[Isoniazid and rifampicin in the rabbit. Effect on hepatic microsomal enzyme activity]

1. Enzymatic induction or inhibition induced by isoniazid (10 mg/kg) and/or rifampicin (13 mg/kg) oral treatment of 13 days in the rabbit, is evaluated with the following parameters: --variation of antipyrine half-life measured before treatment and 24 h after the end of treatment, --cytochrome P450 content, aniline hydroxylase and aminopyrine N-demethylase activities in hepatic microsomes. Isoniazid half-life is evaluated before treatment, in order to obtain an homogeneous repartition of animals in each group: isoniazid, rifampicin, isoniazid + rifampicin and control. 2. Rifampicin treatment gives a variable enzyme induction of antipyrine metabolism, cytochrome P450 and aniline hydroxylase activity; aminopyrine N-demethylase activity is significantly inhibited. Isoniazid treatment inhibits antipyrine metabolism and increases the cytochrome P450 content.