Influence of premedication with diazepam or morphine on the induction dose of eltanolone

Background: This study examined the influence of premedication with morphine or diazepam on the dose of eltanolone, a steroidal intravenous anaesthetic agent, required to induce anaesthesia. Methods: Two hundred and sixteen patients, aged 18 to 65 years, were randomly assigned to receive premedication with diazepam 10 mg orally, morphine 10 mg intramuscularly, or placebo. The double-dummy technique was used to maintain blinding. Eltanolone 0.16-0.75 mg · kg^-1 was given intravenously over 20 s. At the commencement of injection patients were instructed to begin counting; if the patient ceased counting within 120 s and failed to respond to commands to continue, anaesthesia was considered to have been induced. The dose required to anaesthetise 50% of patients (ED₅₀) was determined by logistic regression. Results: The ED₅₀ (95% confidence interval) of eltanolone in patients who received placebo premedication was 0.31 (0.27-0.34) mg · kg^-1. It was reduced slightly and nonsignificantly by premedication with diazepam, to 0.27 (0.24-0.30) mg · kg^-1, or morphine, to 0.26 (0.23-0.29) mg · kg^-1. Involuntary movement occurred in 65% of placebo premedicated patients. Its incidence was not significantly reduced by diazepam (57%), but was significantly (P<0.001) reduced by morphine (37%). Morphine premedication was, however, associated with a significant (P<0.01) increase in the incidence of apnoea (21%) compared to placebo premedicated patients (4%). Conclusion: Premedication with diazepam or morphine had little influence on the dose of eltanolone required to induce anaesthesia.