Effect of etomidate on hepatic drug metabolism in humans

The authors studied the effect of etomidate on drug metabolism in vivo in humans and in vitro using human liver microsomes. When these liver microsomes were incubated with different concentrations of etomidate, dose-dependent inhibition of ketamine N-demethylation, a cytochrome P-450-dependent enzymatic process, was produced. Cytochrome P-450 binding spectra displayed type II binding with a UV light absorption maximum (lambda max) at a wavelength of 424 nm in the presence of etomidate. In vivo studies were conducted using ketamine and antipyrine as substrates. Evaluation of antipyrine's pharmacokinetic variables after an intravenous infusion of etomidate (0.34 +/- 0.17 mg/kg) revealed an 18% increase in its elimination half-life (P = 0.04). In addition, there were 16% and 11% decreases in the area under the curve (P = 0.05) and in the clearance rate (P = 0.07) for antipyrine, respectively. In patients administered a bolus dose of ketamine during brief outpatient operations, etomidate produced no significant changes in ketamine's pharmacokinetics compared to thiopental. The authors conclude that the etomidate-induced inhibition of hepatic drug metabolism can prolong the elimination of drugs with low hepatic clearance rates (e.g., antipyrine). However, etomidate would not be expected to alter the rate of elimination of high clearance anesthetics and analgesic drugs (e.g., ketamine, fentanyl).