Liver damage indices as a tool for modifying methadone maintenance treatment: a cross-sectional study.

Aim: To assess the effect of liver damage on methadone metabolism in opiate addicts undergoing methadone maintenance treatment (MMT).

Methods: This cross-sectional study recruited 74 patients treated at the outpatient clinic of Public Health Institute of Split-Dalmatia County from 2013-2016. Concentrations of methadone and its main inactive metabolite were measured in participants' biological samples on regular check-ups. Urine samples obtained before oral methadone intake, and blood and urine samples obtained 90 minutes after methadone intake were analyzed using gas chromatography/mass spectrometry. Participants were divided into groups according to liver damage criteria: hepatitis C virus status (positive, negative, or clinical remission); aspartate aminotransferase to platelet ratio (APRI) index (<0.7 and ≥0.7); and fibrosis-4 score (<1.45, 1.45-3.25, >3.25).

Results: Metabolic ratio and methadone metabolite concentration in plasma decreased linearly with HCV infection status by the factor of 1.67 (P=0.001) and 2.2 (P=0.043), respectively. Metabolic ratio in plasma decreased in patients with APRI index ≥0.7 by the average factor of 2.12 (P=0.01) and methadone metabolite concentration in plasma decreased by the factor of 6.16 (P=0.009). Metabolic ratio in urine decreased with the severity of fibrosis-4 score by the average factor of 1.63 (P=0.008), whereas methadone metabolite concentration decreased by the factor of 3.53 (P=0.007).

Conclusion: Liver damage decreases methadone metabolism. Indices of liver function should be calculated regularly during MMT for methadone dose titration.