Drug interactions with methadone

Methadone: a review of drug-drug and pathophysiological interactions

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

Stereo-selective metabolism of methadone by human liver microsomes and cDNA-expressed cytochrome P450s: a reconciliation

In vitro metabolism of methadone was investigated in cytochrome P450 (CYP) supersomes and phenotyped human liver microsomes (HLMs) to reconcile past findings on CYP involvement in stereo-selective metabolism of methadone. Racaemic methadone was used for incubations; (R)- and (S)-methadone turnover and (R)- and (S)-EDDP formation were determined using chiral liquid chromatography-tandem mass spectrometry. CYP supersome activity for methadone use and EDDP formation ranked CYP2B6 > 3A4 > 2C19 > 2D6 > 2C18, 3A7 > 2C8, 2C9, 3A5. After abundance scaling, CYP3A4, 2B6 and 2C19 accounted for 63-74, 12-32 and 1. 4-14% of respective activity. CYP2B6, 2D6 and 2C18 demonstrated a preference for (S)-EDDP formation; CYP2C19, 3A7 and 2C8 for (R)-EDDP; 3A4 none. Correlation analysis with 15 HLMs supported the involvement of CYP2B6 and 3A. The significant correlation of S/R ratio with CYP2B6 activity confirmed its stereo-selectivity. CYP2C19 and 2D6 inhibitors and monoclonal antibody (mAb) did not inhibit EDDP formation in HLM. Chemical and mAb inhibition of CYP3A in high 3A activity HLM reduced EDDP formation by 60-85%; inhibition of CYP2B6 in 2B6 high-activity HLM reduced (S)-EDDP formation by 80% and (R)-EDDP formation by 55%. Inhibition changed methadone metabolism in a stereo-selective manner. When CYP3A was inhibited, 2B6 mediated (S)-EDDP formation predominated; S/R stereo-selectivity increased. When 2B6 was inhibited (S)-EDDP formation fell and stereo-selectivity decreased. The results confirmed the primary roles of CYPs 3A4 and 2B6 in methadone metabolism; CYP2C8 and 2C9 did not appear involved; 2C19 and 2D6 have minimal roles. CYP2B6 is the primary determinant of stereo-selective metabolism; stereo-selective inhibition might play a role in varied plasma concentrations of the two enantiomers.

Pharmacotherapy in the treatment of addiction: methadone

Methadone maintenance treatment (MMT) is the most widely available pharmacotherapy for opioid addiction and has been shown to be an effective and safe treatment over a period of 40 years. Although women comprise approximately 40% of clients currently being treated in MMT programs, comparatively little research geared specifically toward this group has been published. This article begins with an overview of neurobiological studies on opioid addiction, including a discussion of gender differences, followed by a review of the pharmacology of methadone. The authors then examine the particular needs and differences of women being treated in MMTs, including co-dependence with other substances, women's health issues, and psychosocial needs unique to this population. Research shows that women have different substance abuse treatment needs in comparison to their male counterparts. One New York City MMT program that has attempted to address these differences is highlighted.

Cancer pain and analgesia

Pain ranges in prevalence from 14-100% among cancer patients and occurs in 50-70% of those in active treatment. Cancer pain may result from direct invasion of tumor into nerves, bones, soft tissue, ligaments, and fascia, and may induce visceral pain through distension and obstruction. Cancer pain is multifaceted. Clinicians may describe cancer pain as acute, chronic, nociceptive (somatic), visceral, or neuropathic. Despite implementation of the WHO guidelines, reports of undertreatment of cancer pain persist in various clinical settings and in spite of decades of work to reduce unnecessary discomfort. Substantial obstacles to adequate pain relief with opioids include specific concerns of patients themselves, their family members, physicians, nurses, and the healthcare system. The WHO analgesic ladder serves as the mainstay of treatment for the relief of cancer pain in concert with tumoricidal, surgical, interventional, radiotherapeutic, psychological, and rehabilitative modalities. This multidimensional approach offers the greatest potential for maximizing analgesia and minimizing adverse effects. Primary therapies are directed at the source of the cancer pain and may enhance a patient's function, longevity, and comfort. Adjuvant therapies include nonopioids that confer analgesic effects in certain medical conditions but primarily treat conditions that do not involve pain. Nonopioid medications (over-the-counter agents) are useful in the management of mild to moderate pain, and their continuation through step 3 of the WHO ladder is an option after weighing a drug's risks and benefits in individual patients. Symptomatic treatment of severe cancer pain should begin with an opioid, regardless of the mechanism of the pain. They are very effective analgesics, titrate easily, and offer a favorable risk/benefit ratio. Cancer pain remains inadequately controlled despite the diagnostic and therapeutic means of ensuring that patients feel comfortable during their illness. Therefore, all practitioners need to make control of cancer pain a professional duty, even if they can only use the most basic and least expensive analgesic medications, such as morphine, codeine, and acetaminophen, to reduce human suffering.

ABCB1 (MDR1) genetic variants are associated with methadone doses required for effective treatment of heroin dependence

Methadone is a mu-opioid receptor agonist used for treating opiate dependence. The range of effective methadone doses is broad. Part of the large inter-individual variability in efficacy may be accounted for by genetic factors. Methadone is a substrate of the transporter P-glycoprotein (P-gp) 170 that is encoded by the ABCB1 (MDR1) gene. Thus, P-gp variants may play a role in methadone absorption and distribution. We assessed the association between ABCB1 polymorphisms and methadone dose requirements in 98 methadone-maintained patients. The stabilizing methadone doses were normally distributed with a mean and median dose of 160 mg/day (range 30-280 mg/day). Statistical analysis showed significant difference in genotype frequencies between the 'higher' (>150 mg/day) and 'lower' (< or =150 mg/day) methadone dose groups for single nucleotide polymorphism (SNP) 1236C>T (rs1128503) (experiment-wise P = 0.0325). Furthermore, individuals bearing the 3-locus genotype pattern TT-TT-TT (rs1045642, rs2032582 and rs1128503) have an approximately 5-fold chance of requiring the 'higher' methadone dose, while individuals heterozygous for these three SNPs have an approximately 3-fold chance of stabilizing at the 'lower' methadone dose (point-wise P-value = 0.026). These data suggest that specific ABCB1 variants may have clinical relevance by influencing the methadone dose required to prevent withdrawal symptoms and relapse in this population.

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).

Evolving perspectives on neurobiological research on the addictions: celebration of the 30th anniversary of NIDA

The roots of the Laboratory of the Biology of the Addictive Diseases are in the development of methadone maintenance for the treatment of opiate addiction. Methadone maintenance therapy continues to be one of the major effective forms of addiction pharmacotherapy and underscores the importance of biological factors in the physiology and treatment of the addictive diseases. Recent work in the Laboratory has focused on the neurobiological, neurochemical, neuroendocrine and behavioral aspects of addictive diseases (principally cocaine and the opiate addictions), using an interdisciplinary approach. The models we have focused on range from in vitro molecular biology and neuroscience, to in vivo animal models, to experiments in normal human populations and patients with specific addictive diseases, and most recently to the human molecular genetics of different addictive diseases. Two long-term corollary hypotheses have guided the Laboratory's work: (1) That the endogenous opioid peptide/receptor systems play a central role in the addictive states and therefore in their treatment. (2) That atypical responsivity to stressors (e.g., in the hypothalamic-pituitary-adrenal axis) plays a role in vulnerability and relapse to specific addictive diseases. This atypical responsivity may be drug-induced, environmentally acquired, and/or due to genetic variation.

Opioids in renal failure and dialysis patients

This article reviews the literature pertaining to the metabolism of several of the commonly used opioids, and the known activity of their metabolites. The effect of renal failure on the pharmacokinetics of these drugs and metabolites is then reviewed. Finally, the effect of renal dialysis on opioid drugs and metabolites is reviewed. Based on the review, it is recommended that morphine and codeine are avoided in renal failure/dialysis patients; hydromorphone or oxycodone are used with caution and close monitoring; and that methadone and fentanyl/sufentanil appear to be safe to use. Note is made that the "safe" drugs in renal failure are also the least dialyzable.

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.

History and current status of opioid maintenance treatments: blending conference session

Opiate addiction is a chronic, relapsing disorder. Left untreated, high morbidity and mortality rates are seen. Pharmacotherapies for this disorder using mu opiate agonists (methadone and levomethadyl acetate) and partial agonists have been developed in the last 40 years. Agonist pharmacotherapy with oral methadone for the treatment of opiate dependence was developed in clinical pharmacology studies at Rockefeller University by Dole, Nyswander, and Kreek. Further studies by this laboratory and others established that moderate to high dose treatment with methadone (80-120 mg) reduced or eliminated opiate use in outpatient settings with consequent reductions in morbidity and up to 4-fold reductions in mortality. Levomethadyl acetate (LAAM), a congener of methadone, is biotransformed to active metabolites responsible for its longer duration of action. The Federal Regulations regarding the dispensation of methadone and LAAM have recently been revised to facilitate the treatment of patients under a "medical maintenance" model. Future regulatory reform will likely involve the establishment of rules for "office based opioid treatment."

Methadone-related opioid agonist pharmacotherapy for heroin addiction. History, recent molecular and neurochemical research and future in mainstream medicine

In 1963, Professor Vincent P. Dole at the Rockefeller University formed a small team to develop a pharmacotherapy for the management of heroin addiction. They hypothesized that heroin addiction is a disease of the brain with behavioral manifestations, and not merely a personality disorder or criminal behavior and began to address the specific question of whether a long-acting opioid agonist could be used in the long-term maintenance treatment of heroin addiction. Over the next 35 years, many studies documented the safety, efficacy and effectiveness of methadone pharmacotherapy for heroin addiction, but Federal regulations and stigmatization of heroin addiction prevented implementation of treatment. Finally, in 1999, NIH published a report unequivocally supporting methadone maintenance pharmacotherapy for heroin addiction. Two other effective opioid agonist treatments have been developed: the even longer acting opioid agonist l-alpha-acetylmethadol (LAAM) has been approved for pharmacotherapy for heroin addiction, and still under study is the opioid partial agonist-antagonist buprenorphine-naloxone combination. A variety of studies, both laboratory based and clinical, have revealed the mechanisms of action of long-acting opioid agonists in treatment, including prevention of disruption of molecular, cellular and physiologic events and, in fact, allowing normalization of those functions disrupted by chronic heroin use. Recent molecular biological studies have revealed single nucleotide polymorphisms of the human mu opioid receptor gene; the mu opioid receptor is the site of action of heroin, the major opiate drug of abuse, analgesic agents such as morphine, and the major treatment agents for heroin addiction. These findings support the early hypotheses of our laboratory that addiction may be due to a combination of genetic, drug-induced and environmental (including behavioral) factors and also, that atypical stress responsivity may contribute to the acquisition and persistence of, as well as relapse to, use of addictive drugs.

Opiate and cocaine addictions: challenge for pharmacotherapies

Neurobiological and behavioral studies, as well as basic and applied clinical research studies, may all contribute to the development of a pharmacotherapy for a specific addictive disease. This paper reviews recent findings from research work, primarily from one laboratory along with collaborative laboratories, that could have some relevance for the development of pharmacotherapy for cocaine dependency. The much earlier experiences of this laboratory in the development of a pharmacotherapy for opiate addiction will be addressed in the context of providing both some specific suggestions for addictive disease pharmacotherapy development and some warnings about the complexities of the introduction and implementation of a pharmacotherapy once developed. Finally, based on both the earlier perspectives and the more recent research findings, some very specific, though speculative, suggestions will be made about the development of novel pharmacotherapies for early opiate addiction, especially for cocaine abuse or addiction and prevention of relapse to cocaine use. The complex and diverse nature of the challenge for pharmacotherapy for the addictive diseases is presented, including specifically a mandate for broadening educational efforts concerning the basis of addictive diseases and the need for treatment, in parallel with the scientific efforts to develop increasingly sophisticated and targeted pharmacotherapies.

Lack of a pharmacologic interaction between rifabutin and methadone in HIV-infected former injecting drug users

Rifampin, an agent known to decrease the half-life of methadone, and rifabutin are two rifamycins that are structurally similar and share mechanisms of action. Hence the possibility of a drug-drug interaction between rifabutin and methadone was evaluated in 24 methadone-maintained, former injecting drug users infected with the human immunodeficiency virus. The study was an open-label, drug-drug interaction and safety trial in which patients were followed for 15 days. Each patient received rifabutin 300 mg as a single dose concomitantly with their individualized methadone dosage. No significant differences in methadone peak plasma concentration, time to peak plasma concentration, area under the plasma concentration-time curve, systemic clearance or renal clearance was observed in the presence of rifabutin. Seventy-five percent of the patients reported at least one symptom of narcotic withdrawal during the study, however, these symptoms were mild. A relationship between the development of narcotic withdrawal and methadone systemic exposure could not be established. Concurrent administration of rifabutin and methadone appeared to be safe in human immunodeficiency virus-infected injecting drug users maintained on stable doses of methadone and is not expected to produce any significant changes in the pharmacokinetics of methadone in these patients.

Opioid receptors: some perspectives from early studies of their role in normal physiology, stress responsivity, and in specific addictive diseases

The early history of research on the possible existence of specific opioid receptors and on developing a new form of pharmacotherapy for the treatment of heroin addiction in New York City, from 1960-1973, along with the special relationships between two leading scientists conducting these research efforts, Dr. Eric Simon and Dr. Vincent P. Dole Jr., are presented in a historical perspective. The linkage of these early efforts and the subsequent identification and the elucidation of the effects of exogenous opiates acting at specific opiate receptors in human physiology, including some findings from perspective studies of heroin addicts at time of entry to and during methadone maintenance treatment, are presented in the context of the important clues which thereby were provided concerning the possible roles of the endogenous opioids in normal mammalian physiology. From many of these early clinical research findings and studies in animal models, the hypothesis that the endogenous opioids system may play an important role in stress responsivity was formulated along with the related hypothesis, first presented in the early 1970s, that an atypical responsivity to stress and stressors might be involved in the acquisition and persistence of, and relapse to specific addictive diseases, including heroin addiction, cocaine dependency and alcoholism. More recent studies of the possible involvement of the specific opioid receptors in these three addictive diseases-heroin addiction, cocaine addiction and alcoholism-from our laboratory are discussed in a historical perspective of the development of these ideas from the early research findings of not only Dr. Eric Simon, but his numerous colleagues in opioid research in the United States and throughout the world.

Methadone in the management of cancer pain: a review

Methadone is a synthetic opiate receptor agonist that has been available for more than 40 years. Although its main use has been in the maintenance treatment of opioid addicts, it has excellent analgesic effects and low cost. Its use is limited by its long and unpredictable half-life and by the limited knowledge of the most appropriate method for titration and interval of administration. Most reports on this drug are uncontrolled and limited to a small number of patients receiving low doses of methadone. Methadone should be titrated carefully and individualized doses and intervals should be determined for each patient. Future research should attempt to determine the equi-analgesic dose for chronic use, its effectiveness and tolerance when used in high doses, and its absorption and tolerance using alternative routes, e.g., rectal and subcutaneous.

Stereoselective determination of the enantiomers of methadone in plasma using high-performance liquid chromatography

An enantioselective high-performance liquid chromatographic assay for the quantification of methadone in human and beagle plasma is described. The procedure involves extraction of methadone from alkalized plasma into hexane-isoamyl alcohol (99:1, v/v). Stereoselective separation was achieved with a silica column with covalently bound alpha 1-acid glycoprotein (Chiral-AGP) without any derivatization procedure. The detection wavelength was set at 215 nm. Using an internal standard provided reliable control of the extraction procedure as well as quantification of the enantiomers of methadone. The limit of quantification was found to be 2.5 ng/ml. The method was demonstrated to be sufficiently sensitive for stereoselective pharmacokinetic studies of methadone.

The use of plasma levels to optimize methadone maintenance treatment

The question of the optimal methadone dose during maintenance therapy is controversial. For both philosophical and practical reasons, therapeutic drug monitoring has not been generally used. Some therapists prescribe low doses of methadone more for psychological than pharmacological reasons. This study examines, in 104 methadone patients, the relation between self-rating, observer-rating, urine tests, HIV-1 sero-status, daily methadone doses and plasma levels of methadone. No differences were found between HIV-1 infected and seronegative patients in these respects. The optimal methadone plasma level as judged by self- and observer-rating was more than 150 ng/ml. For oral methadone, the best results are obtained in patients receiving more than 90 mg daily. We found a significant relationship between methadone dose and plasma levels, also in patients who also used illicit drugs. We conclude that therapeutic drug monitoring should become routine in methadone treatment to achieve optimum results, especially in patients who complain of withdrawal symptoms and continue high-risk behaviour.

Psychophysiological reactions in methadone maintenance patients do not correlate with methadone plasma levels

In methadone maintenance therapy methadone plasma concentrations of 400 ng/ml are necessary to suppress any further opiate action and to provide stabilized maintenance. In a controlled study we have searched for a differentiation in autonomous activation between patients having low and high methadone plasma levels, using static and dynamic pupillometry and habituation of skin conductance response. Results show that there is no difference in psychophysiological response between patients with high (greater than 400 ng/ml) or low (less than 400 ng/ml) plasma levels of methadone. This indicates that there is no reduction in behavioral arousal in patients with high plasma methadone levels. On the basis of these findings, there is no rationale to maintain patients on plasma levels below 400 ng/ml.

Substance abuse treatment modalities in the age of HIV spectrum disease

AMSAODD's Third National Forum on AIDS and Chemical Dependency presented a session about the theory and practicality of combining pharmacologic and nonpharmacologic treatment modalities to maximize the social, psychological, and physical health of patients. Synthesizing methadone maintenance for opioid dependence with abstinence modalities for cocaine dependence and alcoholism was discussed. Chronic adequate methadone treatment allows normalization of neuroendocrine function, is associated with normal natural killer-cell activity, and has proven efficacious in retaining patients in chemical dependence treatment, and thus decreasing the risk for transmission of HIV infection. Individualization of treatment is then exemplified by four clinical vignettes that were discussed by a panel of experts.

Effect of severe alcoholic liver disease on the disposition of methadone in maintenance patients

We studied methadone disposition in 11 maintenance patients with alcoholic liver disease of such severity that liver biopsy was contraindicated. Nine methadone-maintained patients with recent alcohol abuse but minimal or no evidence of liver disease served as controls. Most kinetic indices, including the apparent oral clearance and area under the concentration-time curves, were similar in patients and controls. Although the apparent terminal half-life of methadone was longer (p = 0.04) in the patients with liver disease, the peak plasma methadone level was lower (p = 0.03). None of the patients had signs or symptoms of methadone overdosage or abstinence at the time of study. Six patients and one control had flattened plasma methadone concentration-time curves. We hypothesize that, in severe liver disease, damage to hepatic drug-metabolizing systems is offset by damage to the capacity of the liver to store and release unchanged methadone. The usual methadone maintenance dose may be continued in stable patients with severe alcoholic cirrhosis.

Circadian rhythms and levels of beta-endorphin, ACTH, and cortisol during chronic methadone maintenance treatment in humans

Previous studies have shown alterations of neuroendocrine function in humans receiving any narcotic on short-term basis or short-acting narcotics on a chronic basis. In this study of 16 well-stabilized patients, it was demonstrated that normalization of hypothalamic-pituitary-adrenal axis function, as reflected by normal levels and normal circadian rhythm of levels of beta-endorphin, ACTH and cortisol, is achieved during long-term steady state methadone maintenance treatment of former heroin addicts.

Quantitation of methadone enantiomers in humans using stable isotope-labeled [2H3]-, [2H5]-, and [2H8]Methadone

A new technique for simultaneous stereoselective kinetic studies of methadone enantiomers was developed using three deuterium-labeled forms of methadone and GLC-chemical-ionization mass spectrometry. A racemic mixture (1:1) of (R)-(-)-[2H5]methadone (l-form) and (S)-(R)-[2H3]methadone (d-form) was administered orally in place of a single daily dose of unlabeled (+/-)-[2H0]methadone in long-term maintenance patients. Racemic (+/-)-[2H8]methadone was used as an internal standard for the simultaneous quantitation of [2H0]-, [2H3]-, and [2H5]methadone in plasma and urine. A newly developed extraction procedure, using a short, disposable C18 reversed-phase cartridge and improved chemical-ionization procedures employing ammonia gas, resulted in significant reduction of the background impurities contributing to the ions used for isotopic abundance measurements. These improvements enabled the measurement of labeled plasma methadone levels for 120 hr following a single dose. This methodology was applied to the study of methadone kinetics in two patients; in both patients, the analgesically active l-enantiomer of the drug had a longer plasma elimination half-life and a smaller area under the plasma disappearance curve than did the inactive d-form.

Acute effects of ethanol on hepatic uptake and distribution of narcotics in the isolated perfused rabbit liver

This study was performed as an initial step in systematically defining the hepatic interactions between ethanol and opioids using a controlled in vitro system. The acute effects of ethanol on the initial uptake and distribution of long- and short-acting narcotics were studied using isolated rabbit liver perfused with rabbit blood without or with ethanol. A pulse injection of 1.5 mg of 14C-labeled narcotic [methadone, 1-alpha-acetylmethadol (LAAM), morphine, or meperidine] was made into the portal vein cannula followed by perfusion for 2 min. Radioactivity was determined in liver homogenates and subcellular fractions; methadone and its metabolites were measured by thin-layer chromatography with zonal scanning in each fraction. Ethanol preperfusion and concomitant ethanol perfusion did not effect hepatic uptake of methadone, LAAM, morphine, or meperidine. Although subcellular localization of morphine and meperidine differed from that of methadone and LAAM, perfusion with ethanol did not alter the acute hepatic uptake and distribution of any of the narcotics. These findings suggest that acute exposure to ethanol does not alter the acute hepatic disposition of narcotics.

Metabolic interactions between opiates and alcohol

1. Acute preperfusion with ethanol does not alter significantly the initial hepatic extraction or subcellular distribution of narcotics, or the immediate biotransformation of the long-acting narcotic, methadone, using the isolated perfused rabbit liver. However, the acute administration of ethanol may alter distribution and/or impair hepatic drug metabolism in perfusion studies of longer duration, or in vivo, as has been suggested by others in studies of several drugs. 2. Following chronic treatment with both ethanol and methadone in the rat, plasma levels of unmetabolized methadone, determined by gas liquid chromatography, are significantly lowered. 3. Following chronic treatment with methadone alone, blood elimination rates of ethanol are accelerated to a greater extent than following chronic treatment with ethanol alone in the rat; following chronic treatment with both methadone and ethanol, rates of ethanol elimination are accelerated to a significantly more rapid rate than following treatment with either agent alone. 4. To date, clinical studies in patients on chronic steady-dose methadone maintenance treatment, without liver disease, polydrug abuse, or heavy use of ethanol, show no significant acute dispositional interactions between methadone and ethanol. 5. Clinical studies in patients on chronic steady-dose methadone maintenance treatment, without liver disease, polydrug abuse, or heavy use of ethanol, show no significant dispositional interactions between methadone and disulfiram (Antabuse) when the latter was given for one week for study purposes only. 6. Clinical studies of possible dispositional interactions between methadone and ethanol in methadone-maintained patients, who are also chronic abusers of alcohol, are now in progress.

Effects of liver disease on urinary excretion of methadone and metabolites in maintenance patients: quantitation by direct probe chemical ionization mass spectrometry

This study was performed to define the amounts of methadone and metabolites excreted in urine in otherwise healthy maintenance patients, and to determine whether the metabolism and elimination of methadone, as assessed by analyses of urines, is altered in patients with liver disease. A method was developed for the simultaneous quantitation of methadone and six of its major and minor metabolites using chemical ionization mass spectrometry with direct probe introduction to increase sensitivity for analyses of the minor metabolites. Analyses of urine from unmedicated volunteers showed that the interferences at the mass range of interest (264-326) were usually small and therefore would not introduce significant error into analysis. Nineteen patients well-stabilized in chronic long-term methadone treatment were studied, five otherwise healthy males and fourteen patients with chronic liver disease (nine males and four females). Twenty-four hour urine collections were made and analyzed following extraction procedures. The concentrations of methadone and the major pyrrolidine metabolite exceeded 1 microgram ml-1 in all cases; the concentration (listed in descending order) of pyrrolidone, pyrroline, hydroxymethadone, hydroxypyrroline, methadol and hydroxypyrrolidine were all less than 1 microgram ml-1. The total 24 hour urinary excretion of methadone and its metabolites was 48.3% (+/- 1.71 SEM) in otherwise healthy patients but was significantly lower, 32.6% (+/- 3.19 SEM) in patients with liver disease (p less than 0.05). The total 24 hour excretion of the pyrrolidone metabolite, the end product of two pathways of methadone metabolism, was also significantly reduced in patients with liver disease (p less than 0.05). Females with liver disease had significantly higher ratios of pyrrolidine to methadone than did males with liver disease (p less than 0.05).

Methadone-disulfiram interaction during methadone maintenance

In an attempt to characterize a possible drug interaction between methadone and disulfiram, 500 mg/day insulfiram was administered orally for seven days to seven subjects on methadone maintenance. Plasma methadone concentrations and urinary excretion of methadone and its pyrrolidine and pyrrolidone metabolites were measured and subjective symptoms of opiate intoxication and abstinence were noted before, during, and after disulfiram administration. Mean trough plasma methadone concentrations and terminal half-lives were lowest and shortest during disulfiram treatment, although this finding was not statistically significant. The ratio of urinary methadone to its pyrrolidine metabolite decreased during disulfiram treatment in all subjects. There is no evidence to support our original hypothesis that disulfiram might inhibit methadone metabolism. In contrast, urinary excretion of the major pyrrolidine metabolite increased relative to excretion of methadone. This suggests enhanced N-demethylation during disulfiram treatment. Disulfiram had no effect on opiate intoxication or abstinence symptoms. Disulfiram may alter methadone disposition, but in this study it was shown that in doses used for management of alcoholism there was no significant interaction between disulfiram and methadone.

Methadone use in patients with chronic renal disease

Methadone disposition was studied in three patients receiving chronic methadone treatment and having chronic renal disease: one oliguric patient during peritoneal dialysis, one anuric patient on hemodialysis, and one patient following renal transplantation. In all three patients plasma levels of methadone remained within the desired therapeutic range (0.09--0.68 microgram/ml) for the doses received (40-50 mg/day). Elimination of methadone and its metabolites was almost exclusively by the fecal route in the anuric patient. Less than 1% of the daily dose was removed by peritoneal dialysis or hemodialysis. There was no laboratory or clinical evidence for accumulation of either methadone or its metabolites, suggesting that methadone is an appropriate narcotic to use in patients with renal disease.

Lethal synergism between morphine or other narcotic analgesics and propranolol

Interactions of (+/-)-propranolol HCl with various narcotics were determined in albino rats. The 24-h intraperitoneal (i.p.) LD50 of morphine sulfate + saline was 15--16 times greater than for morphine + propranolol in both sexes although morphine was nearly twice as toxic to males as to females. The potency ratios for LD50's with saline vs. with propranolol were: codeine, 1.9, (+/-)-methadone, 6.0; (-)-alpha-acetylmethadol, 2.8 (72 h). The toxicity of levorphanol also was greatly increased with propranolol, but the dose-effect relationship showed non-parallelism vs. levorphanol + saline. Albino mice and mongrel dogs also showed synergism between morphine and propranolol. Mortality after morphine and propranolol was antagonized by naloxone or naltrexone in rats and mice. The potency ratio in rats for morphine + saline vs. morphine + practolol was 3.5. However, the synergism between propranolol and the narcotics probably was unrelated to beta-adrenergic blocking effects of propranolol because of the apparent equivalence of (+)-, (-)- and (+/-)-propranolol in rats for synergism with morphine.

[OH]- negative chemical ionization mass spectrometry. Reactions of [OH]- with methadone, l-alpha-acetylmethadol and their metabolites

The [OH]- chemical ionization spectra of methadone and three metabolites and of l-alpha-methadol and six metabolites are presented. The spectra are simple, but the methadol compounds exhibit much fragmentation. The ionization sensitivity is somewhat greater than that in CH4 positive chemical ionization.

Behavioral supersensitivity to apomorphine following chronic narcotic treatment in the guinea pig

Male albino guinea pigs were treated for 3 weeks with methadone, morphine, haloperidol, or saline. One week and 5 weeks following termination of treatment they were challenged with the directly acting dopaminergic agonist apomorphine. At the week 1 test the haloperidol and saline groups did not differ, but behavioral supersensitivity was apparent in significantly elevated mean stereotypy scores of the methadone and morphine groups relative to the saline group. The source of differences in mean scores was a higher peak score rather than increased duration of action. At the week 5 test the scores of the methadone group were even higher, the morphine group's scores were equivalent to the saline group's, and the haloperidol group's scores were significant depressed. This study indicates that a 3-week treatment period with methadone or morphine is sufficient to induce dopaminergic supersensitivity and suggests that there may be different time courses for the retention or expression of supersensitivity following these narcotics.

Human spinal fluid methadone levels

Cerebral spinal fluid (CSF) levels of methadone were measured in nine methadone maintenance patients requiring lumbar punctures for medical or surgical treatment. Concurrent serum methadone levels were also determined. The CSF concentration of methadone in all cases was a fraction of the corresponding serum level--ranging from 2 to 73%. The CSF concentrations of methadone ranged from 0.010 to 0.097 ng%. Peak methadone levels in CSF appeared approximately 3 - 8 hours after methadone administration.