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

Methadone metabolism and cytochrome P450 polymorphisms: a systematic review and meta-analysis

INTRODUCTION

Confusion regarding methadone metabolism exists, hampering optimal clinical use. A systematic review was conducted to assess the impacts of cytochrome P450 (CYP) genetic polymorphisms on methadone outcomes.

METHODS

MEDLINE, EMBASE, Web of Science, PsycINFO, and CENTRAL were searched to identify studies reporting methadone dose-adjusted plasma concentrations, clearance, maintenance dose, or treatment response in relation to CYP polymorphisms in humans. ROBINS-I was used to evaluate risk of bias in included studies. Each outcome was synthesized for each CYP using the ratio of means or odds ratio as the effect size measure.

RESULTS

Ten, two, fourteen, and five studies were included in the meta-analyses of the concentration, clearance, dose, and treatment response, respectively. The CYP2B6 c.516 G>T variant was robustly associated with (S)-methadone concentrations (GT+TTvs.GG: ratio of means (RoM) 1.40, p < 0.01) and clearance (GT+TTvs.GG: RoM 0.65, p < 0.01) but less with (R)- or (R,S)-methadone. The CYP2B6 variant also affected methadone dose for opioid use disorder (GT+TTvs.GG: RoM 0.93, p = 0.04). CYP2C19, CYP2C9, CYP2D6, and CYP3A5 polymorphisms did not influence any of the assessed outcomes.

CONCLUSIONS

CYP2B6 genetics had statistically significant impacts on (S)-methadone and less so on (R)-methadone exposure and clearance and was statistically significantly but not clinically meaningfully associated with dose requirements.

Pharmacokinetics, Tolerability, and Safety of Esmethadone in Subjects with Chronic Kidney Disease or Hepatic Impairment

BACKGROUND AND OBJECTIVES

Esmethadone (dextromethadone; d-methadone; S-methadone (+)-methadone; REL-1017) is a low potency N-methyl-D-aspartate (NMDA) receptor channel blocker that showed a rapid and sustained adjunctive antidepressant effects in patients with major depressive disorder with inadequate response to ongoing serotonergic antidepressant treatment. Previous studies indicated that esmethadone is partially excreted by the kidney (53.9% of the dose) and by the liver (39.1% of the dose).

METHODS

Here we studied the pharmacokinetics and safety of esmethadone after a single oral dose of 25 mg in subjects with different stages of kidney and liver impairment.

RESULTS

In subjects with a mild and moderate decrease in glomerular fraction rate (GFR), esmethadone Cmax and AUC0-inf values did not differ compared with healthy subjects. In patients with severe renal impairment, the ratios of Cmax and AUC0-inf values compared with healthy subjects were above 100% (138.22-176.85%) and, while modest, these increases reached statistical significance. In subjects with end stage renal disease (ESRD) undergoing intermittent hemodialysis (IHD), Cmax and AUC0-inf values were not statistically different compared with healthy subjects. IHD did not modified plasma total esmethadone concentrations in blood exiting versus entering the dialyzer. Dose adjustment is not warranted in subjects with mild-to-moderate impaired renal function. Dose reduction may be considered for select patients with severe renal disfunction. In subjects with mild-or-moderate hepatic impairment, Cmax and AUC0-inf were approximately 20-30% lower compared with healthy controls. The drug free fraction increased with the severity of hepatic impairment, from 5.4% in healthy controls to 8.3% in subjects with moderate hepatic impairment.

CONCLUSION

Mild and moderate hepatic impairment has a minimal to modest impact on exposure to total or unbound esmethadone and dose adjustments are not warranted in subjects with mild and moderate hepatic impairment. Administration of esmethadone was well tolerated in healthy adult subjects, in subjects with mild or moderate hepatic impairment, and in subjects with mild moderate or severe renal impairment, including patients with ESRF undergoing dialysis.

Methadone pharmacokinetics in opioid agonist treatment: Influencing factors and clinical implications

BACKGROUND

A considerable inter-individual variability has been reported in the relationship between methadone doses applied and serum concentrations achieved in methadone maintenance treatment. However, the underlying causes for this variability are not fully understood.

OBJECTIVES

We investigated the influence of genetic, pathophysiological and pharmacological factors on serum methadone concentration-to-dose ratio (CDR) and discussed the clinical implications of the findings.

METHODS

We used data from two retrospective laboratory databases and a prospective cohort study to investigate the impact on methadone CDR of hepatic cytochrome P450 enzyme system (CYP) genetic polymorphisms, age, sex, concomitant medication, liver fibrosis and body mass index through linear mixed model analyses.

FINDINGS

A positive association was found between CDR and the homozygous CYP2B6*6 genotype, concurrent treatment with CYP3A4 inhibitors and body mass index. CDR was lower among women and during concomitant use of CYP inducers. CDR was not associated with age or the degree of liver fibrosis in our investigations.

CONCLUSIONS

This research work supports the need for individually tailored dosage considering the various factors that influence methadone CDR. The gained knowledge can contribute to reducing the risks associated with the treatment and optimizing the desired outcomes.

Levomethadone Therapeutic Drug Monitoring to Aid Opioid Withdrawal Therapy: A Short Communication

BACKGROUND

Therapeutic drug monitoring (TDM) is recommended for opioid maintenance therapy with levomethadone. However, TDM has not yet been applied to monitor opioid withdrawal therapy clinically, although tools to improve it are required.

METHODS

In this observational cohort study, repeated TDM with levomethadone was performed according to a prospective opioid withdrawal study protocol. Objective and subjective opioid withdrawal symptoms were measured using validated rating scales and correlated to levomethadone plasma concentrations. Plasma levels were measured using high-pressure liquid chromatography with column switching and spectroscopic detection of methadone and its major metabolite.

RESULTS

This study included 31 opioid-dependent patients who participated in standardized opioid withdrawal therapy. The serum levels of levomethadone were found to be highly variable and below the recommended therapeutic reference range of 250 ng/mL for maintenance therapy. These serum levels were positively correlated with dosage (r = 0.632; P < 0.001) and inversely correlated with subjective (r = -0.29; P = 0.011) and objective (r = -0.28; P = 0.014) withdrawal symptoms.

CONCLUSIONS

The evidence provided sheds light on how to improve levomethadone withdrawal therapy in patients with opioid dependence. It seems likely that higher initial doses at the beginning and lower dose reductions would have been advantageous. TDM can enhance the safety of opioid withdrawal therapies, minimize withdrawal symptoms, and reduce dropout rates.