TABLE 3

Comparison of EC₅₀ values for concentration-dependent induction of CYP2B6 and CYP3A4 activities by prototypical inducers Rates of bupropion hydroxylation and testosterone 6β-hydroxylation were determined with microsomes isolated from human hepatocyte preparations treated daily for 3 days with 0.4 to 40 μM CLZ, 10 μM to 2 mM PB, 0.4 to 400 μM PHN, and 0.1 to 150 μM RIF. The relationship between enzyme activity and inducer concentration was fit with the Hill equation by nonlinear regression to recover estimates for the EC₅₀ and sigmoidicity factor (γ). The EC₅₀ values represent the mean ± S.D. from three individual livers (HL-N140, HL-N145, and HL-N147 for RIF and PB, and HL-N140, HL-N145, and HL-N148 for PHN and CLZ). Statistical significance of the differences in the EC₅₀ values for CYP2B6 and CYP3A4 induction was determined using a two-tailed paired t test.