The effect of CYP2B6*6 variant allele on the selected PK parameters of BUP in mid- and late pregnancy: OHBUP/BUP metabolic ratio (M.R.) (A), AUCss of OHBUP (B) and AUCss of BUP (C). M.R., defined as the ratio of AUCs, corrected for mol. wt.; mid-pregnancy, 22–26 weeks of gestation; late pregnancy, 34–38 weeks of gestation.