Influence of minor CYP2B6 alleles on the disposition and metabolism of IV and oral methadone. Subjects received 6.0 mg IV methadone HCl and 11.0 mg oral methadone HCl. Shown are plasma concentrations of IV (A) R-methadone and (B) S-methadone and oral (C) R-methadone and (D) S-methadone. Each data point is the mean. Genotype cohorts were CYP2B6*1/*1 (n = 21), CYP2B6*1/*4 (n = 1), CYP2B6*4/*6 (n = 3), and CYP2B6*5/*5 (n = 2).