STUDIES ON PAIN. MEASUREMENT OF THE EFFECT OF MORPHINE, CODEINE, AND OTHER OPIATES ON THE PAIN THRESHOLD AND AN ANALYSIS OF THEIR RELATION TO THE PAIN EXPERIENCE

Abstract

The pain threshold raising action of various opium derivatives was ascertained in terms of the normal threshold. Morphine sulphate in quantities of 0.1 mg.-0.30 mg. and codeine phosphate in quantities from 15 mg.-240 mg. were thus assayed. The minimum effective quantity of morphine sulphate was 0.5 mg., and the smallest amt. with which the highest threshold-raising effect was attained was 30 mg.; the highest threshold level attained was 100% above the control level. For codeine phosphate this quantity was 60 mg. and the highest threshold level was 50% above the control threshold. The threshold-raising action of 3 mg. of dihydromorphinone hydrochloride ("Dilaudid") and of 6.6 mg. of methyldihydro-morphinone ("Metopon") was comparable to that obtained with 30 mg. of morphine. 20 mg. of pantopium hydrochloride ("Pantopon") was equivalent to 8 mg. of morphine. The threshold-raising action of opium derivatives, as well as other observable effects, was reduced or obliterated by pain, when the pain stimulus preceded or occurred early in the course of the action of the opiate. This antagonism between pain and the threshold-raising action of opiates was simulated by the adm. of a sympathomimetic agent (epinephrine) before the opiate was administered. In normal subjects, the outstanding psychological effects of morphine were: freedom from anxiety, feelings of contentment and relaxation, apathy, difficulties in mentation, lethargy and sleep. The presence of an opiate accentuates the ability to dissociate pain perception from the pattern of pain reaction. The therapeutic effectiveness of the opiates is dependent mainly on 3 properties: the threshold-raising action; the dissociation of pain perception from the usual reaction to pain; and the induction of lethargy and sleep.