Cannabis and benzodiazepines as determinants of methadone trough plasma concentration variability in maintenance treatment: a transnational study

Relevance of CYP2B6 and CYP2D6 genotypes to methadone pharmacokinetics and response in the OPAL study

AIMS

Our study aimed to evaluate the impacts of the cytochrome P450 (CYP) 2B6-G516T and CYP2D6 genetic polymorphisms on pharmacokinetic and clinical parameters in patients receiving methadone maintenance treatment.

METHODS

Opioid PhArmacoLogy (OPAL) was a clinical survey of the sociodemographic characteristics, history and consequences of pathology associated with methadone maintenance treatment response and current addictive comorbidities. A subgroup of 72 methadone patients was genotyped.

RESULTS

When comparing the three CYP2B6 genotype groups, the methadone (R)- and (S)-methadone enantiomer concentrations/doses (concentrations relative to doses) were different (P = .029, P = .0019). The CYP2D6 phenotypes did not seem to be relevant with regard to methadone levels. On multivariate analysis, neither the CYP2B6 genotype nor the CYP2D6 phenotype explained the (R)-methadone concentration/dose values (P = .92; P = .86); the (S)-methadone concentration/dose values (P = .052; P = .95 [although there was a difference between the TT group and GT and GG groups {P = .019}]); or opiate cessation (P = .12; P = .90).

CONCLUSION

The genotyping of CYP2B6 G516T could be an interesting tool to explore methadone intervariability.

Prevalence of Antipsychotic-Treated Patients in a Cohort of Adult Addicted Patients

PURPOSE

The objective of this cross-sectional study was to describe and estimate the prevalence of antipsychotics (AP) in a cohort of addicted patients, and to compare the profiles of addictive patients receiving AP or not.

METHODS

We included all adult patients seen at the addiction care center of Montpellier University Hospital, between January 1, 2015, and March 31, 2015. Demographic, clinical, and therapeutic data were collected from the patients' medical records.

RESULTS

During the study period, 415 patients were included, with a mean age of 38 ± 10 years. They were mostly men (73.3%), French (54.9%), and unemployed (61.8%). Among the study population, 93 patients (patients treated with AP [trAP], 22.4%) were treated by 111 different AP, mainly cyamemazine (29.0% of treated patients), aripiprazole (20.4%), olanzapine (17.2%), and quetiapine (16.1%), mostly in monotherapy (80.6%) and by oral route (93.2% of AP). Psychiatric history was more frequent in trAP than in those without AP (untrAP) (55.9% vs 35.4% respectively; P < 0.001). Professional activity tended to be less frequent in patients with AP (25.3% vs 38.9%, P = 0.08).When compared with untrAP, trAP consumed more amphetamine (10.8% vs 4.4%; P = 0.02) and tended to consume less opiates (7.5% vs 14.9%; P = 0.06); the consumptions of cannabis (43.0% vs 35.7%; P = 0.20) and cocaine (22.6% vs 16.8%; P = 0.20) were not statistically different.Opiate maintenance therapy was reported in 63.7% of trAP and 68.4% of untrAP (P = 0.41): it consisted of methadone (trAP, 60.3% vs untrAP, 56.5%) and buprenorphine (trAP, 39.7% vs untrAP, 43.5%).

CONCLUSIONS

The concomitant management of psychiatric and substance use disorders in the same center may explain the high prevalence of trAP in this study. Cannabis and psychostimulants may have been used in these patients as self-medication for mental disease-related symptoms or adverse effects of APs.

Polydrug abuse among opioid maintenance treatment patients is related to inadequate dose of maintenance treatment medicine

BACKGROUND

Polydrug abuse is a known problem among opioid-dependent patients receiving opioid maintenance treatment (OMT). However, improved laboratory diagnostics is required to reveal polydrug abuse in its current scope. Furthermore, there are few studies focusing on the relationship between polydrug abuse and adequacy of the dose of OMT medicine. This study aimed to evaluate the polydrug abuse among opioid-dependent patients receiving OMT with inadequate (Group IA) and adequate (Group A) doses of OMT medicine as experienced by the patients. Craving for opioids and withdrawal symptoms were evaluated as indicators of the adequacy rating.

METHODS

This is a retrospective register-based study of 60 OMT patients on either methadone or sublingual buprenorphine/naloxone medication, whose polydrug abuse was studied from urine samples by means of a comprehensive high-resolution mass spectrometry method.

RESULTS

Inadequate doses of the OMT medicines were associated with higher subjective withdrawal scores and craving for opioids. Six groups of abused substances (benzodiazepines, amphetamines, opioids, cannabis, new psychoactive substances, and non-prescribed psychotropic medicines) were found among OMT patients. Group IA patients showed significantly more abuse of benzodiazepines and amphetamines than the Group A patients. All the new psychoactive substances and most of the non-prescribed psychotropic medicines were detected from the Group IA patients. There was no difference in the doses of the OMT medicine between Groups IA and A patients.

CONCLUSIONS

Polydrug abuse, detected by definitive laboratory methods, was widespread and more common among Group IA than Group A patients, emphasizing the requirement for individual OMT medicine dose adjustment.

Relationship between plasma concentrations of the l-enantiomer of methadone and response to methadone maintenance treatment

This study evaluated the relationship between the plasma concentration of l-methadone and response to methadone in real-world patients, in order to identify a minimum plasma concentration above which methadone treatment is effective. Ninety-four patients with opioid dependence under maintenance methadone treatment were consecutively recruited. Response was defined as negative urine analyses in the three weeks prior to the blood sampling. The percentage of participants with a plasma l-methadone concentration between 100 and 250 ng/ml was 54.2% among those with a methadone dosage ≥60 mg/day. Plasma l-methadone concentrations were significantly higher in patients with negative urine analyses compared with those with positive urine analyses (median 93 vs. 77 ng/ml, Mann-Whitney test, P<0.05). Above plasma l-methadone concentrations of 200 ng/ml no heroin use was reported and urine analyses were negative. Moreover, above concentrations of 250 ng/ml craving was absent. Examination of demographic correlates of treatment outcome indicated that older age, a stable job and being married were protective against the use of heroin. Mean plasma l-methadone concentration was significantly lower in patients who used cannabis compared with those who did not use cannabis, after adjusting for methadone dosage. In conclusion our results identify specific cut-offs for plasma l-methadone concentrations about which therapeutic response is observed and provide new evidence that therapeutic response is associated with patient׳s demographic characteristics. This underscores the need to monitor plasma methadone concentrations as part of Drug Addiction Services routine practice, in order to provide an objective framework for changing the methadone dosage.

Impact of cannabis use during stabilization on methadone maintenance treatment

BACKGROUND AND OBJECTIVES

Illicit drug use, particularly of cannabis, is common among opiate-dependent individuals and has the potential to impact treatment in a negative manner.

METHODS

To examine this, patterns of cannabis use prior to and during methadone maintenance treatment (MMT) were examined to assess possible cannabis-related effects on MMT, particularly during methadone stabilization. Retrospective chart analysis was used to examine outpatient records of patients undergoing MMT (n = 91), focusing specifically on past and present cannabis use and its association with opiate abstinence, methadone dose stabilization, and treatment compliance.

RESULTS

Objective rates of cannabis use were high during methadone induction, dropping significantly following dose stabilization. History of cannabis use correlated with cannabis use during MMT but did not negatively impact the methadone induction process. Pilot data also suggested that objective ratings of opiate withdrawal decrease in MMT patients using cannabis during stabilization.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

The present findings may point to novel interventions to be employed during treatment for opiate dependence that specifically target cannabinoid-opioid system interactions.

Respiratory effects of diazepam/methadone combination in rats: a study based on concentration/effect relationships

BACKGROUND

Methadone may cause respiratory depression and fatalities. Concomitant use of benzodiazepines in methadone-treated patients for chronic pain or as maintenance therapy for opiate abuse is common. However, the exact contribution of benzodiazepines to methadone-induced respiratory toxicity remains debatable.

METHODS

We investigated the respiratory effects of the combination diazepam (20mg/kg)/methadone (5mg/kg) in the rat, focusing on methadone concentration/effect relationships. Respiratory effects were studied using arterial blood gases and whole-body plethysmography. Plasma concentrations of both R- and S-methadone enantiomers were measured using high-performance liquid chiral chromatography coupled to mass spectrometry. To clarify mechanisms of diazepam/methadone interaction, methadone metabolism was investigated in vitro using rat liver microsomes.

RESULTS

Diazepam/methadone co-administration significantly increased methadone-related effects on inspiratory time (p<0.001) but did not significantly alter the other respiratory parameters when compared with methadone alone, despite significant increase in the area under the curve of plasma R-methadone concentrations measured during 240 min (p<0.05). Diazepam/methadone co-incubation with microsomes in vitro resulted in a significant inhibition of methadone metabolism (p<0.01), with 50%-inhibitory diazepam concentrations of 25.02 ± 0.18 μmol/L and 25.18 ± 0.23 μmol/L for R- and S-methadone, respectively.

CONCLUSION

We concluded that co-administration of high-doses of diazepam and methadone in rats is not responsible for additional respiratory depression in comparison to methadone alone, despite significant metabolic interaction between the drugs. In humans, although our experimental data may suggest the relative safety of benzodiazepine/methadone co-prescription, physicians should remain cautious as other underlying conditions may enhance this drug-drug interaction.

Pharmacologic evidence to support clinical decision making for peripartum methadone treatment

RATIONALE

Limited pharmacological data are available to guide methadone treatment during pregnancy and postpartum.

OBJECTIVES

Study goals were to (1) characterize changes in methadone dose across childbearing, (2) determine enantiomer-specific methadone withdrawal kinetics from steady state during late pregnancy, (3) assess enantiomer-specific changes in methadone level/dose (L/D) ratios across childbearing, and (4) explore relationships between CYP2B6, CYP2C19, and CYP3A4 single-nucleotide polymorphisms and maternal dose, plasma concentration, and L/D.

METHODS

Methadone dose changes and timed plasma samples were obtained for women on methadone (n = 25) followed prospectively from third trimester of pregnancy to 3 months postpartum.

RESULTS

Participants were primarily white, Medicaid insured, and multiparous. All women increased their dose from first to end of second trimester (mean peak increase = 23 mg/day); 71 % of women increased from second trimester to delivery (mean peak increase = 19 mg/day). Half took a higher dose 3 months postpartum than at delivery despite significantly larger clearance during late pregnancy. Third trimester enantiomer-specific methadone half-lives (range R-methadone 14.7-24.9 h; S-methadone, 8.02-18.9 h) were about half of those reported in non-pregnant populations. In three women with weekly 24-h methadone levels after delivery, L/D increased within 1-2 weeks after delivery. Women with the CYP2B6 Q172 variant GT genotype have consistently higher L/D values for S-methadone across both pregnancy and postpartum.

CONCLUSIONS

Most women require increases in methadone dose across pregnancy. Given the shorter half-life and larger clearances during pregnancy, many pregnant women may benefit from split methadone dosing. L/D increases quickly after delivery and doses should be lowered rapidly after delivery.

Methadone: a review of drug-drug and pathophysiological interactions

Numerous established and potential drug interactions with methadone are clinically important in people treated with methadone either for addiction or for chronic pain. Methadone users often have comorbidities and are prescribed drugs that may interact with methadone. Methadone is extensively metabolized by cytochrome P450 (CYP) 3A4 and to a lesser extent by CYP 1A2, 2D6, 2D8, 2C9/2C8, 2C19, and 2B6. Eighty-six percent of methadone is protein bound, predominately to α1-acid glycoprotein (AGP). Polymorphisms in or interactions with CYPs that metabolize methadone, changes in protein binding, and other pathophysiological conditions affect the pharmacokinetic properties of methadone. It is critical for health care providers who treat patients on methadone to have adequate information on the interactions of methadone with other drugs of abuse and other medications. We set out to describe drug-drug interactions as well as physiological and pathophysiological factors that may impact the pharmacokinetics of methadone. Using MEDLINE, we conducted a systematic search for papers and related abstracts published between 1966 and June 2010. Keywords that included methadone, drug-drug interactions, CYP P450 and AGP identified a total of 7709 papers. Other databases, including the Cochrane Database of Systematic Reviews and Scopus, were also searched; an additional 929 papers were found. Final selection of 286 publications was based on the relevance of each paper to the topic. Over 50 such interactions were found. Interactions of methadone with other drugs can lead to increased or decreased methadone drug levels in patients and result in potential overdose or withdrawal, respectively. The former can contribute to methadone's fatality. Prescribers of methadone and pharmacists should enquire about any new medications (including natural products and over-the-counter medications) periodically, and especially when an otherwise stable patient suddenly experiences drug craving, withdrawal or intoxication.

Hypothalamic opioid-melanocortin appetitive balance and addictive craving

Whilst the parallels between drug and food craving are receiving increasing attention, the recently elucidated complex physiology of the hypothalamic appetite regulatory centres has been largely overlooked in the efforts to understand drug craving which is one of the most refractory and problematic aspects of drug and behavioural addictions. Important conceptual gains could be made by researchers from both appetite and addiction neuroscience if they were to have an improved understanding of each others' disciplines. It is well known in addiction medicine that the use of many substances is elevated in opiate dependency. There is voluminous evidence of very high rates of drug use in opiate agonist maintained patients, and the real possibility exists that opiate agonist therapy therefore increases drug craving. Conversely, opiate antagonist therapy with naloxone or naltrexone has been shown to reduce most chemical and behavioural addictions, and naltrexone is now being developed together with bupropion as the anti-obesity drug "Contrave". Hypothalamic melanocortins, particularly α-MSH, are known to constitute the main brake to consumptive behaviour of food. There is a well described antagonism between melanocortins and opioids at many loci including the hypothalamus. Administration of exogenous opiates is known to both suppress α-MSH and to stimulate hedonic food consumption. Opiate maintenance programs are associated with weight gain. As monoamines, opioids and cannabinoids are known to be involved in appetite regulation, and as endorphin opioids are known to be perturbed in other addictions, further exploration of the hypothalamic appetite regulatory centre would appear to be an obvious, albeit presently largely overlooked, locus in which to study drug and other craving mechanisms.