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Cited by 599Pharmacogenetics and Drug MetabolismOpioid Use Disorder TreatmentPain Management and Opioid Use

Interindividual Variability of the Clinical Pharmacokinetics of Methadone: Implications for the Treatment of Opioid Dependence

Eap, Chin B., Buclin, Thierry, Baumann, Pierre·2002·Clinical Pharmacokinetics
DOI 10.2165/00003088-200241140-00003
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Abstract

Methadone is widely used for the treatment of opioid dependence. Although in most countries the drug is administered as a racemic mixture of (R)- and (S)- methadone, (R)-methadone accounts for most, if not all, of the opioid effects. Methadone can be detected in the blood 15-45 minutes after oral administration, with peak plasma concentration at 2.5-4 hours. Methadone has a mean bioavailability of around 75% (range 36-100%). Methadone is highly bound to plasma proteins, in particular to alpha(1)-acid glycoprotein. Its mean free fraction is around 13%, with a 4-fold interindividual variation. Its volume of distribution is about 4 L/kg (range 2-13 L/kg). The elimination of methadone is mediated by biotransformation, followed by renal and faecal excretion. Total body clearance is about 0.095 L/min, with wide interindividual variation (range 0.02-2 L/min). Plasma concentrations of methadone decrease in a biexponential manner, with a mean value of around 22 hours (range 5-130 hours) for elimination half-life. For the active (R)-enantiomer, mean values of around 40 hours have been determined. Cytochrome P450 (CYP) 3A4 and to a lesser extent 2D6 are probably the main isoforms involved in methadone metabolism. Rifampicin (rifampin), phenobarbital, phenytoin, carbamazepine, nevirapine, and efavirenz decrease methadone blood concentrations, probably by induction of CYP3A4 activity, which can result in severe withdrawal symptoms. Inhibitors of CYP3A4, such as fluconazole, and of CYP2D6, such as paroxetine, increase methadone blood concentrations. There is an up to 17-fold interindividual variation of methadone blood concentration for a given dosage, and interindividual variability of CYP enzymes accounts for a large part of this variation. Since methadone probably also displays large interindividual variability in its pharmacodynamics, methadone treatment must be individually adapted to each patient. Because of the high morbidity and mortality associated with opioid dependence, it is of major importance that methadone is used at an effective dosage in maintenance treatment: at least 60 mg/day, but typically 80-100 mg/day. Recent studies also show that a subset of patients might benefit from methadone dosages larger than 100 mg/day, many of them because of high clearance. In clinical management, medical evaluation of objective signs and subjective symptoms is sufficient for dosage titration in most patients. However, therapeutic drug monitoring can be useful in particular situations. In the case of non-response trough plasma concentrations of 400 microg/L for (R,S)-methadone or 250 microg/L for (R)-methadone might be used as target values.

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  • Elimination half-lives of opioids can relate to both genetic and nongenetic factors, and this can influence withdrawal effects.

    “Additionally, the elimination half-lives of opioids can relate to both genetic (e.g. variations in CYP P450 iso-enzymes) and nongenetic factors (such as other interactions with other medications or substances), 50 and this can influence withdrawal effects.”

    From Tapering and withdrawing opioids: guidance informed by fundamental principles to minimise withdrawal symptoms (2025) · cites this paper as [50]

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Authors
Eap, C. B., Buclin, T., & Baumann, P.
Affiliations
  • Hôpital de Cery (CH)
  • Centre Hospitalier Universitaire Vaudois (CH)
Corresponding author
Eap, Chin B.
ORCID
Venue
Clinical Pharmacokinetics
Publisher
Springer Science and Business Media LLC
Published
2002
Volume
41
Issue
14
Pages
1153-1193
ISSN
0312-5963 (ISSN-L)
DOI
10.2165/00003088-200241140-00003
OpenAlex
W1979097034
Cited by
599
References
227
Citations by year
2026: 24 · 2025: 16 · 2024: 13 · 2023: 17 · 2022: 18 · 2021: 33 · 2020: 26 · 2019: 24 · 2018: 26 · 2017: 21 · 2016: 26 · 2015: 30 · 2014: 30 · 2013: 39 · 2012: 38
FWCI
2.18
Type
journal article
Language
en
Open access
closed
Locations
  • Clinical Pharmacokinetics (publishedVersion)
  • PubMed (publishedVersion)
  • IRIS (submittedVersion)
  • SERVAL (Université de Lausanne) (submittedVersion)
Topics
  • Life Sciences › Pharmacology, Toxicology and Pharmaceutics › Pharmacology › Pharmacogenetics and Drug Metabolism
  • Health Sciences › Medicine › Public Health, Environmental and Occupational Health › Opioid Use Disorder Treatment
  • Health Sciences › Medicine › Anesthesiology and Pain Medicine › Pain Management and Opioid Use
Keywords
methadone, interindividual variability, opioid use disorder, opioid maintenance treatment, CYP3A4, CYP2D6, drug interactions, enzyme induction, enzyme inhibition, alpha-1-acid glycoprotein, plasma protein binding, elimination half-life, bioavailability, volume of distribution, drug clearance
MeSH terms
Cytochrome P-450 Enzyme System, Dose-Response Relationship, Drug, Humans, Injections, Intravenous, Methadone, Opioid-Related Disorders, Narcotics, Stereoisomerism, Drug Monitoring

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