[Metabolism of lenampicillin hydrochloride. II. Metabolism of promoiety].

The in vitro and in vivo metabolism of promoiety in lenampicillin hydrochloride (LAPC) were investigated in rats and dogs. After incubation of LAPC with intestinal or liver preparations and blood of rat, diacetyl, acetoin and 2,3-butanediol were identified as metabolites of LAPC. The main metabolite in peripheral plasma was 2,3-butanediol after oral administration of LAPC in rats and dogs. On the other hand, high levels of acetoin were found out in portal plasma for early period after dosing of LAPC. These results suggested that the biotransformation of promoiety in LAPC to acetoin carried out mainly in intestinal tissues, but acetoin was converted to 2,3-butanediol in liver. Acetoin and 2,3-butanediol were also excreted in urine, but their urinary excretion were very low, and the combined excretion were accounting for about 9% of dose up to 48 hours after dosing in rats and less than 1% in dogs, respectively. The major metabolic pathways of promoiety in LAPC were postulated as below. (Formula: see text).