Pharmacokinetics of methadone

Area of Science:

• Pharmacology
• Clinical Pharmacy

Background:

• Methadone is a synthetic opioid used for pain management and opioid dependence treatment.
• Its pharmacokinetic profile differs significantly from morphine, featuring higher bioavailability and a longer half-life.
• Hepatic metabolism by cytochrome P450 enzymes contributes to methadone's variable pharmacokinetics.

Purpose of the Study:

• To review and summarize the literature on methadone's pharmacokinetics.
• To highlight factors influencing methadone's therapeutic effects and potential toxicities.
• To provide guidance on optimizing methadone therapy, including in special populations.

Main Methods:

• Literature search of AMEDLINE database from 1966 to May 2005.
• Review and synthesis of publications relevant to methadone disposition (absorption, distribution, metabolism, excretion).
• Discussion of general dosing guidelines, opioid conversions, and pharmacokinetic considerations in specific patient groups.

Main Results:

• Methadone exhibits variable pharmacokinetics impacting analgesia onset, magnitude, and duration.
• Drug interactions are common and necessitate close patient monitoring.
• Special populations (pediatric, renal failure, elderly, pregnant) may require dosage adjustments.

Conclusions:

• Optimizing methadone therapy requires understanding its pharmacokinetics, pharmacodynamics, and patient-specific factors.
• Clinicians must consider individual patient characteristics for effective and safe methadone prescribing.
• Comprehensive knowledge of methadone disposition is crucial for managing pain and opioid dependence.