Impact of liver fibrosis and clinical characteristics on dose-adjusted serum methadone concentrations.

ABSTRACT

BACKGROUND: There is limited knowledge on the causes of large variations in serum methadone concentrations and dose requirements. OBJECTIVES: We investigated the impact of the degree of liver fibrosis on dose-adjusted steady-state serum methadone concentrations. METHODS: We assessed the clinical and laboratory data of 155 Norwegian patients with opioid use disorder undergoing methadone maintenance treatment in outpatient clinics in the period 2016-2020. A possible association between the degree of liver fibrosis and dose-adjusted serum methadone concentration was explored using a linear mixed-model analysis. RESULTS: When adjusted for age, gender, body mass index, and genotypes of CYP2B6 and CYP3A5, the concentration-to-dose ratio of methadone did not increase among the participants with liver fibrosis (Coefficient 0.70; 95% CI -2.16, 3.57; P 0.631), even among those with advanced cirrhosis (-0.50; -4.59, 3.59; 0.810). CONCLUSIONS: Although no correlation was found between the degree of liver stiffness and dose-adjusted serum methadone concentration, close clinical monitoring should be considered, especially among patients with advanced cirrhosis. Still, serum methadone measurements can be considered a supplement to clinical assessments, taking into account intra-individual variations.