concentration for heparin inactivation, they did not become anticoagulants themselves. It has been postulated that the antiheparin activity of these compounds is due to their direct combination with heparin.
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