Alterations in methadone metabolism during late pregnancy

J Addict Dis. 1999;18(4):51-61. doi: 10.1300/J069v18n04_05.


Traditionally, methadone maintenance therapy has been a once-daily dosing schedule. The current study evaluates the effectiveness of this regimen during pregnancy. A total of 23 pregnant and 16 non-pregnant opioid-dependent patients were studied in two phases to evaluate pregnancy-dependent changes in methadone pharmacokinetics. In the first phase, pregnant patients had a statistically significant higher elimination rate constant (k) and lower half-life compared to non-pregnant controls. In the second phase, the apparent clearance (Cl/F) was significantly greater during pregnancy, with preliminary data suggesting that this observation results from a decrease in the fraction of dose absorbed (F). The implications of these findings on dosing regimens during pregnancy is discussed.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Dose-Response Relationship, Drug
  • Drug Administration Schedule
  • Female
  • Half-Life
  • Humans
  • Methadone / administration & dosage
  • Methadone / pharmacokinetics*
  • Methadone / therapeutic use
  • Narcotics / administration & dosage
  • Narcotics / pharmacokinetics*
  • Narcotics / therapeutic use
  • Opioid-Related Disorders / rehabilitation*
  • Pregnancy
  • Pregnancy Complications / rehabilitation*
  • Pregnancy Trimester, Third / physiology


  • Narcotics
  • Methadone