Potentiation of ifosfamide toxicity by chlordiazepoxide, diazepam and oxazepam.

The effects of chlordiazepoxide, diazepam and oxazepam on the lethal toxicity and metabolic activation of ifosfamide were investigated in mice. Ifosfamide was administered 24 h after the final injection of chlordiazepoxide, diazepam or oxazepam (100 mg/kg/d for 3 d, i.p.). The prior administration of chlordiazepoxide, diazepam or oxazepam enhanced the toxicity of ifosfamide (778 mg/kg, i.p.) during observation for 6 d after the administration of ifosfamide. In chlordiazepoxide-, diazepam- or oxazepam-treated mice, a higher concentration of active metabolite in the plasma after the administration of ifosfamide (200 or 600 mg/kg, i.p.) was observed as compared with that in mice treated with ifosfamide alone. On the other hand, chlordizepoxide, diazepam or oxazepam markedly enhanced the activity of ifosfamide oxidase in the liver microsomes. These results suggest that the potentiation of ifosfamide toxicity is due to stimulation of the metabolic activation of ifosfamide by chlordizepoxide, diazepam and oxazepam.