title: Altered methadone pharmacokinetics in pregnancy: implications for dosing.
abstract: Lower plasma methadone levels have been reported in pregnant women receiving methadone maintenance for heroin addiction. Methadone pharmacokinetics was examined in a 24-year-old woman 8 months pregnant with twins, who experienced severe withdrawal symptoms beginning 10-12 hours after her daily 30 mg methadone dose. Methadone plasma concentration-time data were fit to a one-compartment pharmacokinetic model by extended least-squares regression. Estimated half-life for methadone was 8.1 hours, which is much shorter than the usual methadone half-life (greater than 24 hours). Plasma methadone concentrations were estimated for the cases of a) increasing the 30 mg methadone dose by 50% and administering it once daily and b) continuing the 30 mg methadone dose but administering it at 12-hour intervals. Although the model is derived from a single subject, the simulations performed clearly suggest a need for altered methadone dosing in pregnancy. More sustained plasma methadone levels are achieved with twice-daily dosing of methadone than are achieved by administering an increased methadone dose once daily. Twice-daily dosing would be expected to produce fewer withdrawal symptoms and, ultimately, improved compliance with treatment.
authors.affiliation: Department of Psychiatry and Human Behavior, Brown University Program in Medicine, Providence, Rhode Island.
authors.forename: R M
authors.initials: RM
authors.lastname: Swift
authors.forename: M
authors.initials: M
authors.lastname: Dudley
authors.forename: P
authors.initials: P
authors.lastname: DePetrillo
authors.forename: P
authors.initials: P
authors.lastname: Camara
authors.forename: W
authors.initials: W
authors.lastname: Griffiths
mesh_terms: D000328:Adult; D003198:Computer Simulation; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D006207:Half-Life; D006556:Heroin Dependence / Q000097:blood* / Q000534:rehabilitation; D006801:Humans; D007231:Infant, Newborn; D008657:Metabolic Clearance Rate / Q000502:physiology; D008691:Methadone / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000097:blood* / Q000534:rehabilitation; D011272:Pregnancy, Multiple / Q000502:physiology
chemical_list: D008691:Methadone