Influence of CYP2B6*6 genotype on methadone clearance. Shown are the systemic clearances for IV (A) R-methadone and (B) S-methadone and the apparent oral clearances for oral (C) R-methadone and (D) S-methadone, as box plots (solid line within the box represents the median, dashed line within the box represents the mean, box boundaries are the 25th and 75th percentiles, error bars are the 10th and 90th percentiles, and individual points are outliers). *Significantly different from wild-type (CYP2B6*1/*1), P < 0.05. CL/F = apparent oral clearance.