METHAPYRILENE hydrochloride (thenylpyramine hydrochloride; N,N-dimethyl-N'[2-thenyl] - N'-[2 -pyridyl] - ethylenediamine hydrochloride; histadyl®) is a derivative of ethylenediamine, which recently has been widely used by allergists for its antihistamine properties. During the past two years many reports have been published in the general medical literature dealing with its effectiveness in treatment of experimental and clinical hypersensitivities.
Landau and Gay1 made a comparative study of antihistamine compounds, utilizing the Dale experiments. In these experiments the in vitro histamine neutralizing effects of nine common antihistamine compounds were tested. Methapyrilene hydrochloride was found to be one of the most potent of the histamine-competing agents. In later experiments these authors2 tested the same nine compounds for their activity in vivo against histamine intoxication and anaphylactic shock in guinea pigs. They again found methapyrilene hydrochloride to be one of the most effective agents in protecting against histamine intoxication and anaphylactic shock. Subsequently, clinical reports have appeared