Effects of isoniazid on hepatic drug oxidation and N-acetylation capacities in rats.
In vitro and in vivo activity of hepatic monooxygenase as well as in vivo N-acetylation capacity were assessed in male Wistar rats after oral pretreatment with 10 and 50 mg/kg isoniazid for 7 d. Both doses of isoniazid showed no statistical difference in protein contents, total cytochrome P-450 and the activities of aminopyrine N-demethylase as well as ethoxyresorufin-O-deethylase in the 9000 x g liver homogenate suspension compared to the saline pretreated group. Body and relative liver weights remained also unchanged. In vivo isoniazid pretreatment with either dose hardly changed the kinetic profiles and parameters of phenazone and sulfadimidine (free + total). The results suggest that drug metabolizing pathways that can be evaluated by the metabolism of the model substances employed here may not be modified by prolonged isoniazid treatment.