CPIC Finds Insufficient Evidence to Change Methadone Dosing Based on CYP2B6 Genotype
This CPIC guideline systematically reviewed CYP2B6 genetic variation in the context of methadone therapy for opioid use disorder and pain. Despite clear pharmacokinetic effects on S-methadone levels, the consortium concluded that current evidence does not support genotype-based dose adjustments for clinical outcomes or QTc prolongation. The guideline is important for laboratories considering CYP2B6 panel inclusion, as it defines a well-characterised gene-drug pair where actionability has not yet been established.
The original study
Clinical Pharmacogenetics Implementation Consortium Guideline for CYP2B6 Genotype and Methadone Therapy.
- Authors
- Robinson KM, Eum S, Desta Z, Tyndale RF, Gaedigk A, Crist RC, et al.
- Journal
- Clinical pharmacology and therapeutics
- Type
- Journal Article, Practice Guideline, Systematic Review
- PMID
- 38863207
Original abstract
Methadone is a mu (μ) opioid receptor agonist used clinically in adults and children to manage opioid use disorder, neonatal abstinence syndrome, and acute and chronic pain. It is typically marketed as a racemic mixture of R- and S-enantiomers. R-methadone has 30-to 50-fold higher analgesic potency than S-methadone, and S-methadone has a greater adverse effect (prolongation) on the cardiac QTc interval. Methadone undergoes stereoselective metabolism. CYP2B6 is the primary enzyme responsible for catalyzing the metabolism of both enantiomers to the inactive metabolites, S- and R-2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (S- and R-EDDP). Genetic variation in the CYP2B6 gene has been investigated in the context of implications for methadone pharmacokinetics, dose, and clinical outcomes. Most CYP2B6 variants result in diminished or loss of CYP2B6 enzyme activity, which can lead to higher plasma methadone concentrations (affecting S- more than R-methadone). However, the data do not consistently indicate that CYP2B6-based metabolic variability has a clinically significant effect on methadone dose, efficacy, or QTc prolongation. Expert analysis of the published literature does not support a change from standard methadone prescribing based on CYP2B6 genotype (updates at www.cpicpgx.org).