The use of plasma levels to optimize methadone maintenance treatment

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.

GC-MS Analysis of Methadone and EDDP in Addicted Patients under Methadone Substitution Treatment: Comparison of Urine and Plasma as Biological Samples

(1) Background: Methadone, along with buprenorphine, is the most commonly used drug for the treatment of opioid dependence. This study aimed to analyze methadone and its major metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenyl pyrrolidine (EDDP), in the urine and plasma of opiate addicts. The study group consisted of drug users voluntarily admitted to the detoxification center C.E.T.T.T. "St. Stelian" of Bucharest. Secondly, the study aimed to identify whether urine or plasma provides better results for the proposed method. (2) Methods: A GC-MS method, using an internal standard (diphenylamine) in the FULL-SCAN and SIM modes of operation and using the m/z = 72 ion for methadone and the m/z = 277 ion for EDDP, combined with a liquid-liquid extraction procedure was performed. (3) Results: The applied procedure allows the detection and quantification of methadone in both urine and plasma samples. EDDP was identified in patients with higher levels of methadone. Higher levels of methadone were detected in urine than in plasma samples. (4) Conclusions: This procedure can be used in clinical laboratories for the rapid determination of methadone levels in urine rather than in plasma. The procedure can be applied for the monitoring of methadone substitution treatment.

Wearable Electrochemical Sensors for the Monitoring and Screening of Drugs

Wearable electrochemical sensors capable of noninvasive monitoring of chemical markers represent a rapidly emerging digital-health technology. Recent advances toward wearable continuous glucose monitoring (CGM) systems have ignited tremendous interest in expanding such sensor technology to other important fields. This article reviews for the first time wearable electrochemical sensors for monitoring therapeutic drugs and drugs of abuse. This rapidly emerging class of drug-sensing wearable devices addresses the growing demand for personalized medicine, toward improved therapeutic outcomes while minimizing the side effects of drugs and the related medical expenses. Continuous, noninvasive monitoring of therapeutic drugs within bodily fluids empowers clinicians and patients to correlate the pharmacokinetic properties with optimal outcomes by realizing patient-specific dose regulation and tracking dynamic changes in pharmacokinetics behavior while assuring the medication adherence of patients. Furthermore, wearable electrochemical drug monitoring devices can also serve as powerful screening tools in the hands of law enforcement agents to combat drug trafficking and support on-site forensic investigations. The review covers various wearable form factors developed for noninvasive monitoring of therapeutic drugs in different body fluids and toward on-site screening of drugs of abuse. The future prospects of such wearable drug monitoring devices are presented with the ultimate goals of introducing accurate real-time drug monitoring protocols and autonomous closed-loop platforms toward precise dose regulation and optimal therapeutic outcomes. Finally, current unmet challenges and existing gaps are discussed for motivating future technological innovations regarding personalized therapy. The current pace of developments and the tremendous market opportunities for such wearable drug monitoring platforms are expected to drive intense future research and commercialization efforts.

Against Repurposing Methadone for Glioblastoma Therapy

Methadone, which is used as maintenance medication for outpatient treatment of opioid dependence or as an analgesic drug, has been suggested by preclinical in vitro and mouse studies to induce cell death and sensitivity to chemo- or radiotherapy in leukemia, glioblastoma, and carcinoma cells. These data together with episodical public reports on long-term surviving cancer patients who use methadone led to a hype of methadone as an anti-cancer drug in social and public media. However, clinical evidence for a tumoricidal effect of methadone is missing and prospective clinical trials, except in colorectal cancer, are not envisaged because of the limited preclinical data available. The present article reviews the pharmacokinetics, potential molecular targets, as well as the evidence for a tumoricidal effect of methadone in view of the therapeutically achievable doses in the brain. Moreover, it provides original in vitro data showing that methadone at clinically relevant concentrations fails to impair clonogenicity or radioresistance of glioblastoma cells.

Dose, Plasma Level, and Treatment Outcome Among Methadone Patients in Shanghai, China

The purpose of this study was to investigate the blood levels of methadone in participants receiving methadone for the treatment of opioid dependence. After stabilization on methadone for four weeks, blood samples from 95 participants were collected between treatment weeks 4 and 12, before and after receiving doses of methadone, and its blood levels were measured. A multiple linear regression model was used to examine the association between methadone blood levels and the outcomes of methadone maintenance treatment (MMT). Outcome differences between participants who had high (≥2) or low (<2) peak-to-trough ratios were also compared using an independent sample t-test. The blood level of methadone was not correlated with the clinical outcome of MMT with the moderate range of doses given. However, the retention of patients who had a free peak-to-trough ratio >2 was significantly poorer than those whose ratio was <2. Thus, monitoring plasma methadone levels is unlikely to be effective for guiding dosing decisions in situations where compliance with MMT is already very high or when the methadone dose is no longer the dominant factor in determining the clinical outcome. However, monitoring plasma methadone levels is still helpful for guiding the dosage for patients with a rapid metabolism.

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.

Effect of Methadone Dose on Maintenance Treatment and Health Consequences Among Heroin Addicts in South China

A retrospective cross-sectional study was conducted with a convenience sample of 197 adults receiving methadone maintenance treatment in Kunming city, South China, in 2010. The aim of the study was to determine the association of methadone maintenance dose on a variety of treatment outcomes. Treatment modalities, the adverse reactions to methadone treatment, the physical and mental outcomes of the treatment, and risk behavior changes were assessed. Multilevel negative and logistic binomial regression analyses were carried out, which demonstrated that methadone maintenance dose in this sample was not associated with improved treatment adherence or with quality of life. We concluded that dose had a small, if negligible, influence on the changes in adverse effects of methadone. Further research in dose differences between the genders should be conducted.

Accidental methadone ingestion in an infant: case report and review of the literature

INTRODUCTION

We discuss accidental methadone intoxication in an 11-month-old female infant, review the literature, and stress the potential for child abuse among methadone-maintained caregivers.

CASE

An 11-month-old female infant presented with lethargy. Vital signs were normal, and pupils were constricted. Sepsis workup revealed no evidence of bacterial infection. High venous pCO2 suggested respiratory acidosis. Urine toxicology revealed high concentrations of methadone and its metabolites, and the diagnosis of methadone intoxication was confirmed when 0.1 mg/kg intravenous naloxone normalized the child's behavior. Social service agency inquiries found that the child's grandfather had been prescribed methadone for acquired morphine addiction. He carried 5-mg methadone tablets in his pocket and had recently babysat the infant. The patient was subsequently discharged home with pediatric and community services follow-up.

DISCUSSION

Methadone intoxication should be considered in children presenting with lethargy, miosis, and respiratory depression. Seventy-two percent of reported methadone poisoning patients are symptomatic, and unintentional poisoning is a real danger to children because small amounts can be fatal. There are also several case reports where the cause of intoxication was homicide by the parents. Initial management consists of establishing an airway, and naloxone may be indicated, before urine toxicology results are obtained, to help establish the diagnosis. However, if 2 doses do not reverse the child's symptoms, the diagnosis should be questioned. When repeated bolus doses of naloxone are indicated, a continuous infusion may be preferable.

Role of CYP3A5 in Abnormal Clearance of Methadone

Objective:

To report a case of unusually low concentrations of methadone in a polydrug abuser during maintenance treatment with methadone.

Case Summary:

A 25-year-old man (weight 55 kg, height 165 cm) with a 12-year history of polydrug abuse was admitted to an opiates withdrawal methadone program. At the time of our observation, he was using both cannabinoids and heroin; no other medical conditions were discovered. Within the opiates withdrawal methadone program, under medical supervision, the patient started methadone therapy (20 mg/day). Two weeks later, an Abuscreen assay for methadone screening in the urine was negative and, to prevent the development of withdrawal symptoms, the dose of methadone was increased to 60 mg/day. One day later, the patient was asked to collect another urine sample in the presence of a nurse. The Abuscreen for methadone in urine remained negative. Evaluation of urinary samples collected over 24 hours documented low concentrations of methadone and high levels of 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (the primary metabolite of methadone). Evaluation for the presence of the most common polymorphisms in the cytochrome P450 and P-glycoprotein genes showed that the patient was heterozygous for the CYP3A531 allele and for 2 single nucleotide polymorphisms in the P-glycoprotein gene (1236C/T and 3435C/T).

Discussion:

In this patient, poor methadone adherence was ruled out because of the presence of physicians and nurses during both methadone maintenance treatment and Abuscreen screening. Moreover, because the patient reported only heroin and cannabis at the time of evaluation, drug interactions were ruled out as possible causes for the rapid clearance of methadone.

Conclusions:

In this case, CYP3A5 polymorphism may have played a role in the rapid methadone metabolism.

Concentrations of methadone in breast milk and plasma in the immediate perinatal period

This study evaluates concentrations of methadone in breast milk and plasma among a sample of methadone-maintained women in the immediate perinatal period. Twelve methadone-maintained, lactating women provided blood and breast milk specimens 1, 2, 3, and 4 days after delivery. Specimens were collected at the time of trough (just before methadone dose) and peak (3 hours after dosing) maternal methadone levels. Paired specimens of foremilk (prefeed) and hindmilk (postfeed) were obtained at each sampling time. Although there was a significant increase in methadone concentration in breast milk over time for the peak postfeed sampling time, t (22)=2.40, P=.0255, methadone concentrations in breast milk were small, ranging from 21 to 314 ng/mL, and were unrelated to maternal methadone dose. Results obtained from this study contribute to the recommendation of breastfeeding for methadone-maintained women regardless of methadone dose.

Methadone death, dosage and torsade de pointes: risk-benefit policy implications

Methadone maintenance treatment (MMT) for opioid dependency has consistently shown important heath, social and legal benefits. What started as a small experimental program in Lexington, Kentucky has grown and expanded substantially over 35 years. Its practice is now well established both in specialized centers and in the broader community. In society, methadone deaths represent an important issue of public safety: methadone diversion to and ingestion by nontolerant individuals outside of treatment. Within treatment, methadone deaths occur most commonly in the early stabilization period (due to issue of tolerance), in periods of transition, or among certain individuals who abuse other substances (opioids, benzodiazepines, or alcohol). Research suggests moderately high methadone dosages help improve patient retention. Results from pharmacodynamic, kinetic and stereospecific studies continue to support the importance of individualizing dose. For some patients, much larger doses may be necessary to fully achieve all pharmacotherapy goals of treatment. Practitioners must be cautious however as certain patients on higher dosages are predisposed to torsade de pointes and increased mortality. Policymakers have a responsibility in their decision-making to balance the quality of life benefits for patients within MMT with the risks of increased mortality both for individuals within treatment and the general public.

Correlation Between High Methadone Doses and Methadone Serum Levels in Methadone Maintenance Treatment (MMT) Patients

AIMS

To evaluate the relation between high methadone doses and methadone serum levels in MMT patients.

DESIGN

One hundred fifty-one steady methadone-dose patients were evaluated for methadone serum levels using GCMS. Urine samples during the month prior to the study-day were analysed and defined as positive if any sample was positive for any drug.

FINDINGS

Methadone dose correlated with methadone serum levels (Pearson R = 0.36, P < 0.0005). In 53 patients with no drug abuse, correlation was stronger (R = 0.53, P < 0.0005) than in 98 patients with any drug abuse (R = 0.25, P = 0.01).

CONCLUSIONS

We extended the well-established correlation between methadone doses and serum levels in patients receiving low or moderate (60 to 120 mg/day) to high methadone doses (up to 290 mg/day).

Population-based analysis of methadone distribution and metabolism using an age-dependent physiologically based pharmacokinetic model

Limited pharmacokinetic (PK) and pharmacodynamic (PD) data are available to use in methadone dosing recommendations in pediatric patients for either opioid abstinence or analgesia. Considering the extreme inter-individual variability of absorption and metabolism of methadone, population-based PK would be useful to provide insight into the relationship between dose, blood concentrations, and clinical effects of methadone. To address this need, an age-dependent physiologically based pharmacokinetic (PBPK) model has been constructed to systematically study methadone metabolism and PK. The model will facilitate the design of cost-effective studies that will evaluate methadone PK and PD relationships, and may be useful to guide methadone dosing in children. The PBPK model, which includes whole-body multi-organ distribution, plasma protein binding, metabolism, and clearance, is parameterized based on a database of pediatric PK parameters and data collected from clinical experiments. The model is further tailored and verified based on PK data from individual adults, then scaled appropriately to apply to children aged 0-24 months. Based on measured variability in CYP3A enzyme expression levels and plasma orosomucoid (ORM2) concentrations, a Monte-Carlo-based simulation of methadone kinetics in a pediatric population was performed. The simulation predicts extreme variability in plasma concentrations and clearance kinetics for methadone in the pediatric population, based on standard dosing protocols. In addition, it is shown that when doses are designed for individuals based on prior protein expression information, inter-individual variability in methadone kinetics may be greatly reduced.

Early impact of methadone induction for heroin dependence: differential effects of two dose sequences in a randomized controlled study

The pharmacodynamic and pharmacokinetic effects of 2 methadone (METH) induction dose sequences were evaluated in this 15-day outpatient experimental protocol. Heroin-dependent, non-treatment-seeking volunteers were randomly assigned (stratified for gender, race, and route of heroin use) to 2 groups. In 1 sequence, METH doses ascended (28, 56, then 84 mg/day; stepwise, n = 18), whereas in the other sequence doses escalated, then tapered (28-84 mg on Days 1-6 to 56 mg/day; rapid, n = 16). A contingency-management intervention was common to both groups. Drug use and heroin craving and opioid withdrawal symptoms decreased, whereas agonist symptoms and positive mood increased overall across days for both groups. Plasma concentrations and the acute reinforcing effects of METH paralleled each dose sequence. Stepwise relative to rapid METH induction significantly decreased heroin craving and opioid withdrawal symptoms and increased agonist symptoms and positive mood but did not significantly improve drug use or retention. Although these specific dosing procedures would not necessarily be used in clinical settings, they provide a procedural template that might be applied safely and effectively with a broader range of treatment-seeking individuals.

Therapeutic thresholds in methadone maintenance treatment: a receiver operating characteristic analysis

Twenty-four-hour trough (R)- and (R,S)-methadone plasma concentrations were measured on 94 methadone maintenance treatment (MMT) patients classified as 'responders' or 'non-responders', based on urine toxicology evidence of recent illicit opiate use. Receiver operating characteristic (ROC) curves for daily dose, dose/bodyweight, and (R)- and (R,S)-methadone trough plasma concentrations were used to identify optimal thresholds; areas under the curve (AUC) were used to compare predictive power. Non-responders (n=37) had a lower mean dose (73 mg/day versus 147 mg/day; p<0.001), (R)-methadone concentration (136 ng/ml versus 223 ng/ml; p<0.005) and (R,S)-methadone concentration (266 ng/ml versus 409 ng/ml; p=0.001) than responders. On multivariate regression, duration of treatment and methadone dose were significantly associated with treatment response. After backward stepwise regression, each year of treatment increased the odds of abstinence from illicit opioid use by 34% (OR 1.34; 95% CI 1.14-1.57)); each 20mg of methadone dose by 36% (OR 1.36 CI; 95% CI 1.11-1.67). On ROC analysis, AUC for daily dose (0.77, 95% CI 0.68-0.87), dose/bodyweight (0.76, 95% CI 0.66-0.85), (R)-methadone (0.73, 95% CI 0.63-0.84) and (R,S)-methadone concentration (0.70, 95% CI 0.59-0.81) did not differ significantly. Dose/bodyweight, and trough plasma concentrations of (R)- or (R,S)-methadone were no better predictors of treatment response than daily dose, and did not improve the fit of the model for treatment outcome as judged by the likelihood ratio test (p=0.21, 0.88, and 0.97, respectively). Optimal therapeutic thresholds (sensitivity, specificity) were: daily dose 100mg/day (67%, 81%); (R)-methadone 200 ng/ml (51%, 78%); (R,S)-methadone 400 ng/ml (40%, 81%). Thresholds with specificity near 90% (dose 140 mg/day; (R)-methadone 250 ng/ml; (R,S)-methadone 500 ng/ml) may help guide dose titration for patients continuing to use illicit opiates.

Opioid plasma concentrations in methadone-and buprenorphine-maintained patients

This is the first trial to compare the relationship of opioid plasma concentrations in methadone-versus buprenorphine-maintained subjects. Sixty subjects (19 females and 41 males) seeking treatment who met Diagnostic and Statistical Manual version IV (DSM-IV) criteria for opioid dependence were recruited and treated at the Drug Addiction Outpatient Clinic at the University of Vienna. Of these, 44 (11 female and 33 male) were included in the analyses of plasma concentrations. Subjects received either daily sublingual buprenorphine (2 mg or 8 mg tablets; maximum daily dose: 8 mg) or oral methadone (racemic R-/S-methadone) and were maintained on a stable dose after an induction period of 2 weeks. Mean dose and mean plasma concentrations were correlated on an individual and collective basis. Correlation was 0.51 for buprenorphine, whereas the score for methadone was 0.69. Intra-individual variation was much higher for buprenorphine (p<0.0001), while the concentration-to-dose ratio was very small. Based on the differences of the pharmacokinetics of blood plasma of the two agents, we tried to explain the differences in the acceptance of treatment, which was significantly lower in the buprenorphine-maintained group. No such differences could be evaluated between completers and dropouts in buprenorphine-maintained subjects, neither concerning withdrawal scores nor dose, plasma concentration, concentration-to-dose ratios or intra-individual variation.

The effects of methadone and its role in fatalities

Methadone is a synthetic opioid, used both as an analgesic in severe pain relief and now mainly in the treatment of opiate dependence. Such use of the drug has increased as its advantages have become widely recognized. There are undesirable outcomes from its greater use, including a substantial market in diverted methadone and a high number of deaths where the drug has been implicated. It is important to understand how and why methadone causes death so that such fatalities can be minimized, and to disseminate such information. This paper presents an overview of the chief effects of methadone on the human body, considering its metabolism, drug interactions and tolerance. The principal mechanisms by which methadone causes death are discussed: respiratory depression, aspiration of vomit, pulmonary oedema, bronchopneumonia, cardiac problems and renal failure. Many such deaths are preventable, if drug interactions and polydrug use are avoided, its longer period of metabolism and individuals' tolerance levels are considered. It is hoped that this paper will (a) help guide health professionals in their management and treatment of patients participating in methadone treatment programmes, and (b) provide some basic information for those dealing with individuals who have consumed methadone.

Dosage regimes in the prescription of heroin and other narcotics to chronic opioid addicts in Switzerland--Swiss national cohort study

AIMS

Within the guidelines of the research programme on medical prescription of narcotics for opioid addicts (PROVE), heroin, morphine, and methadone were prescribed to heavily opioid addicted individuals in Switzerland since 1994. This contribution analyses the course of dose levels during the treatment period.

DESIGN

Naturalistic description of consumed dosages per day and month.

SETTING AND PARTICIPANTS

The study describes the dosages prescribed to all individuals who began outpatient treatment in the PROVE programme in Switzerland between 1994 and 1996.

MEASUREMENTS

Consumed amount of narcotics per day and the course of dosage of injectable heroin in different treatment regimes.

FINDINGS

Heroin was the most frequently prescribed narcotic. Of all consumption days, heroin had been applied in 77% as injection and in 9% in a smokeable form. The mean daily dosage was 474 mg for intravenous application and 993 mg for the smokeable form. Second most frequent was the prescription of oral methadone, in most cases in combination with heroin. The mean amount of daily consumption of oral methadone was 53 mg. There were dosage differences between treatment regimes. During the course of treatment the mean dosage for injectable heroin per day decreased significantly and, depending on the treatment regime, almost linearly.

CONCLUSIONS

The significance of heroin dosages in heroin-assisted therapy for treatment outcome should be further explored, especially in the light of the markedly higher dosages in Switzerland compared to the UK. During the treatment period, dosages did not increase but generally decreased, indicating no further increase in tolerance.

Interindividual variability of the clinical pharmacokinetics of methadone: implications for the treatment of opioid dependence

Methadone is widely used for the treatment of opioid dependence. Although in most countries the drug is administered as a racemic mixture of (R)- and (S)- methadone, (R)-methadone accounts for most, if not all, of the opioid effects. Methadone can be detected in the blood 15-45 minutes after oral administration, with peak plasma concentration at 2.5-4 hours. Methadone has a mean bioavailability of around 75% (range 36-100%). Methadone is highly bound to plasma proteins, in particular to alpha(1)-acid glycoprotein. Its mean free fraction is around 13%, with a 4-fold interindividual variation. Its volume of distribution is about 4 L/kg (range 2-13 L/kg). The elimination of methadone is mediated by biotransformation, followed by renal and faecal excretion. Total body clearance is about 0.095 L/min, with wide interindividual variation (range 0.02-2 L/min). Plasma concentrations of methadone decrease in a biexponential manner, with a mean value of around 22 hours (range 5-130 hours) for elimination half-life. For the active (R)-enantiomer, mean values of around 40 hours have been determined. Cytochrome P450 (CYP) 3A4 and to a lesser extent 2D6 are probably the main isoforms involved in methadone metabolism. Rifampicin (rifampin), phenobarbital, phenytoin, carbamazepine, nevirapine, and efavirenz decrease methadone blood concentrations, probably by induction of CYP3A4 activity, which can result in severe withdrawal symptoms. Inhibitors of CYP3A4, such as fluconazole, and of CYP2D6, such as paroxetine, increase methadone blood concentrations. There is an up to 17-fold interindividual variation of methadone blood concentration for a given dosage, and interindividual variability of CYP enzymes accounts for a large part of this variation. Since methadone probably also displays large interindividual variability in its pharmacodynamics, methadone treatment must be individually adapted to each patient. Because of the high morbidity and mortality associated with opioid dependence, it is of major importance that methadone is used at an effective dosage in maintenance treatment: at least 60 mg/day, but typically 80-100 mg/day. Recent studies also show that a subset of patients might benefit from methadone dosages larger than 100 mg/day, many of them because of high clearance. In clinical management, medical evaluation of objective signs and subjective symptoms is sufficient for dosage titration in most patients. However, therapeutic drug monitoring can be useful in particular situations. In the case of non-response trough plasma concentrations of 400 microg/L for (R,S)-methadone or 250 microg/L for (R)-methadone might be used as target values.

Nucleus accumbens shell and core dopamine: differential role in behavior and addiction

Drug addiction can be conceptualized as a disturbance of behavior motivated by drug-conditioned incentives. This abnormality has been explained by Incentive-Sensitization and Allostatic-Counteradaptive theories as the result of non-associative mechanisms acting at the stage of the expression of incentive motivation and responding for drug reinforcement. Each one of these theories, however, does not account per se for two basic properties of the motivational disturbance of drug addiction: (1). focussing on drug- at the expenses of non-drug-incentives; (2). virtual irreversibility. To account for the above aspects we have proposed an associative learning hypothesis. According to this hypothesis the basic disturbance of drug addiction takes place at the stage of acquisition of motivation and in particular of Pavlovian incentive learning. Drugs share with non-drug rewards the property of stimulating dopamine (DA) transmission in the nucleus accumbens shell but this effect does not undergo habituation upon repeated drug exposure, as instead is the case of non-drug rewards. Repetitive, non-decremental stimulation of DA transmission by drugs in the nucleus accumbens septi (NAc) shell abnormally strengthens stimulus-drug associations. Thus, stimuli contingent upon drug reward acquire powerful incentive properties after a relatively limited number of predictive associations with the drug and become particularly resistant to extinction. Non-contingent occurrence of drug-conditioned incentive cues or contexts strongly facilitates and eventually reinstates drug self-administration. Repeated drug exposure also induces a process of sensitization of drug-induced stimulation of DA transmission in the NAc core. The precise significance of this adaptive change for the mechanism of drug addiction is unclear given the complexity and uncertainties surrounding the role of NAc core DA in responding but might be more directly related to instrumental performance.

Toxicologic aspects of heroin substitution treatment

Heroin abuse is an international problem with which all countries must continually cope. Many countries have implemented heroin substitution therapy as an effective means of decreasing illicit heroin use, crime, HIV risk, and death, and in improving employment and social adjustment. Although methadone is the most commonly used medication for heroin substitution, other agonists in current use include levomethadyl acetate (LAAM), buprenorphine, and pharmaceutical-grade heroin. This report reviews toxicologic issues that arise in these programs. A broad array of testing methodologies are available that allow selection of on-site testing or laboratory-based methodology. Urine specimens may be monitored for nonprescribed drugs on a qualitative or semiquantitative basis. Methods for differentiating opiate sources by urinalysis have been proposed to distinguish poppy seed consumption from heroin abuse and for distinguishing pharmaceutical-grade heroin from illicit heroin. Therapeutic drug monitoring for methadone in plasma continues to be evaluated for use in establishing adequate dosing and detecting diversion, and new methods have been devised for measurement of the optical isomers of methadone in plasma. Biologic specimens, in addition to plasma and urine, have been evaluated for use in drug monitoring, including sweat, hair, and oral fluid, with promising results. Overall, the many recent developments in testing methodology provide more effective means to assess patients in heroin substitution programs and should contribute to improvements in public health.

Therapeutic drug monitoring in methadone maintenance: choosing a matrix

Methadone maintenance is the premier pharmacological treatment for opioid addiction, but it is rarely informed by evidence-based practice guidelines for dosage monitoring and adjustment. Such guidelines are crucial because the pharmacokinetics of methadone vary greatly among patients, and this variation may account for differences in treatment outcome. We review the pharmacokinetics of methadone and factors that may alter it (including drug interactions, disease states, and idiosyncratic differences among patients). Also reviewed are prospects for therapeutic drug monitoring (TDM) of methadone in plasma, urine, sweat, and saliva. Due to its ease of collection and its presumed representation of the bioavailable free-fraction of methadone, saliva may be a promising matrix. However, saliva methadone concentrations are influenced by salivary pH, and future studies are needed to determine how to control for that. Administrative, medical, and social implications of methadone TDM are briefly discussed.

Plasma concentrations of the enantiomers of methadone and therapeutic response in methadone maintenance treatment

Methadone is a 50:50 mixture of two enantiomers and (R)-methadone accounts for the majority of its opioid effect. The aim of this study was to determine whether a blood concentration of (R)-methadone can be associated with therapeutic response in addict patients in methadone maintenance treatment. Trough plasma concentrations of (R)-, (S)- and (R,S)-methadone were measured in 180 patients in maintenance treatment. Therapeutic response was defined by the absence of illicit opiate or cocaine in urine samples collected during a 2-month period prior to blood sampling. A large interindividual variability of (R)-methadone concentration-to-dose-to-weight ratios was found (mean, S.D., median, range: 112, 54, 100, 19-316 ng x kg/ml x mg). With regard to the consumption of illicit opiate (but not of cocaine), a therapeutic response was associated with (R)- (at 250 ng/ml) and (R,S)-methadone (at 400 ng/ml) but not with (S)-methadone concentrations. A higher specificity was calculated for (R)- than for (R,S)-methadone, as the number of non-responders above this threshold divided by the total number of non-responders was higher for (R,S)-methadone (19%) than for (R)-methadone (7%). The results support the use of therapeutic drug monitoring of (R)-methadone in cases of continued intake of illicit opiates. Due to the variability of methadone concentration-to-dose-to-weight ratios, theoretical doses of racemic methadone could be as small as 55 mg/day and as large as 921 mg/day to produce a plasma (R)-methadone concentration of 250 ng/ml in a 70-kg patient. This demonstrates the importance of individualizing methadone treatment.

Methadone deaths: a toxicological analysis

AIMS

To perform a toxicological analysis of deaths involving methadone and to determine the fatal concentration of methadone in such deaths.

METHODS

Deaths in which methadone was mentioned in the cause of death were identified. Deaths were divided into those associated with methadone only and deaths in which the cause of death was a combination of methadone and other drugs. Toxicological findings in these deaths were analysed and compared with previously published data.

RESULTS

One hundred and eleven cases were analysed. In 55 cases, methadone poisoning was given as the sole cause of death. Fifty victims were adults, age range 17-51 years (median, 23), with five victims under 14 years of age. The mean methadone concentration in the adult deaths was 584 micrograms/litre (median, 435; range, 84-2700). In 56 cases, age range 15-49 years, (median, 28), death was ascribed to a combination of methadone and other drugs. The mean methadone concentration in these deaths was 576 micrograms/litre (median, 294; range, 49-2440). In 26 cases, multiple site sampling was performed. This revealed that there could be a 100% discrepancy between methadone concentrations, and other drugs, in samples collected in different sites in the same body.

CONCLUSIONS

There is an overlap between quoted therapeutic methadone concentrations and methadone concentrations seen in fatalities. However, those dying from methadone poisoning might not be the same as those in a methadone programme. A degree of caution must be exercised in determining a fatal concentration because of the phenomenon of postmortem redistribution. Pathologists and toxicologists need to examine all the available postmortem findings in identifying the cause of death.

A therapeutic use of the methadone fluvoxamine drug interaction

BACKGROUND

Methadone has been effectively used in the treatment of opiate dependence. Adequate dose and blood level have correlated with success in treatment. A number of factors including the regular use of alcohol, medications, and urinary pH can influence blood level and thereby effectiveness. Fluvoxamine has been shown to increase methadone blood levels.

METHODS

Single case report.

RESULTS

A patient unable to maintain an effective methadone blood level despite a dose of 200 mg per day was administered fluvoxamine with subsequent increase in her methadone blood level and reduction of opiate withdrawal symptoms.

CONCLUSIONS

In patients unable to maintain an effective methadone blood level throughout the dosing interval, fluvoxamine can help increase the methadone blood level and alleviate opiate withdrawal symptoms.

Craving patterns in methadone maintenance treatment with dextromoramide as adjuvant

A study was performed to establish the effect on opiate craving among six long-term opiate-dependent subjects in methadone maintenance treatment. Subjects currently stabilised on methadone, received 5 or 10 mg dextromoramide besides methadone. During the study the usual methadone dose was diminished according to the individual subject's expectation of the effect of dextromoramide addition. A clear drug-effect relationship between the increment of dextromoramide plasma concentration and decrement of opiate craving could be seen. A craving increase before drug administration was seen in three cases. The results could imply beneficial effects of a short-acting opiate on diminishing craving in opiate addicts who are difficult to stabilise with methadone maintenance treatment.

Development of validated stereoselective methods for methadone determination in clinical samples

A stereoselective analysis of methadone (Mtd) in whole blood and serum was developed using liquid chromatography on a protein based chiral stationary phase. Liquid-liquid extraction (LLE) and solid phase extraction methods were applied before chromatographic analysis. The extraction procedure, as well as the choice of the biological matrix, showed significant differences in the extraction yield and in the precision of the assays. Serum was selected for this assay and LLE was chosen as the preparation step because of its simplicity and rapidity. The total procedure was validated and applied to clinical samples. Samples taken from 45 heroin-addicted patients were analyzed. A correlation was found between the dose administered and Mtd concentration (total and R-form), but interindividual variability of the total normalized Mtd was seen (concentration varied from 90 to 530 ng/ml). Furthermore, two populations were apparently observed with a mean Mtd concentration of 200 and 475 ng/ml, respectively. Stereoselective analyses showed that more than 50% of the patients presented a nonracemic ratio, and particularly about 25% showed a preferential metabolism of the active R-Mtd enantiomer. Therefore, the stereoselective determination of Mtd is necessary to improve the quality of the treatment of heroin addiction.

Population pharmacokinetics of methadone in opiate users: characterization of time-dependent changes

AIMS

Although methadone is widely used to treat opiate dependence, guidelines for its dosage are poorly defined. There is increasing evidence to suggest that a strategy based on plasma drug monitoring may be useful to detect non-compliance. Therefore, we have developed a population-based pharmacokinetic (POP-PK) model that characterises adaptive changes in methadone kinetics.

METHODS

Sparse plasma rac-methadone concentrations measured in 35 opiate-users were assessed using the P-Pharm software. The final structural model comprised a biexponential function with first-order input and allowance for time-dependent change in both clearance (CL) and initial volume of distribution (V ). Values of these parameters were allowed to increase or decrease exponentially to an asymptotic value.

RESULTS

Increase in individual values of CL and increase or decrease in individual values of V with time was observed in applying the model to the experimental data.

CONCLUSIONS

A time-dependent increase in the clearance of methadone is consistent with auto-induction of CYP3A4, the enzyme responsible for much of the metabolism of the drug. The changes in V with time might reflect both up- and down-regulation of alpha1-acid glycoprotein, the major plasma binding site for methadone. By accounting for adaptive kinetic changes, the POP-PK model provides an improved basis for forecasting plasma methadone concentrations to predict and adjust dosage of the drug and to monitor compliance in opiate-users on maintenance treatment.

Drug addiction as dopamine-dependent associative learning disorder

Natural rewards preferentially stimulate dopamine transmission in the nucleus accumbens shell. This effect undergoes adaptive changes (one-trial habituation, inhibition by appetitive stimuli) that are consistent with a role of nucleus accumbens shell dopamine in associative reward-related learning. Experimental studies with a variety of paradigms confirm this role. A role in associative stimulus-reward learning can provide an explanation for the extinction-like impairment of primary reinforcement that led Wise to propose the 'anhedonia hypothesis'. Addictive drugs share with natural rewards the property of stimulating dopamine transmission preferentially in the nucleus accumbens shell. This response, however, in contrast to that to natural rewards, is not subjected to one-trial habituation. Resistance to habituation allows drugs to activate dopamine transmission in the shell non-decrementally upon repeated self-administration. It is hypothesized that this process abnormally strengthens stimulus-drug associations thus resulting in the attribution of excessive motivational value to discrete stimuli or contexts predictive of drug availability. Addiction is therefore the expression of the excessive control over behaviour acquired by drug-related stimuli as a result of abnormal associative learning following repeated stimulation of dopamine transmission in the nucleus accumbens shell.

Optimizing response to methadone maintenance treatment: use of higher-dose methadone

Using signs, symptoms and serum methadone levels to guide evaluation, the authors treated 164 patients in a methadone maintenance program with doses of methadone exceeding 100 mg/d. The mean dose of these higher dose (HD) patients was 211 mg/d (range 110-780 mg/d). A comparison group (C) of 101 patients was randomly selected from the general clinic population (mean dose 65 mg/d). At intake the HD group reported $153/day of heroin use versus $87/day in the C group. The HD group had more patients whose opiate of choice was an oral pharmaceutical (30% versus 2% of the C group). Sixty-three percent of the HD group had comorbid Axis I psychiatric diagnoses compared to 32% of the C group. Response to psychopharmacologic treatment was enhanced by increased methadone dose in HD patients with "refractory" psychiatric disorders. Urine toxicologies described as "before" were collected prior to increase over 100 mg/d in the HD group or at the first routine urine toxicology collection of the calendar year for the C group. These results were compared to the most recent urine toxicologies for both groups ("after"). The percentage of toxicologies positive for illicit drugs in the HD group dropped from 87% "before" to 3% "after". The C group were 54% positive "before" and 37% positive "after". We conclude that doses of methadone in excess of 100 mg/d (range 110-780 mg/d in our sample of 164 patients) are not only safe but necessary to prevent illicit opiate use, stabilize psychiatric symptoms, and diminish abuse of alcohol and benzodiazepines in many patients.

Induction of antibodies to methadone during methadone maintenance treatment of heroin addicts and its possible clinical implications

By means of two different types of enzyme-linked immunosorbent assay (ELISA) techniques, antibodies to methadone were detected in blood plasma of heroin addicts on methadone maintenance treatment. In 11-15% of cases immunoglobulin (Ig) M antibodies were detected, while IgG antibodies were observed in 33-40%. At least two types of antibodies to methadone were induced-antibodies with high affinity to methadone and low-affinity antibodies more specific for morphine than for methadone. The methadone antibody-positive group of patients had a significantly higher plasma methadone concentration--440 ng/ml, than the antibody-negative group--250 ng/ml (P < 0.005) despite almost the same mean therapeutic doses of methadone. Of patients with all types of antibodies to methadone 52% were human immunodeficiency virus (HIV)-positive, whereas in the group without antibodies, HIV-positive reactions were observed in 10.5% only (P < 0.002). Alternatively, 87.5% of HIV-positive patients had antibodies to methadone, a fact which should be taken into consideration during methadone dose adjustment.

Therapeutic drug monitoring for methadone: scanning the horizon

The initial assessment and subsequent monitoring of compliance in methadone treatment programmes are excessively reliant on the accuracy of self-report from opiate addicts themselves. Given the central position of methadone treatment in the therapeutic options currently available and with the increasing number of opiate addicts requiring treatment, improved methods of judging optimal methadone treatment are required. This paper explores the possible future options for assessing the adequacy of methadone prescribing from the analysis of methadone levels in urine, blood, hair and saliva. The particular promise of plasma therapeutic drug monitoring for methadone is explored, accompanied by an account of the state of the art at the time of writing.

Plasma methadone concentrations as an indicator of opioid withdrawal symptoms and heroin use in a methadone maintenance program

Plasma methadone concentrations and its main metabolite D,L-2-ethylidiene-1,5-dimethyl-3,5-diphenylpyrrolidine (EDDP) were determined in 93 patients under methadone maintenance treatment to assess their relationship with heroin use and opioid withdrawal symptoms. Neither plasma concentrations of methadone nor EDDP were significantly different when patients that used heroin in last 3 months were compared with those testing negative for this drug (methadone, 355 +/- 217 versus 369 +/- 216 ng/ml, t = 0.29, P = NS; EDDP, 49 +/- 28 versus 54 +/- 40 ng/ml, t = 0.51, P = NS). No correlation between opioid withdrawal scale scores and plasma concentrations of methadone (r = 0.02, P = NS) and EDDP (r = -0.14, P = NS) was found. Therapeutic drug monitoring during methadone maintenance seems to be useful for assessing compliance with treatment but not for predicting heroin use and subjective withdrawal symptoms.

A motivational learning hypothesis of the role of mesolimbic dopamine in compulsive drug use

The effects of drugs and substances of abuse on central dopamine (DA) transmission studied by in vivo monitoring techniques have been examined and compared with those of conventional reinforcers and in particular with food. The similarities and differences in the action of drugs and conventional reinforcers on DA transmission can provide the basis for an hypothesis of the mechanism of drug addiction and compulsive drug use. This hypothesis states that drug addiction is due to excessive control over behaviour exerted by drug-related stimuli as a result of abnormal motivational learning induced by repeated drug exposure. Such abnormal motivational learning would derive from the repetitive non-habituating property of drugs of abuse to activate DA transmission phasically in the nucleus accumbens (NAc) 'shell'. Thus, activation of DA transmission by conventional reinforcers is under strong inhibitory control by previous exposure to the reinforcer (habituation); this, however, is not the case with drug reinforcers. Repetitive, non-adaptive release of DA in the NAc 'shell' by drugs of abuse would result in abnormal strengthening of stimulus-reward (incentive learning) and stimulus-response associations (habit learning) that constitute the basis for craving and compulsive drug use.

Influence of plasma-protein binding on analgesic effect of methadone in rats with spontaneous withdrawal

The effect of spontaneous withdrawal on alpha 1-acid glycoprotein (AAG) levels and methadone protein binding has been studied in the rat. Animals were made physically dependent on morphine by providing morphine HCl in drinking water for three weeks. The natural opiate withdrawal was induced in rats by substituting the morphine solution with drinking water. The severity of the abstinence syndrome was assessed at various time intervals. After 12 h of withdrawal, the animals showing abstinence signs and low morphine levels were injected with intravenous methadone (0.35 mg kg-1) and the analgesic effect was measured by the tail-flick method and compared with animals receiving water. The oral administration of morphine produced an increase in AAG levels from 0.64 +/- 0.05 g L-1 in control animals to 1.47 +/- 0.92 g L-1 in experimental animals at the point of withdrawal and 1.21 +/- 0.09 g L-1 24 h after withdrawal. The percentage of methadone unbound was significantly lower in morphine-treated than in control animals. A significant correlation between AAG levels and percentage of methadone bound was observed. A parallel analgesic effect after intravenous methadone, as measured by AUC in the tail-flick test, was less in abstinence animals than in control (287.6 +/- 24.8 compared with 401.0 +/- 37.06s min). We suggest that in the withdrawal syndrome an adjustment of methadone dose may be necessary because of changes in protein binding.

Craving despite extremely high methadone dosage

A clinical case study is presented of an opiate addict, currently under methadone maintenance treatment (MMT), who claims the need of a higher daily methadone dose. He is admitted to a closed metabolic ward, where he receives 250 mg methadone per day. During 24 h both pharmacokinetic parameters and craving levels are measured simultaneously. Results show extremely high methadone concentrations and its primary metabolite EDDP in plasma and urine. The craving level shows a distinguished peak around the methadone administration on both measured days. Withdrawal symptoms as well as self-reported craving did not correspond at all to the extremely high methadone concentration level in plasma. So we suggest that in individual cases if high methadone doses and plasma methadone levels are not able to diminish craving symptoms, dose adjustment should be accompanied by education regarding daily anticipatory increase of opiate craving.

Subjective and objective symptoms in relation to plasma methadone concentration in methadone patients

Two rating scales, which were originally developed for measurements of objective and subjective signs of opiate withdrawal, were used to evaluate potential estimates (correlates) of methadone effects in relation to plasma methadone concentrations. Patients participating in our regular methadone maintenance treatment project were studied during 24 h after the intake of the daily methadone dose. Methadone concentrations in plasma were compared to the subjective (estimated by the patients) and objective (estimated by the investigator) signs of the drug effects before, and 2.5, 5, 9 and 24 h after intake of methadone. Some new items possibly related to rising methadone concentrations were added to the subjective scale. Results indicated that, for subjective ratings, the majority of the items investigated corresponded well with the plasma methadone concentrations. The most significant associations were found for the following items: low psychomotor speed, alertness, running nose, yawning and anxiety. For objective ratings, only the items rhinorrhea, piloerection and signs of anxiety were significantly associated with the methadone concentrations. These rating scales may, together with plasma methadone determinations, be of considerable value when making dose adjustments for methadone maintenance patients. Further work is, however, needed to establish concentration-effect relationships.

Methadone maintenance treatment: an update

Available data (this review includes old major articles and recent articles) show that, although results are heterogeneous, methadone maintenance treatments (MMTs) have a real efficiency not only to reduce illicit opiate abuse (50-80% of patients under MMT did not use heroin in the preceding month) but also to reduce criminality, HIV risks and mortality, and to improve social rehabilitation, without inducing other alternative substance abuse. A minority of patients (perhaps 5-20%) stay on MMT on a very long-term basis (more than 10 years). Efficiency of MMTs are rather poorly related to patients' variables, with the exception of a moderately deleterious effect of a low age at onset of opiate dependence, a precocious or high involvement in criminality and an abuse of non-opiate drugs. On the other hand, variables related to treatment play a more important role in explaining heterogeneity of results. Optimal daily dose, high quality of medical and psycho-social services, clear orientation towards social rehabilitation and treatment retention (to allow a sufficient duration of treatment) and slow detoxification regimen of well-stabilized patients are all factors contributing to better results.