ETOMIDATE

ETOMIDATE

" / would have everie man write what he knowes and no more."—MONTAIGNE BRITISH JOURNAL OF ANAESTHESIA VOLUME 48, No. 3 MARCH 1976 ETOMIDATE The co...

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" / would have everie man write what he knowes and no more."—MONTAIGNE

BRITISH JOURNAL OF ANAESTHESIA VOLUME 48, No. 3

MARCH 1976

ETOMIDATE

The continuing search for the perfect i.v. anaesthetic agent has yielded etomidate, a carboxylated imidazole molecule prepared as an aqueous solution and neutralized with phosphate buffer. The first report of the drug by Janssen and others (1971) showed that it caused a rapid onset of sleep in rats and that cardiovascular side effects were less common than when a similar depth and duration of hypnosis was obtained with thiopentone. Etomidate is a product of Janssen Laboratories and has been in use in a few centres on the continent of Europe since 1972 (Doenicke et al., 1973) and is currently on limited availability for clinical trials in the United Kingdom. The dose required for the induction of anaesthesia is approximately 0.3 mg/kg body weight. In this issue, there are three further reports on etomidate. Dr Holdcroft and others (p. 199) confirm earlier reports that involuntary muscular movements are an unacceptable side-effect of this agent, although, as in the case of methohexitone, Althesin and propanidid, the incidence of movements may be reduced by premedication with narcotics or other sedative drugs such as diazepam. Other excitatory side effects, such as cough and hiccup are less troublesome, but may occur in about 10% of those receiving etomidate. Dr Kay describes similar results from the use of etomidate in children (p. 207). Pain associated with the injection of etomidate, particularly into small veins on the dorsum of the hand, is an important disadvantage. The problem may be reduced by injection to larger veins, or by the addition of lignocaine to the solution, although Kay has found that the latter remedy is not always successful. On the credit side, cardiovascular stability appears to be a feature of etomidate and, in the dose required to induce anaesthesia, respiratory depression is not a

problem. Doenicke and others (1973), in a study in human volunteers, found that the injection of etomidate did not increase the plasma histamine concentration, while the reports of clinical studies have commented on the absence of allergic reactions. Many will regard this as encouraging, although most anaesthetists will have learned to accept such claims with guarded optimism at such an early stage in the history of a drug. It is customary to claim that new intravenous anaesthetic agents are metabolized rapidly. However, understandable cynicism may be tempered by Dr Kay's second paper (p. 213) showing an apparent absence of cumulation as judged on clinical grounds in man. Thus, etomidate may be worthy of trial as a continual intravenous infusion anaesthetic in the situation for which Savege and others (1975) have used Althesin infusions in the hope of improving on the unacceptably long recovery times which these authors experienced (17.9 min + 0.95). It may be stated now that etomidate is not the "ideal anaesthetic". However, at a time when some anaesthetists are exploring methods which lessen the need for gaseous anaesthetics, it merits further study. REFERENCES

DoenickejA., Lorenz, W., Beigh, R., Bezecny,H., Uhlig, G., Kalinar, L., Praetorius, B., and Mann, G. (1973). Histamine release after intravenous application of shortacting hypnotics. Br.J. Anaesth., 45, 1097. Janssen, P. A. J., Niemegeers, C. J. E., Schellekens K. H. L., and Lenaerts, F. M. (1971). Etomidate (R-( + )-l(a methyl-benzyl)imidazole-5-carboxylate) (R 16659)—a potent short-acting and relatively atoxic intravenous hypnotic agent in rats. Arzneim Forsch., 21, 1234. Savege, T. M., Ramsay, M. A. E., Curran, J. P., Cotter, J., Walling, P. T., and Simpson, B. R. (1975). Intravenous anaesthesia by infusion. Anaesthesia, 30, 757.

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