The effects of ethanol ingestion and repeated benzene exposures on benzene pharmacokinetics

Two groups of C57Bl/6J mice were exposed to 300-ppm benzene vapor, 6 hr/day, 5 days/week for 20 exposures. One group received 10% ethanol (EtOH) in the drinking water commencing 20 hr prior to the initial exposure and continuing 5 days/week throughout the study. The second group received tap water. The uptake and clearance of benzene was followed in the blood during and after the 1st and 20th exposures. During the first benzene exposures, the mean steady state benzene concentrations in benzene/EtOH-treated mice and benzene/water-treated mice were 5.2 and 10.7 micrograms/ml, respectively. The mean elimination rate constants for the benzene/EtOH- and benzene/water-treated groups were 0.124 and 0.042 min-1, respectively. By 20 exposures, the benzene/EtOH group showed no change in mean blood steady state concentration (Css); however, the Css of the benzene/water group was reduced to 7.9 micrograms/ml. The mean elimination rate constants for the two groups were not different after the 20th exposure. The benzene/water mice exhibited a shift from mono-to biexponential clearance between the 1st and 20th exposures. Monoexponential clearances were observed for the benzene/EtOH group at both time points. These results indicate that 1 day of 10% EtOH consumption causes dramatic effects on benzene kinetics. After 20 days of treatment, the benzene/water and benzene/EtOH animals are kinetically similar. These changes in kinetics can be explained by the ability of ethanol and benzene to alter benzene metabolism.