Effect of ampicillin on hepatic microsomal mixed-function oxidase system in male mice.

The effect of ampicillin [(D)-alpha-aminobenzyl penicillin] administration on the hepatic mixed-function oxidase (MFO) system was studied in male mice. Ampicillin (100 mg/kg, i.p., 3 days) decreased the levels of cytochrome P-450, aminopyrine N-demethylase, acetanilide hydroxylase and cytochrome c-reductase activity significantly. In carbon tetrachloride (CCl4)-pretreated mice, ampicillin increased acetanilide hydroxylation compared with CCl4 treatment alone; however, all other parameters of the MFO system remained unchanged. Ampicillin exhibited type II binding with microsomes (trough at 388 nm, peak at 430 nm). Thus ampicillin acts as an inhibitor of the MFO system.