Ethanol drug interaction with chlordiazepoxide and pentobarbital.

Drug interactions between ethanol and pentobarbital and ethanol and chlordiazepoxide were investigated utilizing mice. At the peak of oral ethanol (0-4 g/kg), either sodium pentobarbital (1-120 mg/kg) or chlordiazepoxide hydrochloride (2-400 mg/kg) was given intraperitoneally. Blood concentrations of ethanol, pentobarbital, chlordiazepoxide, and its pharmacologically active major metabolites were monitored utilizing either gas chromatography or high performance liquid chromatography. Lethality and loss-of-righting reflex were measured as indexes of behavioral drug interactions. It was evident from the isobolographic plot that the interactions between ethanol and pentobarbital and ethanol and chlordiazepoxide were more than additive. Interaction between ethanol and pentobarbital was greater than that between ethanol and chlordiazepoxide. Furthermore, with increasing ethanol pretreatment the shift in dose-response curves for the loss-of-righting reflex was affected more than the shift in dose-response curves for lethality. Blood concentration monitoring of each drug indicated that the rate of biotransformation of pentobarbital was significantly decreased; sequential biotransformation of chlordiazepoxide was also altered, resulting in a large accumulation of demethylchlordiazepoxide in the blood.