Intravenous diazepam and oral ethanol interaction.

The mechanism of the interaction between ethanol and diazepam is not known. Six healthy male subjects (aged 21 to 32 yr) were randomly assigned in a balanced crossover study to each of two treatments, 28 days apart: (1) diazepam 10 mg intravenously over 20 min, preceded by 60 min with ethanol 0.7 gm/kg (diluted to 20% v/v) orally over 15 min and followed for 8 hr by ethanol 0.15 gm/kg/hr to maintain the blood alcohol concentrations between 800 to 1,000 mg/l; (2) diazepam 10 mg intravenously over 20 min. The area under the curve (AUC) for total diazepam increased in all subjects (30.1 +/- 10.7%, mean = SD, p < 0.02) after ethanol. Since AUCfree diazepam also rose in all (mean - 26.5 +/- 17.3%) and AUC of the metabolite N-desmethyldiazepam fell (mean = 50.5 +/- 11.7%, p < 0.01) there had been inhibition of hepatic intrinsic clearance of free drug. The susceptibility of individuals to inhibition of N-desmethylation by ethanol is qualitatively determined by total drug concentrations. Estimation of free diazepam concentration coupled with measurement of metabolite affords a qualitative and quantitative evaluation of the mechanism of this interaction.