Infusion strategies to investigate the pharmacokinetics and pharmacodynamics of hypnotic drugs: etomidate as an example.

Etomidate was administered to six healthy volunteers by microprocessor controlled infusions, to generate three cycles of linearly increasing plasma levels, with an anticipated slope of 0.05 microgram ml-1 min-1. The infusions were stopped when a deep hypnotic state was obtained, as indicated by burst suppressions in the EEG. The infusions were restarted when the volunteers were fully orientated to person, place and time. The mean (+/-SD) doses of etomidate delivered by the first, second and third infusion were 165 +/- 30, 137 +/- 25 and 157 +/- 26 mg, respectively. Certain clinical signs were observed and related to the plasma concentrations of etomidate. Pharmacokinetic analysis was undertaken using an open two-compartment model. The therapeutic window was in a range of plasma concentrations between 0.3 and 1.0 microgram ml-1 of etomidate. Pharmacokinetic analysis gave a volume for the central compartment of 50 +/- 11 litre, an apparent volume of distribution of 252 +/- 51 litre and a total clearance of 1693 +/- 504 ml min-1. Microprocessor controlled infusions can serve as a powerful tool for research in clinical pharmacology. The achievement of linearly increasing plasma levels of etomidate allowed further pharmacokinetic and pharmacodynamic modelling concepts to be realized.