Influence of CYP2B6 genotype on the disposition and metabolism of oral methadone. Subjects received 11.0 mg oral methadone HCl (9.9 mg free base). Shown are plasma concentrations of (A) R-methadone, (B) S-methadone, (C) R-EDDP, (D) S-EDDP, and (E) R/S-methadone concentration ratios. Each data point is the mean ± SD. Some SD values are omitted for clarity. Genotype cohorts were CYP2B6*1/*1 (n = 21), CYP2B6*1/*6 (n = 20), CYP2B6*6/*6 (n = 17), and CYP2B6*4/X (n = 4, with results for one CYP2B6*1/*4 and three CYP2B6*4/*6 subjects combined). EDDP = 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine.