Pharmacodynamic and metabolic interactions between ethanol and two industrial solvents (methyl n-butyl ketone and methyl isobutyl ketone) and their principal metabolites in mice.

MnBK and MiBK prolong the duration of ketamine-, pentobarbital-, thiopental- and ethanol-induced loss of righting reflex (LRR) in mice. In equimolar doses, (5 mmol/kg i.p.), both isomers were equipotent with respect to the enhancement of ketamine-, pentobarbital-, and thiopental-induced LRR. However, MnBK was significantly more effective (twice as effective) than its isomer with respect to enhancing ethanol-induced LRR. An attempt to explain the difference in effectiveness between the two isomers was carried out. The effects of both ketones and their principal metabolites, (2-hexanol (2-HOL), 2,5-hexanedione (2,5-HD), 4-methyl-2-pentanol (4-MPOL) and 4-hydroxy 4-methyl-2-pentanone (HMP)) on ethanol-induced LRR and ethanol elimination were studied in mice. The ketones and their metabolites were dissolved in corn oil and injected intraperitoneally 30 min before 4 g/kg ethanol for LRR and 2 g/kg for ethanol elimination. Ethanol-induced LRR was significantly prolonged by the following dosages (mmol/kg), MnBK, 5; MiBK, 5; 2-HOL, 2.5; 4-MPOL, 2.5; and HMP, 2.5; 2,5-HD, 2.5, however exerted no effect. Concentrations of ethanol in blood or brain upon return of the righting reflex were similar in solvent-treated and control animals. The mean elimination rate of ethanol was slower in groups pretreated with MnBK or 2-HOL as compared to control animals. Ethanol elimination in animals pretreated with MiBK, HMP, 4-MPOL, or 2,5-HD was similar to that in control animals. These ketones are known to have some central depressant action on their own. This by itself could lead to prolongation of ethanol-induced LRR. However, MnBK, as well as one of its principal metabolites, (2-HOL), markedly reduced ethanol elimination. This could explain the observation that MnBK has a greater potentiating effect on ethanol-induced LRR that its isomer, MiBK, which does not affect ethanol elimination.