Interaction between ethanol and flunitrazepam in rats: Pharmacokinetic mechanisms and toxicological implications

Flunitrazepam (FNZ) is frequently co-used with ethanol, yet the pharmacokinetic mechanisms underlying their interaction remain poorly understood. To elucidate potential pharmacokinetic interactions between these two agents, male Sprague-Dawley rats were administered 1 or 3 mg/kg of FNZ with or without 30%(v/v) ethanol (8.4 mL/kg, p.o.), and plasma concentrations of FNZ and its two major metabolites, N-desmethylflunitrazepam and 3-hydroxyflunitrazepam, were quantified using a validated LC-MS/MS method. Co-administration with ethanol resulted in significantly increased C_max and AUC values for both FNZ and its metabolites across both FNZ dose levels. Metabolite-to-parent ratios and in vitro metabolic profiling indicated that the enhanced systemic exposure was primarily attributable to increased absorption, rather than inhibition of hepatic metabolism. These findings support an absorption-mediated pharmacokinetic mechanism through which ethanol may potentiate FNZ exposure, with potential implications for the toxicological assessment of benzodiazepine-ethanol co-use.