THE DURATION OF ACTION OF BUPIVACAINE, PRILOCAINE AND LIGNOCAINE

SUMMARY The duration of analgesia and of hypoaesthesia produced by a variety of solutions has been examined by skin weal testing; each separate study was carried out in twenty female volunteers under double-blind conditions. First, bupivacaine, lignocaine and prilocaine were compared with and without 1 in 200,000 adrenaline. Bupivacaine was found to give significantly longer analgesia than prilocaine and significantly longer hypoaesthesia than both the other agents. Adrenaline significantly lengthened the action of all three drugs, this prolongation being greatest with lignocaine. The second part of the trial compared the duration of action of hospital-prepared and commercially prepared solutions of the three local analgesics plus adrenaline. The commercial ampoule preparations provided significantly longer action than the corresponding drugs in hospital-prepared multidose vials. The third group of experiments studied the effect of doubling the concentrations of the solutions; there was no great increase in duration of analgesia but the duration of hypoaesthesia was lengthened, significantly so with bupivacaine. Throughout all the above studies the individual results with bupivacaine showed a greater range of variation than those with the other agents. Finally the analgesic effect of saline (with and without adrenaline) was investigated; it was found that both agents generally produced a similar brief period of hypoaesthesia. The findings and their practical implications are discussed.