Hypnotic Effects of an Antihistamine—methapyrilene Hydrochloride

IT is widely recognized that one of the important side effects of the anti-histamines as a class is their sedative action; it has also been considered the most characteristic.1 Controlled studies of their hypnotic (sleep-inducing) effect, however, are lacking. This side effect may be either desirable or objectionable, depending on the situation in which the drug is employed. It was obvious that such a side effect might be used to good advantage as a primary action, i.e., the use of antihistamines as hypnotics. This would seem to be of some value, since the toxicity of this class of compounds is low. Despite the fact that adequate evidence of their value as hypnotics is not available, the antihistamines have been used widely for this purpose. Indeed, some antihistamines, e.g., methapyrilene hydrochloride, are adver-tised extensively to the public and sold in large quantities for their hypnotic effect since, unlike other hypnotics such as the barbiturates, they may be dispensed without prescription. Inasmuch as the sedative effects of dif-ferent members of this large class of compounds are extremely variable,2 it seemed desirable to perform a controlled study of one of the compounds which is advertised and used for its hypnotic effect. Methapyrilene hydro-chloride (Histadyl, Dormin, Thenylene Hydrochloride) was selected for this purpose. In a study of this compound, by Feinberg and Bernstein,8 sedation was a common finding, occurring in 48 (or 19%) of 253 patients, most of whom received 50 mg. doses. The degree of sedation was not so great as that produced by Benadryl, but approximated or perhaps exceeded that ex-perienced with Pyribenzamine. Friedlaender and Friedlaender4 noted drowsiness in 13 of 117 patients with 100 mg. doses. Kierland and Potter 5 reported that 10 of 126 patients experienced drowsiness with this drug on doses of 100 mg. three to four times daily. Most authors have reported minimal and infrequent toxic effects with methapyrilene. These have con-sisted of vertigo, nervousness, dryness of the mouth and throat, excitation, insomnia, headache, nausea and diarrhea.