Update in Anaesthesia Pentazocine Karen Henderson Correspondence Email:
[email protected] Introduction use with 30 - 40 mg of pentazocine equivalent In 1967 pentazocine became the first opioid to 10 mg morphine. When given by mouth, the agonist-antagonist to be introduced into analgesic action of pentazocine is much weaker clinical practice as an analgesic. It was hoped than morphine and is thought to lie somewhere that pentazocine would prove to be a powerful between that of peripherally acting analgesics analgesic, free of the side-effects of opioid such as paracetamol and weak opioids such as narcotics, particularly avoiding drug dependency. codeine. In practice pentazocine has proved to be less Other actions of pentazocine mirror those of effective than hoped, but it is still used widely in other opioids including respiratory depression, Clinical Overview Articles resource-poor countries. cough suppression, miosis, decreased gastric Chemistry emptying and constipation and increased smooth Pentazocine is a benzmorphan which is muscle tone in the uterus and bladder. However chemically related to morphine. It is a white or in normal use these effects are usually of little cream, odourless, crystalline powder. It consists clinical significance. of a racemic mixture of dextro- (d) and laevo- In contrast to other strong opioid analgesics Summary (l) isomers which is soluble in acidic aqueous however, there is a dose-related systemic This article describes solutions. Pentazocine hydrochloride is used for and pulmonary hypertension, increased left the pharmacology oral use and the lactate form is used for parenteral ventricular end-diastolic pressure and a rise in and rectal administration. and clinical uses of central venous pressure, probably as a result of the opioid agonist- Molecular weight (free base)........................321.9 a rise in plasma catecholamine concentrations.