All mice (male, 8-week-old) were treated with corn oil or 10 mg/kg/day RIF (po) for three days. Livers were collected 24 h after the last dose and microsomes were prepared. PIs metabolic stability was determined according to their metabolic rates by monitoring parent drug disappearance. APV, NFV, SQV and MDZ were detected by LC-MS/MS. Metabolic stability of APV (A), SQV (B), and NFV (C) was expressed as % of control (n=3). The metabolic stability in the control group was set at 100% for each chemical and each mouse line. Metabolic stability of MDZ (D) was used as positive control for these experiments. *p < 0.05 compared with the corresponding control.