[The effect of etomidate on the activity of human pseudocholinesterase. In vivo-in vitro-enzymekinetics (author's transl)].

Etomidate (Hypnomidate), a safe and effective short-acting hypnotic drug of special value for induction of anesthesia, seems to be a noncompetitive activator, as well as a competitive inhibitor, of pseudocholinesterase E.C. 3.1.1.8). This is analogous to the effects of morphine and its derivatives with which etomidate has a structural similarity. The analysis of enzyme kinetics in vitro gave a Km of 10.4 (+/- 1.1) microM and a Vmax of 2.4 (+/- 0.3) mmoles/1 min for the hydrolysis of S-butyrylthiocholine by human pseudocholinesterase. Etomidate does not show any influence on the reaction rate of pseudocholinesterase on S-butyrylthiocholine in the standard test. From the experimental results it is derived that even under in vivo conditions of induction of anesthesia by etomidate, no influence is to be expected on the turnover of succinylcholine by the normal pseudocholinesterase. There is no explanation for the occasionally prolonged postnarcotic apnea following administration of etomidate as far as competition of etomidate with succinylcholine for the pseudocholinesterase is concerned and as long as enzyme variants of higher affinity for etomidate can be excluded.