The Influence of Three Phenothiazine Derivatives and of Amiphenazole on the Action of Methadone: Studies with Two Algesimetric Methods in Untrained Human Subjects

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Abstract
The influence of the phenothiazine derivatives chlorpromazine, acepromazine and mepazine and of the phenylthiazole derivative amiphenazole on the pain-threshold-raising action of methadone is described. The tests were made in untrained human subjects by two algesimetric methods, one involving thermal stimulation of the skin, and the other mechanical stimulation of the finger nail-bed. The thermal method was reliable, whereas the mechanical one did not disclose analgesic potency. Chlorpromazine and acepromazine, proved to have analgesic activity but did not significantly increase the analgesic effect of methadone. Mepazine, which lacked analgesic activity, antagonised the methadone analgesia. Amiphenazole was found to exert an analgesic action by itself but it did not decrease the potency of methadone. The side-effects of methadone were increased by chlorpromazine and acepromazine, but were uninfluenced by mepazine and amiphenazole.