Evaluation of levo-alpha-acetylmethdol (LAAM) as an alternative treatment for methadone maintenance patients who regularly experience withdrawal: a pharmacokinetic and pharmacodynamic analysis

Current and emerging pharmacotherapies for opioid dependence treatments in adults: a comprehensive update

INTRODUCTION

Opioid use disorder (OUD) is characterized by compulsive opioid seeking and taking, intense drug craving, and intake of opioids despite negative consequences. The prevalence of OUDs has now reached an all-time high, in parallel with peak rates of fatal opioid-related overdoses, where 15 million individuals worldwide meet the criteria for OUD. Further, in 2020, 120,000 opioid-related deaths were reported worldwide with over 75,000 of those deaths occurring within the United States.

AREAS COVERED

In this review, we highlight pharmacotherapies utilized in patients with OUDs, including opioid replacement therapies, and opioid antagonists utilized for opioid overdoses and deterrent of opioid use. We also highlight newer treatments, such as those targeting the neuroimmune system, which are potential new directions for research given the recently established role of opioids in activating neuroinflammatory pathways, as well as over the counter remedies, including kratom, that may mitigate withdrawal.

EXPERT OPINION

To effectively treat OUDs, a deeper understanding of the current therapeutics being utilized, their additive effects, and the added involvement of the neuroimmune system are essential. Additionally, a complete understanding of opioid-induced neuronal alterations and therapeutics that target these abnormalities - including the neuroimmune system - is required to develop effective treatments for OUDs.

m-Trifluoromethyl-diphenyl diselenide (m-CF3-PhSe)2 modulates the hippocampal neurotoxic adaptations and abolishes a depressive-like phenotype in a short-term morphine withdrawal in mice

The opioid withdrawal syndrome is defined as a complex phenomenon involving multiple cellular adaptations, which leads to the emergence of aversive physical and affective signs. The m-trifluoromethyl-diphenyl diselenide (m-CF₃-PhSe)₂ elicits an antidepressant-like effect by modulating the opioid system in different animal models of mood disorders. Notably, repeated exposure to (m-CF₃-PhSe)₂ developed neither tolerance nor withdrawal signs in mice. The aim of the present study was to investigate whether (m-CF₃-PhSe)₂ attenuates the physical signs and the depressive-like phenotype during morphine withdrawal through its neuroprotective effects on oxidative stress, the NMDA receptor and the proBDNF/mBDNF signaling in the hippocampus of mice. Adult Swiss mice received saline solution or escalating doses (20-100 mg/kg, sc) of morphine for six days. For the next three days, the animals were treated with canola oil, (m-CF₃-PhSe)₂ (5 and 10 mg/kg, ig) or methadone (5 mg/kg, sc) whereas morphine injections were discontinued. On day 9, physical withdrawal signs and depressive-like behavior were assessed 30 min after the last administration of (m-CF₃-PhSe)_2. Although short-term treatment with (m-CF₃-PhSe)₂ at both doses suppressed the aversive physical and affective signs in morphine withdrawn-mice, the highest dose of (m-CF₃-PhSe)₂ per se increased the teeth chattering manifestation. The intrinsic antioxidant property of (m-CF₃-PhSe)₂ modulated oxidative stress, it also restored the NMDA receptor levels in the hippocampus of morphine withdrawn-mice. Besides, (m-CF₃-PhSe)₂ downregulated the proBDNF/p-75^NTR/JNK pro-apoptotic pathway without affecting the mBDNF/TrkB/ERK/CREB pro-survival signaling in the hippocampus of morphine withdrawn-mice. The results show that (m-CF₃-PhSe)₂ treatment modulated the hippocampal neurotoxic adaptations and abolished the depressive-like phenotype following morphine withdrawal in mice.

Treadmill exercise attenuates the severity of physical dependence, anxiety, depressive-like behavior and voluntary morphine consumption in morphine withdrawn rats receiving methadone maintenance treatment

This study was designed to examine whether treadmill exercise would attenuate the severity of physical dependence, methadone-induced anxiety, depression and voluntary morphine consumption in morphine withdrawn rats receiving methadone maintenance treatment (MMT). The rats were chronically treated with bi-daily doses (10 mg/kg, at 12 h intervals) of morphine for 14 days. The exercising rats receiving MMT were forced to run on a motorized treadmill for 30 days during morphine withdrawal. Then, rats were tested for the severity of morphine dependence, the elevated plus-maze (EPM), sucrose preference test (SPT) and voluntary morphine consumption using a two-bottle choice (TBC) paradigm. The results showed that naloxone- precipitated opioid withdrawal signs were decreased in exercising morphine-dependent rats receiving MMT than sedentary rats. Also, the exercising morphine-dependent rats receiving MMT exhibited an increased time on open arms, preference for sucrose and a lower morphine preference ratio than sedentary rats. We conclude that treadmill exercise decreased the severity of physical dependence, anxiety/depressive-like behaviors and also the voluntary morphine consumption in morphine withdrawn rats receiving MMT. Thus, exercise may benefit in the treatment of addicts during MMT.

Advances in the delivery of buprenorphine for opioid dependence

Opioid use disorders (OUDs) have long been a global problem, but the prevalence rates have increased over 20 years to epidemic proportions in the US, with concomitant increases in morbidity and all-cause mortality, but especially opioid overdose. These increases are in part attributable to a several-fold expansion in the prescription of opioid pain medications over the same time period. Opioid detoxification and psychosocial treatments alone have each not yielded sufficient efficacy for OUD, but μ-opioid receptor agonist, partial agonist, and antagonist medications have demonstrated the greatest overall benefit in OUD treatment. Buprenorphine, a μ-opioid receptor partial agonist, has been used successfully on an international basis for several decades in sublingual tablet and film preparations for the treatment of OUD, but the nature of formulation, which is typically self-administered, renders it susceptible to nonadherence, diversion, and accidental exposure. This article reviews the clinical trial data for novel buprenorphine delivery systems in the form of subcutaneous depot injections, transdermal patches, and subdermal implants for the treatment of OUD and discusses both the clinical efficacy of longer-acting formulations through increasing consistent medication exposure and their potential utility in reducing diversion. These new delivery systems also offer new dosing opportunities for buprenorphine and strategies for dosing intervals in the treatment of OUD.

Cardiotoxicity of Oral Methadone as an Analgesic–-Recommendations for Safe Use

Once used only as third-line therapy in the management of chronic pain states, methadone is now being used as first- and second-line therapy. Most risks and the stigma associated with methadone use have been known for years. Only over the past decade or so have the unique pharmacokinetic-pharmacodynamic properties and methods for conversion from other opioids to methadone been established. Pertinent English-language literature was obtained from MEDLINE/PUBMED and EMBASE searches (1966-June 2009). This paper provides an overview of the cardiotoxicity of oral methadone, with an emphasis on its use as an analgesic. Cardiotoxicity during its use in the maintenance of opioid addiction has also been reviewed due to the wealth of epidemiologic, risk factor, and correlative analytic data contained therein. A series of recommendations are provided to improve the cardiac safety profile of oral methadone used for analgesia. In addition, there is a discussion of settings and patient types which may impact upon these recommendations.

The operational multiple dosing half-life: a key to defining drug accumulation in patients and to designing extended release dosage forms

Half-life (t (1/2)) is the oldest but least well understood pharmacokinetic parameter, because most definitions are related to hypothetical 1-compartment body models that don't describe most drugs in humans. Alternatively, terminal half-life (t (1/2,z)) is utilized as the single defining t (1/2) for most drugs. However, accumulation at steady state may be markedly over predicted utilizing t (1/2, z). An apparent multiple dosing half-life (t (1/2, app)) was determined from peak and trough steady-state ratios and found to be significantly less than reported terminal t (1/2)s for eight orally dosed drugs with t (1/2,z) values longer than one day. We define a new parameter, "operational multiple dosing half-life" (t (1/2, op)), as equal to the dosing interval at steady-state where the maximum concentration at steady-state is twice the maximum concentration found for the first dose. We demonstrate for diazepam that the well-accepted concept that t (1/2,z) representing the great majority of the AUC will govern accumulation can be incorrect. Using oral diazepam, we demonstrate that t (1/2, op) is remarkably sensitive to the absorption t (1/2), even when this absorption t (1/2) is much less than t (1/2,z,) and describe the relevance of this in designing extended release dosage forms. The t (1/2, op) is compared with previously proposed half-lives for predicting accumulation.

Role of active metabolites in the use of opioids

The opioid class of drugs, a large group, is mainly used for the treatment of acute and chronic persistent pain. All are eliminated from the body via metabolism involving principally CYP3A4 and the highly polymorphic CYP2D6, which markedly affects the drug's function, and by conjugation reactions mainly by UGT2B7. In many cases, the resultant metabolites have the same pharmacological activity as the parent opioid; however in many cases, plasma metabolite concentrations are too low to make a meaningful contribution to the overall clinical effects of the parent drug. These metabolites are invariably more water soluble and require renal clearance as an important overall elimination pathway. Such metabolites have the potential to accumulate in the elderly and in those with declining renal function with resultant accumulation to a much greater extent than the parent opioid. The best known example is the accumulation of morphine-6-glucuronide from morphine. Some opioids have active metabolites but at different target sites. These are norpethidine, a neurotoxic agent, and nordextropropoxyphene, a cardiotoxic agent. Clinicians need to be aware that many opioids have active metabolites that will become therapeutically important, for example in cases of altered pathology, drug interactions and genetic polymorphisms of drug-metabolizing enzymes. Thus, dose individualisation and the avoidance of adverse effects of opioids due to the accumulation of active metabolites or lack of formation of active metabolites are important considerations when opioids are used.

Levo-alpha-acetylmethadol (LAAM) versus methadone maintenance: 1-year treatment retention, outcomes and status

AIMS

To compare levo-alpha-acetylmethadol (LAAM) and methadone maintenance (MM) on treatment retention, drug use during treatment and at follow-up, and abstinence.

DESIGN

A two-group experimental design with patients assigned randomly (2:1) to receive fully subsidized LAAM or MM for 52 weeks.

SETTING

A community clinic providing maintenance treatment in Los Angeles, California.

PARTICIPANTS

A total of 315 treatment-seeking patients willing to be assigned randomly to treatment condition; 289 (91.7%) were interviewed at 52 weeks.

INTERVENTION

LAAM or MM, plus ancillary services available to all patients. Medication dose varied according to clinical judgement.

MEASUREMENTS

Treatment retention and status at 52-week follow-up, weekly clinical urinalysis, self-reported drug use and research urinalysis on samples collected at follow-up.

FINDINGS

LAAM participants were more likely to complete the planned 52 weeks (57.4%) than MM participants (46.2%) and were less likely to be discharged for arrest/incarceration. LAAM produced fewer during treatment clinic opiate-positive samples (M = 48.8) than MM (M = 62.3). Further, 24.4% on LAAM compared to 11.8% on MM were able to sustain at least 12 weeks of abstinence during the last 24 weeks of treatment. Opiate use at follow-up was lowest (50.9%) among LAAM participants in maintenance treatment. No adverse events, cardiological or otherwise, were observed with LAAM administration.

CONCLUSIONS

LAAM is an effective medication for the treatment of opiate dependence in community clinics with numerous behavioral and clinical advantages. LAAM is more effective than MM in promoting retention and extended reduction in and abstinence from opiate use while in treatment.

Blood-brain equilibration kinetics of levo-alpha-acetyl-methadol using a chronically instrumented sheep preparation

1.--The delayed onset and long duration of action of the opioid agonist levo-alpha-acetyl-methadol (LAAM) has been attributed to the formation of active metabolites. However, at present, little is known about the time course of blood-brain equilibration of LAAM itself. 2.--The cerebral kinetics of LAAM were quantified using physiologically based kinetic models and a conscious chronically instrumented sheep preparation. Seven sheep were administered 4 min intravenous infusions of 30 mg LAAM. Concentrations of LAAM and N-demethylated metabolites (nor-LAAM and di-nor-LAAM) in whole blood (0-75 min) were measured using a validated HPLC assay. 3.--LAAM did not alter cerebral blood flow, mean arterial pressure or cause significant respiratory depression. Cardiac output was similar to baseline at 4 min, but decreased by 30% at 10 min and remained at this level for the duration of the 75 min study period. 4.--Cerebral kinetics were best described by a membrane-limited model, with a relatively slow blood-brain tissue equilibration half-life of 22 min due to intermediate permeability (56 ml min(-1)) and a large cerebral distribution volume (724 ml). 5.--In conclusion, pharmacokinetic-pharmacodynamic modelling of LAAM should account for the large equilibration delay between brain and blood caused by slow equilibration kinetics. This may account for some of the delay in onset of effect previously attributed to the delayed appearance of active metabolites in blood.

HIV risk behaviors during pharmacologic treatment for opioid dependence: A comparison of levomethadyl acetate hydrochloride, buprenorphine, and methadone

The efficacies of three opioid substitution medications for reducing HIV risk behaviors in opioid-dependent patients were assessed in a randomized double-blind clinical trial comparing levomethadyl acetate [corrected] (LAAM), buprenorphine (BUP), and methadone (METH). Individually optimized flexible dosing was used for each group, with weekly possible doses of 255-391 mg of LAAM, 56-112 mg of BUP, and 420-700 mg of METH. An interview regarding specific HIV risk behaviors, including injecting, equipment sharing, and sexual activity, yielded data for pretreatment and four in-study time points for 137 subjects. Declines in risk behaviors during treatment were evident in all groups for most measures of injecting and equipment sharing. Only the METH group showed consistent declines in measures of sexual behaviors. These results demonstrate that all three medications can be highly effective in decreasing HIV risk behaviors when the dose is optimized. Reductions in sexual behaviors for the METH group are consistent with known METH side effects.

Within- and between- subject variability in methadone pharmacokinetics and pharmacodynamics in methadone maintenance subjects

AIMS

To investigate within- and between-subject variability of the pharmacodynamics and pharmacokinetics of (R)- and (S)-methadone in methadone maintenance subjects at steady-state.

METHODS

Six non-holder subjects were studied on three occasions at 7-16 day intervals; doses (20-170 mg/day) remained unchanged. Blood samples and pharmacodynamic data were collected 10-12 times over a 24-h inter-dosing interval. All pharmacodynamic data were expressed as the area under the end-point versus time curve. Using analyses of variance with mixed effects, best estimates were made of the ratio of between- to within-subject variation, with corresponding 95% confidence intervals (CI) for within-subject variation at the average value.

RESULTS

Subjects were relatively consistent between occasions, whereas there was much greater between-subject variability (P < 0.02) for all measures. Estimates of the ratio of between- to within-subject variation ranged from 2.2-12.8 for pharmacodynamic measures, and 1.3-7.9 for pharmacokinetic parameters. For pain, total mood disturbance, withdrawal, pupil size and respiration rate, 95% CI for within-subject measures ranged < or = 2-fold, while this was greater for subjective direct opioid effects (4.2-fold). For CL/F of the active (R)-methadone, the variance ratio was 4.9 (P < 0.0003), with 95% CI for within-subject measures ranging < or = 2-fold. (S)-methadone CL/F demonstrated greater within-subject variability (3.4-fold), possibly contributing to a smaller (2.7; P < 0.0003) ratio of between- to within-subject variance.

CONCLUSIONS

Non-holder methadone maintenance treatment participants appear to respond consistently with respect to pharmacokinetics and pharmacodynamics over a 1-2 month period. Such knowledge may help prescribers to determine whether alternative dosing regimens or treatments might be more appropriate in this population.

Fluctuations in (R,S)-methadone pharmacokinetics and response among long-term methadone maintenance patients

Knowledge of how methadone disposition may fluctuate during the course of maintenance treatment is presently limited. This study investigated long-term fluctuations in methadone pharmacokinetics in five methadone maintenance patients who participated in two 24-hour testing sessions separated by at least one year. Results indicated substantial fluctuations between sessions in dose-corrected average steady-state plasma (R)-methadone concentrations (Cav), ranging from a 51% decrease to a 466% increase. These fluctuations were not consistently associated with changes in methadone dose or self-reported withdrawal status. The plasma (S)-:(R)-methadone Cav ratio increased significantly (12%, P = 0.04) between the sessions, suggesting a different pattern of long-term change in the pharmacokinetics of each enantiomer over time. The pronounced and variable fluctuations in methadone disposition evident in these patients highlight the need for an individualized approach to patient dosing and monitoring.