Prospective Study of QTc Changes Among Former Opiate Addicts Since Admission to Methadone Maintenance Treatment: Benzodiazepine Risk

Influence of CYP2B6 Genotype on Methadone Dosage in Patients from the Methadone Maintenance Treatment (MMT) Program in Pereira, Colombia

Methadone treatment reduces the use of heroin and withdrawal symptoms; however, methadone is an expensive medication with a narrow safety margin. We compared the retention rates, persistence of heroin use, and quality of life of a group of patients undergoing conventional Methadone Maintenance Treatment (MMT) with a group for whom the CYP2B6 516G>T polymorphism was used in addition to the MMT to calculate the required methadone dose. Over 12 weeks, the retention rate, heroin usage, and quality of life of patients under conventional treatment (n = 34) were compared with those of patients for whom we used genetic markers to calculate methadone dosage (n = 38). At the end of the study, 26.4% of patients abandoned the program, and neither demographic nor clinical variables were associated with treatment adherence. Of the remaining patients, 16% of the control group and 8% of patients in the pharmacogenetic group reported heroin use, while both groups showed a 64% reduction in the use of cocaine/crack (no significant differences between the groups were found). Starting in the second week, the methadone dosage was lower among the patients for whom methadone was prescribed based on genotype. Although there were six individuals in the control group and three in the pharmacogenetic group with QTc intervals > 450 ms (a threshold that is considered dangerous), we did not find a relationship between the QTc interval and methadone dosage. There were no differences in the perception of quality of life between the two groups. The results of this pilot study suggest that concerning methadone therapy, the CYP2B6 genotype contributes to reduced effective doses and treatment costs.

Methadone and the QTc Interval: Paucity of Clinically Significant Factors in a Retrospective Cohort

OBJECTIVE

Methadone is associated with prolongation of the electrocardiographic QTc interval. QTc prolongation may be linked to cardiac dysrhythmia and sudden cardiac death. The rate of these events is unknown in methadone-maintained patients.

METHODS

This retrospective cohort study of 749 patients with opioid use disorder receiving methadone maintenance therapy through a single safety-net hospital, queried the electronic health record for electrocardiogram results, demographics, methadone dose, and diagnostic codes consistent with cardiac conduction disorder (International Classification of Disease, Ninth Revision [ICD-9] 426) and cardiac dysrhythmia (ICD-9 427). Factors associated with QTc interval were explored; Cox proportional-hazards regression models were used to analyze time to an event that may predispose to sudden cardiac death.

RESULTS

One hundred thirty-four patients had an electrocardiogram while on methadone, 404 while off methadone, and 211 both while on and off methadone. Mean QTc interval while on methadone (436 ms, SD 36) was significantly greater than while off methadone (423 ms, SD 33). Age and methadone dose were weakly associated with increased QTc interval (P < 0.01 and P < 0.0005, respectively, adjusted R = 0.05). There were 44 ICD-9 426 and 427 events over 7064 patient-years (6.3 events/1000 patient-yrs). Having a QTc greater than sex-specific cut-off values was significantly associated with time to event (hazard ratio 3.32, 95% confidence interval 1.25-8.81), but being on methadone was not.

CONCLUSIONS

Methadone is associated with QTc prolongation in a nonclinically significant dose-related manner. Cardiac events were rare and the sudden cardiac death rate was below that of the general population. Current recommendations for cardiac risk assessment in methadone-maintained patients should be reconsidered.

Effects of cytochrome P450 single nucleotide polymorphisms on methadone metabolism and pharmacodynamics

Methadone is a synthetic, long-acting opioid with a single chiral center forming two enantiomers, (R)-methadone and (S)-methadone, each having specific pharmacological actions. Concentrations of (R)- and (S)-methadone above therapeutic levels have the ability to cause serious, life-threatening, and fatal side effects. This toxicity can be due in part to the pharmacogenetics of an individual, which influences the pharmacokinetic and pharmacodynamic properties of the drug. Methadone is primarily metabolized in the liver by cytochrome P450 (CYP) enzymes, predominately by CYP2B6, followed by CYP3A4, 2C19, 2D6, and to a lesser extent, CYP2C18, 3A7, 2C8, 2C9, 3A5, and 1A2. Single nucleotide polymorphisms (SNPs) located within CYPs have the potential to play an important role in altering methadone metabolism and pharmacodynamics. Several SNPs in the CYP2B6, 3A4, 2C19, 2D6, and 3A5 genes result in increases in methadone plasma concentrations, decreased N-demethylation, and decreased methadone clearance. In particular, carriers of CYP2B6*6/*6 may have a greater risk for detrimental adverse effects, as methadone metabolism and clearance are diminished in these individuals. CYP2B6*4, on the other hand, has been observed to decrease plasma concentrations of methadone due to increased methadone clearance. The involvement, contribution, and understanding the role of SNPs in CYP2B6, and other CYP genes, in methadone metabolism can improve the therapeutic uses of methadone in patient outcome and the development of personalized medicine.

Long QTc During Methadone Maintenance: Contributors and Interventions Over 4 Years

Our goal consisted of describing the 4-year prevalence, contributors, and interventions for long QTc's in methadone maintenance treatment. Cardiologists' diagnosis of long QTc defined case-ness in 62 patients. Long QTc categories, drawn from epidemiological reports, encompassed 440 to 469 (borderline), 470 to 499 (moderate), and 500+ milliseconds (severe). Data collection included electrocardiograms, demographic characteristics, contributors to long QTc, and interventions-plus-outcomes (defined by resolution of long QTc). Of 62 patients, 21 had 39 long QTc episodes-a 4-year case prevalence of 34%, and an annual episode incidence of 15.7 per 100. Contributing factors identified in 36 of 39 episodes consisted of medication management (n = 19), illicit drug use (n = 11), and other factors (n = 6). Long QTc reverted to normal in 38 of 39 episodes. Of 21 patients, 12 (57%) experienced one or two recurrences. Methadone maintenance treatment physicians normalized most episodes as outpatients, often in collaboration with patients' primary care physicians. One fifth of episodes required hospitalization and other specialty care. Lack of timely QTc normalization may have accounted for one sudden death.

QT interval prolongation in opioid agonist treatment: analysis of continuous 12-lead electrocardiogram recordings

AIMS

Methadone is a widely used opioid agonist treatment associated with QT prolongation and torsades de pointes. We investigated the QT interval in patients treated with methadone or buprenorphine using continuous 12-lead Holter recordings.

METHODS

We prospectively made 24-h Holter recordings in patients prescribed methadone or buprenorphine, compared to controls. After their normal dose a continuous 12-lead Holter recorder was attached for 24 h. Digital electrocardiograms were extracted hourly from the Holter recordings. The QT interval was measured automatically (H-scribe software, Mortara Pty Ltd) and checked manually. The QT interval was plotted against heart rate (HR) on the QT nomogram to determine abnormality. Demographics, dosing, medical history and laboratory investigations were recorded.

RESULTS

There were 58 patients (19 methadone, 20 buprenorphine and 19 control); median age 35 years (20-56 years); 33 males. Baseline characteristics were similar. Median dose of methadone was 110 mg day-1 (70-170 mg day-1 ) and buprenorphine was 16 mg day-1 (12-32 mg day-1 ). Seven participants had abnormal QT intervals. There was a significant difference in the proportion of prescribed methadone with abnormal QT intervals, 7/19 (37%; 95% confidence interval: 17-61%), compared to controls 0/19 (0%; 95% confidence interval: 0-21%; P = 0.008), but no difference between buprenorphine and controls (0/20). QT vs. HR plots showed patients prescribed methadone had higher QT-HR pairs over 24 h compared to controls. There was no difference in dose for patients prescribed methadone with abnormal QT intervals and those without.

CONCLUSIONS

Methadone is associated with prolonged QT intervals, but there was no association with dose. Buprenorphine did not prolong the QT interval. Twenty four-hour Holter recordings using the QT nomogram is a feasible method to assess the QT interval in patients prescribed methadone.

Cardiovascular effects of methadone and concomitant use of diazepam during methadone maintenance treatment induction: low concentration risk

BACKGROUND

The aim is to evaluate the role of diazepam concentrations in development of low-concentration-methadone-associated QTc prolongation in patients with opioid use disorder during methadone maintenance treatment (MMT) induction.

RESEARCH DESIGN AND METHODS

Individuals with addiction disorder on MMT were studied before the beginning of MMT and after one and six months of MMT. Serum concentrations of methadone, diazepam, electrolytes and ECG were analyzed.

RESULTS

Thirty patients were enrolled. The mean methadone concentration at time points was 177 ± 119 ng/ml and 343 ± 182 ng/ml, while the mean diazepam concentration was 561 ± 437 ng/ml and 1045 ± 933 ng/ml. The QTc interval before the introduction of MMT, after 1 and 6 months of MMT were 412 ± 27 ms, 425 ± 18 ms and 424 ± 15 ms, respectively, showing statistically significant increase in the length of QTc interval after 1 and 6 months of MMT. Statistically significant correlation between the concentration of methadone and QTc interval length at observed time points (R² = 0.239, p = 0.018; R² = 0.513, p = 0.006) was shown, and it remained so if the concentration of diazepam was included (R² = 0.347, p = 0.026, R² = 0.513, p = 0.009).

CONCLUSIONS

The prolongation of QTc below the risk threshold in low methadone therapeutic doses has been recorded and concomitant use of diazepam could be a co-factor in such issue.