The therapeutic potential of centrally acting dopamine agonists

Abstract

Much interest has been stimulated by epidemiological evidence which suggests that abortion, foetal abnormality, haemo- poietic disorders and neuropathy occur- ring in operating theatre staff might be due to chronic exposure to waste anaes- thetic gases. The interaction of nitrous oxide and vitamin B~2 can explain each of these disorders. In contrast, there is no theoretical or experimental basis for believing that they could be caused by exposure to trace concentrations of halothane or other currently used volatile anaesthetic agents. The lowest level at which nitrous oxide has been shown to cause signifi- cant inhibition of methionine synthase is 1 000 p.p.m. 9 which is also the lowest concentration at which foetotoxicity has been observed in rodents. 450 p.p.m, is the highest concentration demonstrated to be without effect on hepatic meth- ionine synthase activity in rats dur- ing prolonged exposure 9. Comparable measurements cannot easily be made in man but the data from rats suggest that the maximum safe concentration lies between 450 p.p.m, and 1 000 p.p.m. and allowance for a two-fold safety mar- gin would then suggest that prolonged exposure to 200 p.p.m, should be safe. Levels in excess of 200 p.p.m, com- monly occur in unscavenged operating theatres and the interaction of nitrous oxide and vitamin Bl2 pro~4des an unanswerable case for scavenging waste gases in any area in which aaaesthetics are administered. Levels of 25 p.p.m. can certainly be attained with the use of a cuffed tracheal tube and an efficient scavenging system.