Alterations in response to somatic pain associated with anaesthesia. V. The effect of promethazine.

ALTHOUGH it has never been claimed that the phenothiazines have an analgesic action comparable to that of the opiates, it is frequently inferred that they have some effect on pain. They are widely used to potentiate analgesic drugs in the management of intractable pain and have enjoyed great popularity in the treatment of the terminal stages of malignant disease. Apart from their anti-emetic effect, the rationale of the pre-operative use of the phenothiazines has never been clearly defined. Here they are usually administered in combination with analgesics and their sedative and tranquillizing properties are considered to be highly desirable. This popularity is evidenced by the marketing of the 'Tamergan" preparations which contain pethidine and promethazine. When these first became available the authors were evaluating a method of analgesimetry, using pethidine 100 mg as the standard drug. It was expected thatPamergan P.100 (pethidine 100 mg and promethazine 50 mg) would produce a more marked and consistent degree of analgesia than pethidine alone. As will be shown later, this was not the case and this surprising finding led us to study the effects of promethazine 50 mg and the above mentioned mixture in more detail.