Badhan RKS, et al. - For the management of opioid dependency during pregnancy, methadone use is commonplace. Researchers herein sought for the most appropriate optimal dosing regimens during pregnancy. A pharmacokinetic modeling approach was applied in this study to determine gestational changes in R- and S-methadone concentrations in maternal plasma and fetal (cord) blood and, in turn, to identify a theoretical optimal dosing regimen during pregnancy, and the influence of Cytochromes P450 (CYP) 2B6 and 2C19 polymorphisms on methadone maternal and fetal pharmacokinetics. Per findings, levels of methadone plasma reduce during gestation. They suggest necessity for methadone dose escalation throughout gestation. Minimization of fetal exposure is emphasized to avert neonatal abstinence syndrome. Mothers may require dose of up to 180 mg daily in trimester 3.