The successful use of parenteral methadone in a patient with a prolonged QTc interval

Recent case reports have raised concerns about the potential for methadone to prolong the QTc interval (QT corrected for heart rate) and predispose patients to torsade de pointes (TdP), a life-threatening arrhythmia. We present a case report that describes the successful use of parenteral and oral methadone in a patient with uncontrolled cancer pain and a history of QTc prolongation. We describe an approach to the use of methadone in this patient and review both case reports and recent prospective studies that have evaluated the risk of TdP and the long-term outcome with respect to the development of TdP in patients receiving methadone for chronic pain or addiction.

Cerebral metabolism and mood in remitted opiate dependence

BACKGROUND

Opiate-dependent individuals are prone to dysphoria that may contribute to treatment failure. Methadone-maintenance therapy (MMT) may mitigate this vulnerability, but controversy surrounds its long-term use. Little is known about the neurobiology of mood dysregulation in individuals receiving or removed from MMT.

METHODS

Fifteen opiate-abstinent and 12 methadone-maintained, opiate-dependent subjects, who lacked other Axis I pathology, and 13 control subjects were compared on the Cornell Dysthymia Rating Scale (CDRS) and regional cerebral glucose metabolism (rCMRglc) using [(18)F]fluorodeoxyglucose positron emission tomography.

RESULTS

CDRS scores showed no group differences. Opiate-abstinent subjects had lower rCMRglc than control subjects in the bilateral perigenual anterior cingulate cortex (ACC), left mid-cingulate cortex, left insula and right superior frontal cortex. Methadone-maintained subjects exhibited lower rCMRglc than control subjects in the left insula and thalamus. In opiate-abstinent subjects, rCMRglc in the left perigenual ACC and mid-cingulate cortex correlated positively with CDRS scores.

CONCLUSIONS

In remitted heroin dependence, opiate-abstinence is associated with more widespread patterns of abnormal cortical activity than MMT. Aberrant mood processing in the left perigenual ACC and mid-cingulate cortex, seen in opiate-abstinent individuals, is absent in those receiving MMT, suggesting that methadone may improve mood regulation in this population.

Full participation in harm reduction programmes is associated with decreased risk for human immunodeficiency virus and hepatitis C virus: evidence from the Amsterdam Cohort Studies among drug users

OBJECTIVES

To investigate the impact of harm-reduction programmes on HIV and hepatitis C virus (HCV) incidence among ever-injecting drug users (DU) from the Amsterdam Cohort Studies (ACS).

METHODS

The association between use of harm reduction and seroconversion for human immunodeficiency virus (HIV) and/or hepatitis C virus (HCV) was evaluated using Poisson regression. A total of 714 DU were at risk for HIV and/or HCV during follow-up. Harm reduction was measured by combining its two most important components--methadone dose and needle exchange programme (NEP) use--and looking at five categories of participation, ranging from no participation (no methadone in the past 6 months, injecting drug use in the past 6 months and no use of NEP) to full participation (> or = 60 mg methadone/day and no current injecting or > or = 60 mg methadone/day and current injecting but all needles exchanged).

RESULTS

Methadone dose or NEP use alone were not associated significantly with HIV or HCV seroconversion. However, with combination of these variables and after correction for possibly confounding variables, we found that full participation in a harm reduction programme (HRP) was associated with a lower risk of HIV and HCV infection in ever-injecting drug users (DU), compared to no participation [incidence rate ratio 0.43 (95% CI 0.21-0.87) and 0.36 (95% CI 0.13-1.03), respectively].

CONCLUSIONS

In conclusion, we found that full participation in HRP was associated with a lower incidence of HCV and HIV infection in ever-injecting DU, indicating that combined prevention measures--but not the use of NEP or methadone alone--might contribute to the reduction of the spread of these infections.

Intimate partner violence and HIV risks: a longitudinal study of men on methadone

Whereas research has suggested that drug-involved men are at disproportionately high risk of engaging in transmission risk behaviors for HIV and of perpetrating intimate partner violence (IPV) against women, only a few cross-sectional studies have examined the relationship between IPV and HIV/sexually transmitted infection (STI) transmission risks among heterosexual, drug-involved men. This study builds on previous cross-sectional research by using a longitudinal design to examine the temporal relationships between perpetration of IPV and different HIV/STI transmission risks among a random sample of 356 men on methadone assessed at baseline (wave 1), 6 months (wave 2), and 12 months (wave 3). The findings indicate that (1) perpetration of IPV in the past 6 months at wave 1 was associated with having more than one intimate partner, buying sex, and sexual coercion at subsequent waves and that (2) non-condom use, injecting drugs, and sexual coercion at wave 1 were associated with subsequent IPV. The temporal relationships between perpetration of IPV and HIV risks found in this study underscore the need for HIV prevention interventions targeting men on methadone to consider IPV and HIV risks as co-occurring problems.

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.

Comparing adaptive stepped care and monetary-based voucher interventions for opioid dependence

This 6-month randomized clinical trial (with 3-month follow-up) used a 2x2 design to compare the independent and combined effectiveness of two interventions designed to improve outcomes in treatment-seeking opioid dependent patients (n=236): motivated stepped care (MSC) and contingent voucher incentives (CVI). MSC is an adaptive treatment strategy that uses principles of negative reinforcement and avoidance to motivate both attendance to varying levels of counseling services and brief periods of abstinence [Brooner, R.K., Kidorf, M., 2002. Using behavioral reinforcement to improve methadone treatment participation. Sci. Pract. Perspect. 1, 38-46; Brooner, R.K., Kidorf, M.S., King, V.L., Peirce, J.M., Bigelow, G.E., Kolodner, K., 2004. A modified "stepped care" approach to improve attendance behavior in treatment seeking opioid abusers. J. Subst. Abuse Treat. 27, 223-232]. In contrast, CVI [Higgins, S., Delaney, D.D., Budney, A.J., Bickel, W.K., Hughes, J.R., Foerg, B.A., Fenwick, J.W., 1991. A behavioral approach to achieving initial cocaine abstinence. Am. Psychiatr. 148, 1218-1224] relies on positive reinforcement to motivate drug abstinence. The results showed that the combined approach (MSC+CVI) was associated with the highest proportion of drug-negative urine samples during both the randomized and 3-month follow-up arms of the evaluation. The CVI-only and the MSC-only conditions evidenced similar proportions of drug-negative urine samples that were both significantly greater than the standard care (SC) comparison group. Voucher-based reinforcement was associated with better retention, while adaptive stepped-based care was associated with better adherence to scheduled counseling sessions. These results suggest that both CVI and MSC are more effective than routine care for reducing drug use in opioid dependent outpatients, and that the overall benefits of MSC are enhanced further by adding positive reinforcement.

Norman Cousins Lecture. Glia as the "bad guys": implications for improving clinical pain control and the clinical utility of opioids

Within the past decade, there has been increasing recognition that glia are far more than simply "housekeepers" for neurons. This review explores two recently recognized roles of glia (microglia and astrocytes) in: (a) creating and maintaining enhanced pain states such as neuropathic pain, and (b) compromising the efficacy of morphine and other opioids for pain control. While glia have little-to-no role in pain under basal conditions, pain is amplified when glia become activated, inducing the release of proinflammatory products, especially proinflammatory cytokines. How glia are triggered to become activated is a key issue, and appears to involve a number of neuron-to-glia signals including neuronal chemokines, neurotransmitters, and substances released by damaged, dying and dead neurons. In addition, glia become increasingly activated in response to repeated administration of opioids. Products of activated glia increase neuronal excitability via numerous mechanisms, including direct receptor-mediated actions, upregulation of excitatory amino acid receptor function, downregulation of GABA receptor function, and so on. These downstream effects of glial activation amplify pain, suppress acute opioid analgesia, contribute to the apparent loss of opioid analgesia upon repeated opioid administration (tolerance), and contribute to the development of opioid dependence. The potential implications of such glial regulation of pain and opioid actions are vast, suggestive that targeting glia and their proinflammatory products may provide a novel and effective therapy for controlling clinical pain syndromes and increasing the clinical utility of analgesic drugs.

[Treatment retention and evolution of clientele in a low threshold methadone substitution treatment program in Montreal]

OBJECTIVES

To evaluate client treatment retention and evolution in terms of living conditions, at-risk behaviours, and the use of psychoactive substances (PAS) over a one-year period, following admission into a low-threshold methadone program in Montreal.

METHOD

Individual interviews were administered to 114 clients from Relais-Méthadone (RM) at admission and one year after treatment initiation. Participants reported on PAS consumption and unsafe practices of drug use and sexual behaviours at high risk for transmission of HIV, sexually transmitted infections (STI) and other blood-borne viruses (BBV). Services utilized by clients were documented from Relais-Méthadone files. Bivariate analyses were used to compare data recorded at admission and one-year follow-up.

RESULTS

The treatment retention rate after one year at RM was 64%. However, by taking into account those clients who were transferred to a regular program during the study period, as well as those who voluntarily tapered their methadone treatment (16.7%), the status of 80.7% of clients demonstrated improvement one year after admission into treatment. Furthermore, the clients who remained in treatment for a year for whom information was available (n = 60) showed a tendency towards more stable living conditions. They also demonstrated a significant decrease in both the number of PAS injections and in risky behaviours related to drug consumption. A statistically significant decrease in the frequency of heroine and cocaine use was also observed. By contrast, however, two thirds of the individuals in treatment after a year (n = 42) maintained or increased their daily consumption of other PAS.

DISCUSSION

The treatment retention rate is comparable to other low or regular threshold substitution programs. The results support previous studies showing that the methadone substitution treatment reduces heroine and cocaine consumption, and decreases the number of unsafe behaviours that could potentially transmit HIV, STI and BBV for the majority of clients who remained in treatment. Future research could focus attention on people who abandon treatment and those who present at-risk behaviours during treatment.

A twist on torsade: a prolonged QT interval on methadone

A woman developed a prolonged QT interval and torsade de pointes while on methadone treatment for heroin addiction. We think methadone, or its impaired metabolism, was the major cause for her prolonged QT interval and progression to torsade. However, torsade is often multifactorial, as was likely so in this case. We advise physicians treating patients taking methadone to obtain careful medication and drug-use histories, screen for risk factors associated with long QT syndrome, counsel patients about potential drug interactions, and measure the QT interval before and during methadone treatment in high-risk patients.

Differences in orbitofrontal activation during decision-making between methadone-maintained opiate users, heroin users and healthy volunteers

OBJECTIVE

Previously, we reported that opiate users enrolled in methadone treatment made 'risky' choices on a decision-making task following a loss of points compared with heroin users and healthy volunteers. One possible explanation for this behaviour is that methadone users were less sensitive to punishment on immediately preceding unsuccessful trials.

METHODS

We sought to explore this finding from a neural perspective by performing a post hoc analysis of data from a previous [see text] positron emission tomography study. We restricted the analysis to the opiate groups and controls, assessing differences between opiate users on methadone and those on heroin.

RESULTS

We found significant over-activation in the lateral orbitofrontal cortex (OFC) in methadone users compared with both heroin users and controls concomitant with the greatest overall tendency to 'play risky'. Heroin users showed significant under-activation in this area compared with the other two groups whilst exhibiting the greatest overall tendency to 'play safe'. Correlational analysis revealed that abnormal task-related activation of the left OFC was associated with the dose of methadone in methadone users and with the duration of intravenous heroin use in heroin users. 'Playing safe' following a loss of points was also negatively correlated with the activation of pregenual anterior cingulate and insula cortex in controls, but not in opiate users.

CONCLUSION

Our findings suggest that the interplay between processes involved in integrating penalty information for the purpose of response selection may be altered in opiate users. This change was reflected differentially in task-related pattern of OFC activation depending on the opiate used.

Phenomenologies of the akratic self: masculinity, regrets, and HIV among men on methadone

This study explores the motivational bargaining processes that constitute an "act" of heterosexual HIV risk-taking by focusing on the narrative viewpoint of two men in methadone maintenance treatment programs in the Harlem section of New York City. These men reported sexual episodes with complex motivational "event grammars" that were analyzed using qualitative methods. Building on the concept of akrasia (failure to convert intentions into action), I argue that HIV risky heterosex results from temporal displacements of instrumental rationality by two other equally relevant orientations of sexual action, namely, affectual and normative. I conclude that sexual risk occurs in the context of emotions and normative presentations of the masculine self. Consequently, a man's risk of loosing footing or consistent face vis-à-vis his female sex partner, and not the risks of HIV, becomes a priority of the sexual interaction. Sexuality is at its core social and, hence, subject to more powerful forces than personal safety or behaviorist reward.

A social network profile and HIV risk among men on methadone: do social networks matter?

The paper describes structural and HIV-related network characteristics and examines associations between these various social network domains and HIV risk behaviors among a sample of 356 men randomly selected from a methadone maintenance treatment program (MMTP) in New York City. Multiple logistic regression analyses suggest that (1) a higher level of perceived sexual risk among network members, referred to as "alters" in this study, was associated with an increased likelihood of the participant engaging in sexual risk behaviors; (2) participants who indicated that they exchanged encouragement with a higher number of network alters about using condoms were less likely to report engaging in unprotected sex; and (3) participants who indicated that they talked about HIV risks with a higher number of network alters were less likely to engage in unprotected sex in the past 6 months. Collectively, these findings support the notion that networks may influence the adoption of risk reduction strategies in this population. Implications of the findings for HIV prevention network interventions for men in MMTPs are discussed.

Does naltrexone treatment lead to depression? Findings from a randomized controlled trial in subjects with opioid dependence

OBJECTIVE

Dysphoria and depression have been cited as side effects of the opioid antagonist naltrexone. We aimed to assess whether depressive symptoms are a clinically relevant side effect in a population receiving naltrexone as a treatment for opioid dependence.

METHODS

We carried out a randomized controlled, open-label trial comparing rapid opiate detoxification under anesthesia and naltrexone treatment with continued methadone maintenance at the Alcohol and Drug Service, Royal Brisbane and Women's Hospital, Brisbane, Australia. The study subjects were patients stabilized on methadone maintenance treatment for heroin dependence who wished to transfer to naltrexone treatment. The Beck Depression Inventory, State-Trait Anxiety Inventory and Opiate Treatment Index subscales for heroin use and social functioning were used at baseline and follow-up assessments at 1, 2, 3 and 6 months.

RESULTS

Forty-two participants were allocated to receive naltrexone treatment, whereas 38 continued methadone maintenance as the control condition. Participants who received naltrexone did not exhibit worsening of depressive symptoms. In participants attending all follow-up assessments, there was a trend for those receiving naltrexone to exhibit an improvement in depression over time compared with the control group. Participants who were adherent to naltrexone treatment exhibited fewer depressive symptoms than those who were nonadherent.

CONCLUSIONS

These results suggest that depression need not be considered a common adverse effect of naltrexone treatment or a treatment contraindication and that engaging with or adhering to naltrexone treatment may be associated with fewer depressive symptoms.

Punishment induces risky decision-making in methadone-maintained opiate users but not in heroin users or healthy volunteers

Reinforcing properties of psychoactive substances are considered to be critically involved in the development and maintenance of substance dependence. While accumulating evidence suggests that the sensitivity to reinforcement values may generally be altered in chronic substance users, relatively little is known about the influence reinforcing feedback exerts on ongoing decision-making in these individuals. Decision-making was investigated using the Cambridge Risk Task, in which there is a conflict between an unlikely large reward option and a likely small reward option. Responses on a given trial were analyzed with respect to the outcome on the previous trial, providing a measure of the impact of prior feedback in modulating behavior. Five different groups were compared: (i) chronic amphetamine users, (ii) chronic opiate users in methadone maintenance treatment (MMT), (iii) chronic users of illicit heroin, (iv) ex-drug users who had been long-term amphetamine / opiate users but were abstinent from all drugs of abuse for at least 1 year and (v) matched controls without a history of illicit substance use. Contrary to our predictions, choice preference was modified in response to feedback only in opiate users enrolled in MMT. Following a loss, the MMT opiate group chose the likely small reward option significantly less frequently than controls and heroin users. Our results suggest that different opiates are associated with distinctive behavioral responses to feedback. These findings are discussed with respect to the different mechanisms of action of heroin and methadone. Neuropsychopharmacology (2005) 30, 2115-2124. doi:10.1038/sj.npp.1300812; published online 6 July 2005.

Respiratory symptom relief related to reduction in cigarette use

INTRODUCTION

Many smokers reduce their cigarette consumption during failed attempts to quit. We report the impact of changes in consumption on smoking-related respiratory symptom severity (SRRSS).

METHODS

Between February 2002 and May 2004 we recruited 383 smokers from 5 methadone maintenance programs for a randomized trial of nicotine replacement plus behavioral treatment versus nicotine replacement alone for smoking cessation. Cigarette use in the 28 days prior to the interview, and severity of SRRSS using a 7-item respiratory index, were assessed at baseline and at 3-month follow-up.

OUTCOME

Baseline minus 3-month assessment difference in SRRSS score.

RESULTS

Follow-up of 319 participants (83.3%), mean age 40.4 years, 51.4% male, who smoked 26.4 cigarettes per day, demonstrated a mean reduction of 16.7 cigarettes per day. A reduction in cigarette use was positively and significantly (b=0.29, t=5.16, P<.001) associated with a reduction in smoking-related symptom severity after adjusting for age, gender, race, years of regular smoking, baseline nicotine dependence, and history of treatment for asthma or emphysema. A 1 standard deviation reduction in average daily smoking (about 14.1 cigarettes) was associated with a 0.28 standard deviation decrease in smoking-related symptom severity.

CONCLUSION

Reduction in symptom severity increases as absolute reduction in daily smoking increases. This is the first study to demonstrate an association between subjective short-term health changes and reduction in smoking.

Attitudes and practices regarding the use of methadone in US state and federal prisons

In the United States, vigorous enforcement of drug laws and stricter sentencing guidelines over the past 20 years have contributed to an expanded incarcerated population with a high rate of drug use. One in five state prisoners reports a history of injection drug use, and many are opiate dependent. For over 35 years, methadone maintenance therapy has been an effective treatment for opiate dependence; however, its use among opiate-dependent inmates in the United States is limited. In June 2003, we conducted a survey of the medical directors of all 50 US states and the federal prison system to describe their attitudes and practices regarding methadone. Of the 40 respondents, having jurisdiction over 88% (n =1,266,759) of US prisoners, 48% use methadone, predominately for pregnant inmates or for short-term detoxification. Only 8% of respondents refer opiate-dependent inmates to methadone programs upon release. The results highlight the need to destigmatize the use of methadone in the incarcerated setting, expand access to methadone during incarceration, and to improve linkage to methadone treatment for opiate-dependent offenders who return to the community.

Personality measures in former heroin users receiving methadone or in protracted abstinence from opiates

OBJECTIVE

Methadone Maintenance Therapy (MMT) and detoxification to abstinence are among the most common treatment options for opiate-dependent patients. This paper compares personality traits in detoxified former heroin users and those on MMT in order to assess their relevance to treatment selection.

METHOD

Twenty-six formerly heroin-dependent subjects receiving MMT (MM), 33 formerly heroin-dependent subjects withdrawn from MMT (MW), and 43 healthy controls were compared on the Millon Clinical Multiaxial Inventory-II (MCMI-II) and the Temperament and Character Inventory (TCI).

RESULTS

On the TCI, MM patients had higher novelty seeking and lower self-directedness scores than controls. Both MM and MW subjects scored higher than controls on multiple MCMI-II scales. MW but not MM subjects scored higher than controls on two Cluster A Scales and the delusional disorder scale.

CONCLUSION

Schizophrenia-spectrum pathology in former opiate users may be greater than previously recognized and could potentially be relevant to treatment selection.

The prescribing of methadone and other opioids to addicts: national survey of GPs in England and Wales

BACKGROUND

GPs occupy a pivotal position in relation to providing services to opiate misusers in the UK, and this is now cited to support initiatives in other countries.

AIMS

To investigate GP involvement in the management of opiate misusers; and to examine the nature of this prescribing of methadone and other opioids.

DESIGN

GP data collected via self-completion postal questionnaire from a 10% random sample of the 30 000 GPs across England and Wales. Patient prescription data obtained on opiate misusers treated during the preceding 4 weeks.

SETTING

Primary healthcare practice in England and Wales in mid-2001.

METHOD

A questionnaire was mailed to a random 10% sample of GPs stratified by number of partners in the practice, with three follow-up mailshots. Data on drugs prescribed by these practitioners were also studied, including drug prescribed, form, dose and dispensing arrangements.

RESULTS

The response rate was 66%. Opiate misusers had been seen by 51% of GPs in the preceding 4 weeks (mean of 4.1 such patients), of whom 50% had prescribed opiate-substitution drugs. This provided a study sample of 1482 opiate misusers to whom GPs were prescribing methadone (86.7%), dihydrocodeine (8.5%) or buprenorphine (4.4%). Of 1292 methadone prescriptions, mean daily dose was 36.9 mg - 47.9% being for 30 mg or less. Daily interval dispensing was stipulated by 44.6%, while 42.9% permitted weekly take-away supply.

CONCLUSIONS

In 2001 nearly three times as many GPs were seeing opiate misusers than was the case in 1985. Half were prescribing substitute-opiate drugs such as methadone (to an estimated 30 000 patients). However, there are grounds for concern about the quality of this prescribing. Most doses were too low to constitute optimal methadone maintenance; widespread disregard of the availability of supervised or interval dispensing increases the risks of diversion to the blackmarket and deaths from methadone overdose. Increased quantity of care has been achieved. Increased quality is now required.

An implementation evaluation

BACKGROUND

Methadone is effective treatment for opioid addiction, but regulations restrict its use. Methadone medical maintenance treats stabilized methadone patients in a medical setting, but only experimental programs have been studied.

OBJECTIVE

To evaluate the implementation of the first methadone medical maintenance program established outside a research setting.

DESIGN

One-year program evaluation.

SETTING

A public hospital and a community opioid treatment program.

PARTICIPANTS

Methadone patients with >1 year of clinical stability. Eleven generalist physicians and 4 hospital pharmacists.

INTERVENTIONS

Regulatory exemptions were requested. Physicians and pharmacists were trained. Patients were transferred to the medical setting and permitted 1-month supplies of methadone.

MEASUREMENTS

Patient eligibility and willingness to enroll, treatment retention, urine toxicology results, change in addiction severity and functional status, medical services provided, patient and physician satisfaction, and physician attitudes toward methadone maintenance.

RESULTS

Regulatory exemptions were obtained after a 14-month process, and the program was cited in federal policy as acceptable for widespread implementation. Forty-nine of 684 patients (7.2%) met stability criteria, and 30 enrolled. Twenty-eight were retained for 1 year, and 2 transferred to other programs. Two patients had opioid-positive urine tests and were managed in the medical setting. Previously unmet medical needs were addressed, and the Addiction Severity Index (ASI) medical composite score improved over time (P=.02). Patient and physician satisfaction were high, and physician attitudes toward methadone maintenance treatment became more positive (P=.007).

CONCLUSIONS

Methadone medical maintenance is complex to arrange but feasible outside a research setting, and can result in good clinical outcomes.

The effectiveness of community maintenance with methadone or buprenorphine for treating opiate dependence

BACKGROUND

Opiate dependence is a major health and social issue in many countries. A mainstay of therapy has been methadone maintenance treatment, but other treatments, particularly buprenorphine, are increasingly being considered.

AIM

To conduct a systematic review to synthesise and critically appraise the evidence on the effectiveness of community maintenance programmes with methadone or buprenorphine in treating opiate dependence.

METHOD

A systematic review of databases, journals and the grey literature was carried out from 1990-2002. Inclusion criteria were: community-based, randomised controlled trials of methadone and/or buprenorphine for opiate dependence involving subjects who were aged 18 years old or over.

RESULTS

Trials were set in a range of countries, employed a variety of comparators, and suffered from a number of biases. The evidence indicated that higher doses of methadone and buprenorphine are associated with better treatment outcomes. Low-dose methadone (20 mg per day) is less effective than buprenorphine (2-8 mg per day). Higher doses of methadone (>50-65 mg per day) are slightly more effective than buprenorphine (2-8 mg per day). There was some evidence that primary care could be an effective setting to provide this treatment, but such evidence was sparse.

CONCLUSION

The literature supports the effectiveness of substitute prescribing with methadone or buprenorphine in treating opiate dependence. Evidence is also emerging that the provision of methadone or buprenorphine by primary care physicians is feasible and may be effective.

Drug misuse: a review of treatments

Treating drug users is something that every health professional should be able to do, whether providing brief interventions or harm minimisation advice or providing an assessment and directing the user for further care. Unfortunately, despite a growing problem, few health professionals outside specialist addiction services have the skills, experience and knowledge to provide patients with effective pharmacological interventions. Many of the pharmacological treatment options, such as methadone maintenance, have had extensive research and have been shown to be effective in a number of outcome areas. Newer treatments, such as buprenorphine- and naltrexone-assisted detoxification have a growing research base. This article provides a brief overview of treatments options and the impact of drug use on social and medical care services.

Buprenorphine and methadone in the treatment of opioid dependence: methods and design of the COBRA study

Buprenorphine and methadone are the two established substitution drugs licensed in many countries for the treatment of opioid dependence. Little is known, however, about how these two drugs are applied and how they work in clinical practice. In this paper we present the aims, methods, design and sampling issues of a collaborative multi-stage epidemiological study (COBRA) to address these issues. Based on a nationally representative sample of substitution physicians, the study is designed as an observational, naturalistic study, consisting of three major parts. The first part was a national survey of substitution doctors (prestudy, n = 379 doctors). The second part was a cross-sectional study (n = 223 doctors), which consisted of a target-week assessment of 2,694 consecutive patients to determine (a) the severity and problem profiles and treatment targets; (b) the choice and dosage scheme of the substitution drug; (c) past and current interventions, including treatment of comorbid hepatitis C; and (d) cross-sectional differences between the two drugs with regard to comorbidity, clinical course, acceptance/compliance and social integration. The third part consists of a prospective-longitudinal cohort study of 48 methadone-treated and 48 buprenorphine-treated patients. The cohort is followed up over a period of 12 months to investigate whether course and outcome of the patients differ by type or treatment received in terms of clinical, psychosocial, pharmaco-economic and other related measures. The response rate among substitution doctors was 57.1%; that among eligible patients was 71.7%. Comparisons with the federal registers reveal that the final samples of doctors and patients may be considered nationally representative with regard to regional distribution, training, type of setting as well as the frequency of patients treated with buprenorphine or methadone. The COBRA study provides a unique comprehensive database, informing about the natural allocation and intervention processes in routine care and about the course and outcome of patients treated with buprenorphine or methadone.

Jail management of arrestees/inmates enrolled in community methadone maintenance programs

Anecdotal evidence suggests that many jails fail to adequately detoxify arrestees/inmates who are enrolled in methadone programs, but there are few empirical data. The objective of this study was to assess how jails manage arrestees/inmates enrolled in methadone programs. A national survey of 500 jails in the United States was conducted. Surveys were mailed to the 200 largest jails in the country in addition to a random sample of 300 of the remaining jails (10% sample). Jails were specifically asked about management of opiate dependency among arrestees/inmates enrolled in methadone programs. Weighted logistic regression analyses were conducted to assess predictors of continuing methadone during incarceration and use of recommended detoxification protocols. Among the 245 (49%) jails that responded, only 1 in 4 (27%) reported they contacted the methadone programs regarding dose, and only 1 in 8 (12%) continued methadone during the incarceration. Very few (2%) jails used methadone or other opiates for detoxification. Most used clonidine. However, half (48%) of jails failed to use clonidine, methadone, or other opiates to detoxify inmates from methadone. Weighted logistic regression models showed that moderately large jails and those located in the South and Midwest were significantly more likely to continue methadone. Very large jails, those with an estimated prevalence of opiate dependence of 6%-10% among arrestees/inmates, and those located in the Northeast were significantly more likely to use recommended detoxification protocols. Very few jails provided continuous treatment to arrested persons on methadone, and half failed to detoxify arrestees/inmates using recommended protocols. These practices jeopardize the health and well-being of persons enrolled in methadone programs and underscore the need for uniform national policies within jails.

Bioavailabilities of rectal and oral methadone in healthy subjects

AIMS

Rectal administration of methadone may be an alternative to intravenous and oral dosing in cancer pain, but the bioavailability of the rectal route is not known. The aim of this study was to compare the absolute rectal bioavailability of methadone with its oral bioavailability in healthy humans.

METHODS

Seven healthy subjects (six males, one female, aged 20-39 years) received 10 mg d(5)-methadone-HCl rectally (5 ml in 20% glycofurol) together with either d(0)-methadone intravenously (5 mg) or orally (10 mg) on two separate occasions. Blood samples for the LC-MS analyses of methadone and it's metabolite EDDP were drawn for up to 96 h. Noninvasive infrared pupillometry was performed at the same time as blood sampling.

RESULTS

The mean absolute rectal bioavailability of methadone was 0.76 (0.7, 0.81), compared to 0.86 (0.75, 0.97) for oral administration (mean (95% CI)). Rectal absorption of methadone was more rapid than after oral dosing with Tmax values of 1.4 (0.9, 1.8) vs. 2.8 (1.6, 4.0) h. The extent of formation of the metabolite EDDP did not differ between routes of administration. Single doses of methadone had a duration of action of at least 10 h and were well tolerated.

CONCLUSIONS

Rectal administration of methadone results in rapid absorption, a high bioavailability and long duration of action. No evidence of presystemic elimination was seen. Rectal methadone has characteristics that make it a potential alternative to intravenous and oral administration, particularly in cancer pain and palliative care.

The effect of quinidine, used as a probe for the involvement of P-glycoprotein, on the intestinal absorption and pharmacodynamics of methadone

AIMS

There is considerable unexplained interindividual variability in the methadone dose-effect relationship. The efflux pump P-glycoprotein (P-gp) regulates brain access and intestinal absorption of many drugs. Evidence suggests that methadone is a P-gp substrate in vitro, and P-gp affects methadone analgesia in animals. However the role of P-gp in human methadone disposition and pharmacodynamics is unknown. This investigation tested the hypothesis that the intestinal absorption and pharmacodynamics of oral and intravenous methadone are greater after inhibition of intestinal and brain P-gp, using the P-gp inhibitor quinidine as an in vivo probe.

METHODS

Two randomized, double-blind, placebo-controlled, balanced crossover studies were conducted in healthy subjects. Pupil diameters and/or plasma concentrations of methadone and the primary metabolite EDDP were measured after 10 mg intravenous or oral methadone HCl, dosed 1 h after oral quinidine (600 mg) or placebo.

RESULTS

Quinidine did not alter the effects of intravenous methadone. Miosis t(max) (0.3 +/- 0.3 vs 0.3 +/- 0.2 h (-0.17, 0.22)), peak (5.3 +/- 0.8 vs 5.1 +/- 1.0 mm (0.39, 0.84)) and AUC vs time (25.0 +/- 5.7 vs 26.8 +/- 7.1 mm h (-6.1, 2.5)) were unchanged (placebo vs quinidine (95% confidence interval on the difference)). Quinidine increased (P < 0.05) plasma methadone concentrations during the absorptive phase, decreased t(max) (2.4 +/- 0.7 vs 1.6 +/- 0.9 h (0.33, 1.2)), and increased peak miosis (3.2 +/- 1.5 vs 4.3 +/- 1.6 mm (-1.96, -0.19)) after oral methadone. The C(max) (55.6 +/- 10.3 vs 59.4 +/- 14.1 ng ml(-1) (-8.5, 0.65)) and AUC of methadone (298 +/- 46 vs 316 +/- 74 ng ml(-1) h (-54, 18)) were unchanged, as were the EDDP : methadone AUC ratios. Quinidine had no effect on the rate constant for transfer of methadone between plasma and effect compartment (k(e0)) (2.6 +/- 2.6 vs 2.5 +/- 1.4 h(-1) (-3.5, 4.2)).

CONCLUSIONS

Quinidine increased the plasma concentrations of oral methadone in the absorptive phase and the miosis caused by methadone, suggesting that intestinal P-gp affects oral methadone absorption and hence its clinical effects. Quinidine had no effect on methadone pharmacodynamics after intravenous administration, suggesting that if quinidine is an effective inhibitor of brain P-gp, then P-gp does not appear to be a determinant of the access of methadone to the brain.

Accessibility of addiction treatment: results from a national survey of outpatient substance abuse treatment organizations

OBJECTIVES

This study examined organization-level characteristics associated with the accessibility of outpatient addiction treatment.

METHODS

Program directors and clinical supervisors from a nationally representative panel of outpatient substance abuse treatment units in the United States were surveyed in 1990, 1995, and 2000. Accessibility was measured from clinical supervisors' reports of whether the treatment organization provided "treatment on demand" (an average wait time of 48 hours or less for treatment entry), and of whether the program turned away any patients.

RESULTS

In multivariable logistic models, provision of "treatment on demand" increased two-fold from 1990 to 2000 (OR, 1.95; 95 percent CI, 1.5 to 2.6), while reports of turning patients away decreased nonsignificantly. Private for-profit units were twice as likely to provide "treatment on demand" (OR, 2.2; 95 percent CI, 1.3 to 3.6), but seven times more likely to turn patients away (OR, 7.4; 95 percent CI, 3.2 to 17.5) than public programs. Conversely, units that served more indigent populations were less likely to provide "treatment on demand" or to turn patients away. Methadone maintenance programs were also less likely to offer "treatment on demand" (OR, .65; 95 percent CI, .42 to .99), but more likely to turn patients away (OR, 2.4; 95 percent CI, 1.4 to 4.3).

CONCLUSIONS

Although the provision of timely addiction treatment appears to have increased throughout the 1990s, accessibility problems persist in programs that care for indigent patients and in methadone maintenance programs.

Screening for sexually transmitted infections in substance abuse treatment programs

OBJECTIVES

We evaluated the prevalence of the sexually transmitted infections (STIs) chlamydia and gonorrhea in clients at a methadone maintenance program and a residential detoxification program.

METHODS

We collected urine specimens for chlamydia and gonorrhea ligase chain reaction testing and assessed sexual, substance abuse and STI histories.

RESULTS

Of 700 subject assessments, 490 occurred among detoxification clients and 210 in methadone maintenance. Chlamydia trachomatis was detected in 5/700 (0.9, 95% CI=0.1-1.8%) and Neisseria gonorrhoeae in none. All chlamydia infected subjects were recruited from the detoxification program. Subjects reported high risk sexual behavior: 17% reported commercial sex exchange, and 22% reported inconsistent condom use with multiple sexual partners during the prior 2 months.

CONCLUSION

Based on prevalence in Boston, MA, universal screening for STI in substance abuse treatments programs is not warranted. However, routine screening for younger substance abusers and in communities with high prevalence should be considered.

Opioids - Effects on Human Performance and Behavior

The purpose of the monograph is to provide readers with a summary of the literature relating selected opioids to performance issues, specifically driving. This monograph provides a summary of information to aid expert witnesses in preparing for court testimony. Information for codeine, hydrocodone, hydromorphone, methadone, morphine, and oxycodone is provided. In addition to a review of performance studies, a summary of acute and chronic pharmacology, pharmacokinetics, and metabolism is included. Opioids appear to impair psychomotor functioning likely to be important to the performance of complex, divided attention tasks such as driving. This impairment is notably more prevalent in individuals with no history of opioid use; individuals with long-term opioid use do not demonstrate as extensive of an impairment. Other factors such as personality, environment, and pain control also sharply modulate opioid impairment.

Beliefs about methadone in an inner-city methadone clinic

Despite being considered both the most effective treatment for heroin addiction and an essential tool in the prevention of human immunodeficiency virus (HIV), methadone maintenance (MM) is often held in low esteem by heroin addicts-even those in MM treatment. This survey examined current beliefs and attitudes about MM of patients at an inner-city clinic, and the personal experience and attitudes of these patients with this treatment. Consenting patients in a methadone clinic serving a poor population with high rates of human immunodeficiency virus infection were queried about their attitudes toward and beliefs about methadone using a 16-item questionnaire. Over 2 days, 315 questionnaires were completed (acceptance rate 40%), totaling 32% of the 1,000 clinic patients. Nearly 80% believed that methadone had a positive effect on his or her life, but 80% were certain or unsure as to whether methadone is bad for one's health, and a similar percentage (80%) believed that discontinuing methadone was an important goal. Patients continue to have strongly negative attitudes toward and beliefs about methadone despite their acknowledgement that methadone has been very positive for them as individuals. As a result, many patients leave MM treatment prematurely, and there are usually unfilled slots in MM programs in New York City, even while continued need exists (e.g., less than 25% of the heroin addicts in the city are in treatment). The restrictive nature of many MM programs may account for these attitudes and beliefs.

Olanzapine-induced hyperventilation: case report

Although olanzapine therapy has been associated with fewer extrapyramidal side effects than the traditional antipsychotic medications, reported side effects include dystonia, tardive dyskinesia, hypotension, diabetes mellitus, seizures and neuroleptic malignant syndrome. There are no previous published reports of hyperventilation associated with olanzapine therapy, but we present the case of a male patient who developed dyspnea and hyperventilation while taking olanzapine.

Policy progress for physician treatment of opiate addiction

Medical treatment of heroin addiction with methadone and other pharmacotherapies has important benefits for individuals and society. However, regulatory policies have separated this treatment from the medical care system, limiting access to care and contributing to the social stigma of even effective addiction pharmacotherapy. Increasing problems caused by heroin addiction have added urgency to the search for policies and programs that improve the access to and quality of opiate addiction treatment. Recent initiatives aiming to reintegrate methadone maintenance and other addiction pharmacotherapies into medical practice may promote both expanded treatment capacity and increased physician expertise in addiction medicine. These initiatives include changes in federal oversight of the opiate addiction treatment system, the approval of physician office-based methadone maintenance programs for stabilized patients, and federal legislation that could enable physicians to treat opiate addiction with new medications in regular medical practice.

Policy progress for physician treatment of opiate addiction

Medical treatment of heroin addiction with methadone and other pharmacotherapies has important benefits for individuals and society. However, regulatory policies have separated this treatment from the medical care system, limiting access to care and contributing to the social stigma of even effective addiction pharmacotherapy. Increasing problems caused by heroin addiction have added urgency to the search for policies and programs that improve the access to and quality of opiate addiction treatment. Recent initiatives aiming to reintegrate methadone maintenance and other addiction pharmacotherapies into medical practice may promote both expanded treatment capacity and increased physician expertise in addiction medicine. These initiatives include changes in federal oversight of the opiate addiction treatment system, the approval of physician office-based methadone maintenance programs for stabilized patients, and federal legislation that could enable physicians to treat opiate addiction with new medications in regular medical practice.

Distribution of R- and S-methadone into human milk during multiple, medium to high oral dosing

AIMS

To measure the interdose milk to plasma ratio (M/P) of R- and S-methadone during multiple dosing in lactating mothers taking medium to high doses of methadone (> 40 mg daily), and to assess likely infant exposure.

METHODS

Eight mother/child pairs were studied, initially during their postpartum hospital stay (immature milk), and where possible again after 15 days (mature milk). The women were on a methadone maintenance programme with daily doses of >or=40 mg day-1. Venous blood was collected at 0, 1, 2, 4, 6, 8, 12, and 24 h and milk was collected from both breasts at 0-4, 4-8, 8-12, 12-16, 16-20, and 20-24 h after dose. R- and S-methadone were quantified by h.p.l.c. The areas under the plasma and milk concentration-time curves (AUC) were estimated and M/P(AUC) was calculated. The relative infant dose of both enantiomers was estimated as the product of drug concentration in milk and an average daily milk intake of 0.15 l kg(-1).

RESULTS

For immature milk (n = 8) the M/P(AUC) for R-methadone was 0.68 (95% CI 0.48, 0.89) and for S-methadone 0.38 (0.26, 0.50). For mature milk (n = 2) the M/P(AUCs) for R-methadone were 0.39 and 0.54 and for S-methadone 0.24 and 0.30, respectively. The estimated doses of R- and S-methadone that would be received by the infant via immature milk were 3.5% (2.05, 5.03%) and 2.1% (1.3, 2.8%), respectively, of the maternal dose (assuming 50% of each enantiomer in the dose). The relative infant dose for R- plus S-methadone together was 2.8% (1.7, 3.9%).

CONCLUSIONS

Breastfeeding during medium to high dose methadone appears to be 'safe' according to conventional criteria because the dosage is < 10%. However because the absolute dose received by the infant is dependent on the maternal dose rate, the risk-benefit ratio should be considered for each individual case. The doses of methadone received via milk are unlikely to be sufficient to prevent the neonatal abstinence syndrome.

A single dose of methadone inhibits cytochrome P-4503A activity in healthy volunteers as assessed by the urinary cortisol ratio

AIMS

To examine the effect of a single oral dose of methadone on cytochrome P450 (CYP) 3A activity using the urinary 6beta-hydroxycortisol to cortisol ratio (UCR) as a marker of CYP3A activity.

METHODS

A single oral dose (0.2 mg kg-1) of rac-methadone was administered to eight healthy female volunteers. Frequent blood samples and all urine over seven time periods was collected for 96 h following dosing. The UCR and the concentration of the major CYP3A metabolite of methadone, EDDP, were measured in urine. Methadone enantiomer concentrations were determined in plasma and urine. All quantifications were performed by validated high performance liquid chromatography assays.

RESULTS

In all volunteers a significant decline of the UCR from immediately predose values was observed at the 4-8 and 8-12 h collection periods (P < 0.05, 95% CI for the differences: 0.4,16 and 0.6,16, respectively) with a return to immediately predose values after 2-3 days, suggesting methadone was an inhibitor of CYP3A. The UCR was found to be significantly correlated with the amount of EDDP excreted in the urine and with the area under the plasma concentration vs time profile for total (R + S) methadone, supporting in vitro data that CYP3A is primarily responsible for EDDP formation and has a significant influence on methadone disposition.

CONCLUSIONS

Methadone appears to be a CYP3A inhibitor in vivo following a single oral dose and measurements of the urinary cortisol ratio appear to be a useful index to follow this inhibition.

The pharmacokinetics of methadone in HIV-positive patients receiving the non-nucleoside reverse transcriptase inhibitor efavirenz

AIMS

Methadone is predominantly metabolized by cytochrome P450 3A4 and the non nucleoside reverse transcriptase inhibitor (NNRTI) efavirenz is a recognized inducer of this enzyme. We evaluated the pharmacokinetics of methadone in the presence and absence of efavirenz when administered to HIV infected patients with a history of injection drug use (IDU).

METHODS

Eleven patients on stable methadone maintenance therapy, due to commence antiretroviral therapy (ART), participated in this study. Steady state methadone kinetic profiles were obtained on two occasions 0, 1, 2, 3, 4, 5, 6, 7, 8 and 24 h post dosing. Following centrifugation, separated plasma was heated at 58 degrees C for 30 min to inactivate HIV and stored at -80 degrees C until methadone analysis by high performance liquid chromatography.

RESULTS

When combined with efavirenz there was a marked decrease in the maximum plasma concentration (Cmax) of methadone from 689 (range 212-1568) to 358 (range 205-706) ng ml(-1), P = 0.007 : 95% confidence interval (CI) 112-549. The mean area under the methadone concentration curve 0-24 h (AUC(0,24 h)) was also significantly reduced from 12341 (range 3682-34147) to 5309 (range 2430-10349) ng ml(-1) h in the presence of efavirenz, P = 0.012 : 95% CI 1921-12143. Nine patients described symptoms of methadone withdrawal and received a dose increase. Although methadone AUC(0,24 h) was reduced by over 50% following efavirenz the mean increase in methadone dose required was 22% (range 15-30 mg).

CONCLUSION

The inclusion of the NNRTI efavirenz in once daily ART for HIV patients with a history of IDU receiving methadone maintenance results in a significant reduction in methadone plasma concentrations mediated by enzyme induction. It is important to distinguish efavirenz neurological effects which were observed between days 1-5 of therapy from symptoms of methadone withdrawal which occurred from day 8 onwards. The dose of methadone was adjusted by increments of 10 mg to counteract the efavirenz inducing effect.

Steady-state pharmacokinetics of (R)- and (S)-methadone in methadone maintenance patients

AIMS

To investigate the steady-state pharmacokinetics of (R)- and (S)-methadone in a methadone maintenance population.

METHODS

Eighteen patients recruited from a public methadone maintenance program underwent an interdosing interval pharmacokinetic study. Plasma and urine samples were collected and analysed for methadone and its major metabolite (EDDP) using stereoselective h.p.l.c. Methadone plasma protein binding was examined using ultrafiltration, and plasma alpha1-acid glycoprotein concentrations were quantified by radial immunoassay.

RESULTS

(R)-methadone had a significantly (P < 0.05) greater unbound fraction (mean 173%) and total renal clearance (182%) compared with (S)-methadone, while maximum measured plasma concentrations (83%) and apparent partial clearance of methadone to EDDP (76%) were significantly (P < 0.001) lower. When protein binding was considered (R)-methadone plasma clearance of the unbound fraction (59%) and apparent partial intrinsic clearance to EDDP (44%) were significantly (P < 0.01) lower than for (S)-methadone, while AUCtau_¿u¿ss (167%) was significantly (P < 0. 001) greater. There were no significant (P > 0.2) differences between the methadone enantiomers for AUCtauss, steady-state plasma clearance, trough plasma concentrations and unbound renal clearance. Patients excreted significantly (P < 0.0001) more (R)-methadone and (S)-EDDP than the corresponding enantiomers. Considerable interindividual variability was observed for the pharmacokinetic parameters, with coefficients of variation of up to 70%.

CONCLUSIONS

Steady-state pharmacokinetics of unbound methadone are stereoselective, and there is large interindividual variability consistent with CYP3A4 mediated metabolism to the major metabolite EDDP; the variability did not obscure a significant dose-plasma concentration relationship. Stereoselective differences in the pharmacokinetics of methadone may have important implications for pharmacokinetic-pharmacodynamic modelling but is unlikely to be important for therapeutic drug monitoring of methadone, in the setting of opioid dependence.

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.

Methadone distribution and excretion into breast milk of clients in a methadone maintenance programme

AIMS

Methadone is widely used in maintenance programs for opioid-dependent subjects. The aims of the study were to quantify the distribution and excretion of methadone in human milk during the early postnatal period and to investigate exposure of breast fed infants to the drug.

METHODS

Blood and milk samples were obtained from 12 breast feeding women who were taking methadone in daily doses ranging from 20-80 mg (0.3-1.14 mg kg-1). Blood was also obtained from eight of their infants. Methadone concentration in these samples was quantified by h.p.l.c. The infants were observed for withdrawal symptoms.

RESULTS

The mean (95% CI) milk/plasma ratio was 0.44 (0.24-0.64). Exposure of the infants, calculated assuming an average milk intake of 0.15 l kg-1 day-1 and a bioavailability of 100% was 17.4 (10.8-24) microg kg-1 day-1. The mean infant dose expressed as a percentage of the maternal dose was 2.79 (2.07-3.51)%. Methadone concentrations in seven infants were below the limit of detection for the h.p.l.c. assay procedure, while one infant had a plasma methadone concentration of 6.5 microg l-1. Infant exposure to methadone via human milk was insufficient to prevent the development of a neonatal abstinence syndrome which was seen in seven (64%) infants. No adverse effects attributable to methadone in milk were seen.

CONCLUSIONS

We conclude that exposure of breast fed infants to methadone taken by their mothers is minimal and that women in methadone maintenance programs should not be discouraged from breast feeding because of this exposure.

The pharmacokinetics of methadone in healthy subjects and opiate users

AIMS

There is some evidence that monitoring methadone plasma concentration may be of benefit in dosage adjustment during methadone maintenance therapy for heroin (opiate) dependence. However, the kinetics of oral methadone are incompletely characterized. We attempted to describe the latter using a population approach combining intensive 57 h sampling data from healthy subjects with less intensive sparse 24 h data from opiate users.

METHODS

Single oral doses of rac-methadone were given to 13 drug-naive healthy subjects (7 men and 6 women) and 17 opiate users beginning methadone maintenance therapy (13 men and 4 women). Plasma methadone concentrations were measured by h.p.l.c. Kinetic analysis was performed using the P-Pharm software.

RESULTS

Comparison of kinetic models incorporating mono- or biexponential disposition functions indicated that the latter best represented the data. The improvement was statistically significant for the data from healthy subjects whether the full 57 h or truncated 24 h profiles were used (P<0.031 and P<0.024, respectively), while it was of borderline significance for the more variable data from opiate users (P=0.057) or for pooled (healthy subjects and opiate users) data (P=0.066). The population mean oral clearance of methadone was 6.9+/-1.5 s.d. l h(-1) (5.3+/-1.2 s.d. l h(-1) using 0-24 h data) in the healthy subjects. The results of separate analyses of the data from opiate users and healthy subjects were in contrast with those obtained from pooled data analysis. The former indicated a significantly lower clearance for opiate users (3.2+/-0.3 s.d. l h(-1), P<0.001); 95% CI for the difference = -3 to -6 l h(-1) and no difference in the population mean values of V/F (212+/-27 s.d. l and 239+/-121 s.d. l, P=0.15), while according to the latter analysis addiction was a covariate for V/F but not for oral clearance. A slower absorption of methadone in opiate users was indicated from the analysis of both pooled and separate data. The median elimination half-life of methadone in healthy subjects was 33-46 h depending on the method used to calculate this parameter.

CONCLUSIONS

Estimates of the long terminal elimination half-life of methadone (33-46 h in healthy subjects and, possibly, longer in opiate users) indicated that accurate measurement of this parameter requires a duration of sampling longer than that used in this study. Our analysis also suggested that parameters describing plasma concentrations of methadone after a single oral dose in healthy subjects may not be used for predicting and adjusting dosage in opiate users receiving methadone maintenance therapy unless coupled with feedback concentration monitoring techniques (for example Bayesian forecasting).

Effect of acute and chronic tramadol on [3H]-5-HT uptake in rat cortical synaptosomes

1. Tramadol hydrochloride is a centrally acting opioid analgesic, the efficacy and potency of which is only five to ten times lower than that of morphine. Opioid, as well as non-opioid mechanisms, may participate in the analgesic activity of tramadol. 2. [3H]-5-hydroxytryptamine (5-HT) uptake in rat isolated cortical synaptosomes was studied in the presence of tramadol, desipramine, fluoxetine, methadone and morphine. Methadone and tramadol inhibited synaptosomal [3H]-5-HT uptake with apparent Kis of 0.27 +/- 0.04 and 0.76 +/- 0.04 microM, respectively. Morphine essentially failed to inhibit [3H]-5-HT uptake (Ki 0.50 +/- 0.30 M). 3. Methadone, morphine and tramadol were active in the hot plate test with ED50s of 3.5, 4.3 and 31 mg kg-1, respectively. At the highest tested dose (80 mg kg-1) tramadol produced only 77 +/- 5.3% of the maximal possible effect. 4. When [3H]-5-HT uptake was examined in synaptosomes prepared from rats 30 min after a single dose of morphine, methadone or tramadol, only tramadol (31 mg kg-1, s.c., equal to the ED50 in the hot plate test) and methadone (35 mg kg-1, s.c., equal to the ED90 in the hot plate test) decreased uptake. 5. Animals were chronically treated for 15 days with increasing doses of tramadol or methadone (5 to 40 mg kg-1 and 15 to 120 mg kg-1, s.c., respectively). Twenty-four hours after the last drug injection, a challenge dose of methadone (35 mg kg-1, s.c.) or tramadol (31 mg kg-1, s.c.) was administered. [3H]-5-HT uptake was not affected in synaptosomes prepared from rats chronically-treated with methadone, whereas chronic tramadol was still able to reduce this parameter by 42%. 6. Rats chronically-treated with methadone showed a significant increase in [3H]-5-HT uptake (190%) 72 h after drug withdrawal. In contrast, [3H]-5-HT uptake in rats chronically-treated with tramadol (110%) did not differ significantly from control animals. 7. These results further support the hypothesis that [3H]-5-HT uptake inhibition may contribute to the antinociceptive effects of tramadol. The lack of tolerance development of [3H]-5-HT uptake, together with the absence of behavioural alterations after chronic tramadol treatment, suggest that tramadol has an advantage over classical opioids in the treatment of pain disorders.