Combined in vivo metabolic effects of quetiapine and methadone in brain and blood of rats.

Changes in pharmacokinetics and endogenous metabolites may underlie additive biological effects of concomitant use of antipsychotics and opioids. In this study, we employed untargeted metabolomics analysis and targeted analysis to examine the changes in drug metabolites and endogenous metabolites in the prefrontal cortex (PFC), midbrain, and blood of rats following acute co-administration of quetiapine and methadone. Rats were divided into four groups and received cumulative increasing doses of quetiapine (QTP), methadone (MTD), quetiapine + methadone (QTP + MTD), or vehicle (control). All samples were analyzed using liquid chromatography-mass spectrometry (LC-MS). Our findings revealed increased levels of the quetiapine metabolites: Norquetiapine, O-dealkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide, in the blood and brain when methadone was present. Our study also demonstrated a decrease in methadone and its metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in the rat brain when quetiapine was present. Despite these findings, there were only small differences in the levels of 225-296 measured endogenous metabolites due to co-administration compared to single administrations. For example, N-methylglutamic acid, glutaric acid, p-hydroxyphenyllactic acid, and corticosterone levels were significantly decreased in the brain of rats treated with both compounds. Accumulation of serotonin in the midbrain was additionally observed in the MTD group, but not in the QTP + MTD group. In conclusion, this study in rats suggests a few but important additive metabolic effects when quetiapine and methadone are co-administered.

Distribution of morphine and methadone to the brain in a developmental chicken embryo model.

The use and/or misuse of opioids by pregnant women would expose the fetuses to these drugs during critical stages of development with serious effects for the newborn, like the neonatal abstinence syndrome (NAS). We have revisited an established chicken model for NAS to describe the distribution of morphine and methadone to the brain and explore its validity as a valuable alternative to rodent models. For this purpose, chicken eggs were injected with a single dose of 10 mg/kg or 20 mg/kg morphine or 20 mg/kg methadone onto the chorioallantoic membrane (CAM) on embryonal day 13. Whole brains and lungs were harvested and the concentrations of morphine, methadone and their subsequent metabolites (morphine-3-glucuronide and EDDP, respectively) determined in the brain and lungs at different time points using LC-MS/MS. Morphine and methadone, as well as their metabolites, were detected both in the brain and lungs, with significantly higher concentrations in the lungs. Pharmacokinetic modelling showed that the distribution of morphine to the brain followed a first-order absorption with transit compartments and linear elimination, with concentrations linearly dependent on dose. Moreover, methadone, but not morphine, reduced µ receptor (the main morphine receptor) binding, which can be of relevance for opioid tolerance. The present study is the first to report the brain distribution of morphine, which can be described by standard pharmacokinetic processes, and methadone in the developing chicken embryo. The present findings supplement the already established model and support the use of this chicken model to study NAS.

Chronic exposure to methadone induces activated microglia and astrocyte and cell death in the cerebellum of adult male rats.

Methadone is a centrally-acting synthetic opioid analgesic widely used in the methadone maintenance therapy (MMT) programs throughout the world. Considering its neurotoxic effects particularly on the cerebellum, this study aims to address the behavioral and histological alterations in the cerebellar cortex associated with methadone administration. Twenty-four adult male albino rats were randomized into two groups of control and methadone treatment. Methadone was subcutaneously administered (2.5-10 mg/kg) once a day for two consecutive weeks. The functional and structural changes in the cerebellum were compared to the control group. Our data revealed that treating rats with methadone not only induced cerebellar atrophy, but also prompted the actuation of microgliosis, astrogliosis, and apoptotic biomarkers. We further demonstrated that treating rats with methadone increased complexity of astrocyte processes and decreased complexity of microglia processes. Our result showed that methadone impaired motor coordination and locomotor performance and neuromuscular activity. Additionally, relative gene expression of TNF-α, caspase-3 and RIPK3 increased significantly due to methadone. Our findings suggest that methadone administration has a neurodegenerative effect on the cerebellar cortex via dysregulation of microgliosis, astrogliosis, apoptosis, and neuro-inflammation.

In vitro-in silico-based prediction of inter-individual and inter-ethnic variations in the dose-dependent cardiotoxicity of R- and S-methadone in humans.

New approach methodologies predicting human cardiotoxicity are of interest to support or even replace in vivo-based drug safety testing. The present study presents an in vitro-in silico approach to predict the effect of inter-individual and inter-ethnic kinetic variations in the cardiotoxicity of R- and S-methadone in the Caucasian and the Chinese population. In vitro cardiotoxicity data, and metabolic data obtained from two approaches, using either individual human liver microsomes or recombinant cytochrome P450 enzymes (rCYPs), were integrated with physiologically based kinetic (PBK) models and Monte Carlo simulations to predict inter-individual and inter-ethnic variations in methadone-induced cardiotoxicity. Chemical specific adjustment factors were defined and used to derive dose-response curves for the sensitive individuals. Our simulations indicated that Chinese are more sensitive towards methadone-induced cardiotoxicity with Margin of Safety values being generally two-fold lower than those for Caucasians for both methadone enantiomers. Individual PBK models using microsomes and PBK models using rCYPs combined with Monte Carlo simulations predicted similar inter-individual and inter-ethnic variations in methadone-induced cardiotoxicity. The present study illustrates how inter-individual and inter-ethnic variations in cardiotoxicity can be predicted by combining in vitro toxicity and metabolic data, PBK modelling and Monte Carlo simulations. The novel methodology can be used to enhance cardiac safety evaluations and risk assessment of chemicals.

Time-Dependent Changes in the Serum Levels of Neurobiochemical Factors After Acute Methadone Overdose in Adolescent Male Rat.

Acute methadone toxicity is a major public health concern which has adverse effects on brain tissue and results in recurrent or delayed respiratory arrest. Our study aimed to investigate the time-dependent changes in several serum biochemical markers of brain damage, spatial working memory, and the brain tissue following acute methadone overdose. Adolescent male rats underwent an intraperitoneal (i.p.) injection of 15 mg/kg methadone. In case of apnea occurrence, resuscitation was performed by a ventilatory pump and administrating naloxone (2 mg/kg; i.p.). The animals were classified into groups of treated rats; methadone and naloxone-Apnea (M/N-Apnea), M/N-Sedate, Methadone, Naloxone, and control (saline) groups. The serum levels of S100B, neuron-specific enolase (NSE), myelin basic protein factors, and (Lactate/Pyruvate) L/P ratio were evaluated at the time-points of 6, 24, and 48 h (h). We found that the alterations of S100B and L/P ratio were considerable in the M/N-Apnea and Methadone groups from the early hours post-methadone overdose, while NSE serum levels elevation was observed only in M/N-Apnea group with a delay at 48 h. Further, we assessed the spatial working memory (Y-maze test), morphological changes, and neuronal loss. The impaired spontaneous alternation behavior was detected in the M/N-Apnea groups on days 5 and 10 post-methadone overdose. The morphological changes of neurons and the neuronal loss were detectable in the CA1, striatum, and cerebellum regions, which were pronounced in both M/N-Apnea and Methadone groups. Together, our findings suggest that alterations in the serum levels of S100B and NSE factors as well as L/P ratio could be induced by methadone overdose with the presence or absence of apnea before the memory impairment and tissue injury in adolescent male rats.

Integrating in vitro data and physiologically based kinetic modeling-facilitated reverse dosimetry to predict human cardiotoxicity of methadone.

Development of novel testing strategies to detect adverse human health effects is of interest to replace in vivo-based drug and chemical safety testing. The aim of the present study was to investigate whether physiologically based kinetic (PBK) modeling-facilitated conversion of in vitro toxicity data is an adequate approach to predict in vivo cardiotoxicity in humans. To enable evaluation of predictions made, methadone was selected as the model compound, being a compound for which data on both kinetics and cardiotoxicity in humans are available. A PBK model for methadone in humans was developed and evaluated against available kinetic data presenting an adequate match. Use of the developed PBK model to convert concentration-response curves for the effect of methadone on human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) in the so-called multi electrode array (MEA) assay resulted in predictions for in vivo dose-response curves for methadone-induced cardiotoxicity that matched the available in vivo data. The results also revealed differences in protein plasma binding of methadone to be a potential factor underlying variation between individuals with respect to sensitivity towards the cardiotoxic effects of methadone. The present study provides a proof-of-principle of using PBK modeling-based reverse dosimetry of in vitro data for the prediction of cardiotoxicity in humans, providing a novel testing strategy in cardiac safety studies.

Methadone-induced encephalopathy: a case series and literature review.

BACKGROUND: Accidental ingestion or consumption of supra-therapeutic doses of methadone can result in neurological sequelae in humans. We aimed to determine the neurological deficits of methadone-poisoned patients admitted to a referral poisoning hospital using brain magnetic resonance (MR) and diffusion weighted (DW) imaging. METHODS: In this retrospective study, brain MRIs of the patients admitted to our referral center due to methadone intoxication were reviewed. Methadone intoxication was confirmed based on history, congruent clinical presentation, and confirmatory urine analysis. Each patient had an MRI with Echo planar T1, T2, FLAIR, and DWI and apparent deficient coefficient (ADC) sequences without contrast media. Abnormalities were recorded and categorized based on their anatomic location and sequence. RESULTS: Ten patients with abnormal MRI findings were identified. Eight had acute- and two had delayed-onset encephalopathy. Imaging findings included bilateral confluent or patchy T2 and FLAIR high signal intensity in cerebral white matter, cerebellar involvement, and bilateral occipito-parietal cortex diffusion restriction in DWI. Internal capsule involvement was identified in two patients while abnormality in globus pallidus and head of caudate nuclei were reported in another. Bilateral cerebral symmetrical confluent white matter signal abnormality with sparing of subcortical U-fibers on T2 and FLAIR sequences were observed in both patients with delayed-onset encephalopathy. CONCLUSIONS: Acute- and delayed-onset encephalopathies are two rare adverse events detected in methadone-intoxicated patients. Brain MRI findings can be helpful in detection of methadone-induced encephalopathy.

The Protective and Restorative Effects of Growth Hormone and Insulin-Like Growth Factor-1 on Methadone-Induced Toxicity In Vitro.

Evidence to date suggests that opioids such as methadone may be associated with cognitive impairment. Growth hormone (GH) and insulin-like growth factor-1 (IGF-1) are suggested to be neuroprotective and procognitive in the brain and may therefore counteract these effects. This study aims to explore the protective and restorative effects of GH and IGF-1 in methadone-treated cell cultures. Primary cortical cell cultures were harvested from rat fetuses and grown for seven days in vitro. To examine the protective effects, methadone was co-treated with or without GH or IGF-1 for three consecutive days. To examine the restorative effects, methadone was added for the first 24 h, washed, and later treated with GH or IGF-1 for 48 h. At the end of each experiment, mitochondrial function and membrane integrity were evaluated. The results revealed that GH had protective effects in the membrane integrity assay and that both GH and IGF-1 effectively recovered mitochondrial function and membrane integrity in cells pretreated with methadone. The overall conclusion of the present study is that GH, but not IGF-1, protects primary cortical cells against methadone-induced toxicity, and that both GH and IGF-1 have a restorative effect on cells pretreated with methadone.

Utilizing postmortem drug concentrations in mechanistic modeling and simulation of cardiac effects: a proof of concept study with methadone.

Methadone-related poisoning has been found to be the leading and increasing cause of death among intoxication cases in several countries. Aside from respiratory depression, methadone is known to cause QT-prolongation, which may lead to sudden cardiac death. Concentrations in heart tissue should be more accurate for estimating cardiotoxic effects. The aim of this study was to investigate whether the effect of methadone on the QT-interval could be simulated and whether the concentrations in heart tissues allowed for better prediction of the Bazett corrected QT-interval (QTcB). A predictive performance study was conducted using the simulation platform Cardiac Safety Simulator to mimic five literature studies using their described study conditions. Both free and total plasma and heart concentrations were investigated using two different in silico models: the O'Hara-Rudy (ORD) model and the 10 Tusscher (TNNP) model. The results showed that the QTcB of methadone was best predicted either with total plasma using the TNNP model or with free plasma using the ORD model. The ORD model was highly sensitive to the total heart concentrations, resulting in overprediction of the QTcB. The TNNP model also overpredicted the QTcB, but to a lesser degree than the ORD model. Furthermore, due to a low baseline QTcB, the ORD model underpredicted the QTcB for both the free plasma and free heart concentrations. In conclusion, it is possible to simulate the cardiac effects of methadone, yet several elements influence the approach uncertainty including but not limited to biophysically details model of cardiac electrophysiology, exposure data, and input parameters.

Beneficial effects of co-treatment with dextromethorphan on prenatally methadone-exposed offspring.

BACKGROUND: Heroin use among young women of reproductive age has drawn much attention around the world. Although methadone is widely used in maintenance therapy for heroin/morphine addiction, the long-term effects of prenatal exposure to methadone and preventative therapy remain unclear. For revealing this question, female pregnant Sprague-Dawley rats were sub-grouped to receive (1) vehicle, (2) methadone 5 mg/kg at embryonic day 3 (E3) and then 7 mg/kg from E4 to E20, (3) dextromethorphan (DM) 3 mg/kg, and (4) methadone + DM (the rats received methadone followed by DM treatment), subcutaneously, twice a day from E3 to E20. The body weight, natural withdrawal, pain sensitivity, ED50, conditioned place preference and water maze were conducted at different postnatal stages (P1 to P79) of offspring. The quantitative real-time RT-PCR and electrophysiology were also used to measure the gene expression of opioid receptors in the spinal cord and changes of LTP/LTD in the hippocampus, separately. RESULTS: Prenatal exposure to methadone or DM did not affect survival rate, body weight, water maze and LTP or LTD of offspring. However, prenatal methadone significantly increased the withdrawal symptoms, pain sensitivity, addiction liability and decreased the mRNA expression of pain related opioid receptors. Co-administration of DM with methadone in the maternal rats effectively prevented these abnormalities of offspring induced by methadone. CONCLUSIONS: Our study clearly showed that co-administration of dextromethorphan with methadone in the maternal rats prevented the adverse effects induced by prenatal methadone exposure. It implies that dextromethorphan may have a potential to be used in combination with methadone for maintenance treatment in pregnant heroin-addicted women to prevent the adverse effects induced by methadone on offspring.

Hyperalgesia and increased sevoflurane minimum alveolar concentration induced by opioids in the rat: a randomised experimental study.

BACKGROUND: Perioperative opioids reduce inhalational anaesthetic requirements. The initial hypoalgesia may, however, be followed by a rebound hyperalgesia. OBJECTIVES: To determine whether prior opioid administration influences inhalational anaesthetic requirements, which might be associated with opioid-induced hyperalgesia. DESIGN: A prospective, randomised, experimental study. SETTING: Experimental Surgery, La Paz University Hospital, Madrid, Spain. ANIMALS: Seventy-nine adult male Wistar rats. INTERVENTIONS: Sevoflurane minimum alveolar concentration (MAC) and mechanical nociceptive thresholds (MNTs) were assessed at baseline and 7 days later following opioid treatment with remifentanil 120 µg  kg-1  h-1, buprenorphine 150 µg kg-1, methadone 8 mg  kg-1 or morphine 10 mg  kg-1 The duration of the effect of remifentanil on MAC and MNT was evaluated in addition to the preventive effect of ketamine 10 mg  kg-1 on remifentanil-induced hyperalgesia. MAIN OUTCOME MEASURES: The effect of different opioid treatments on MAC and MNT was evaluated using analysis of variance (ANOVA). RESULTS: All studied opioids produced an immediate reduction in sevoflurane MAC, followed by an increase (16%) in baseline MAC 7 days later (P < 0.05), although the immediate MAC reduction produced by these opioids at that time was not different. Remifentanil produced a decrease in MNT (P < 0.05), which was associated with an increase in the MAC (P < 0.05) that persisted at 21 days. The effect of remifentanil on MNT and MAC was blocked by ketamine. CONCLUSION: Opioid-induced hyperalgesia was associated with an increase in the MAC in normal rats who had not undergone surgery. Both effects lasted 21 days and were prevented by ketamine.

Problem based review: The patient taking methadone.

Methadone maintenance treatment (MMT) is an effective therapy for opioid-dependence; its use is based on a harm reduction philosophy and represents one of a range of treatment approaches for opioid-dependent individuals. The medical literature supports MMT as a well established and cost-effective treatment for opioid-dependence that allows a return-to-normal physiological, psychological and societal functioning. The effectiveness of MMT is enhanced by psycho-social interventions such as contingency management and addressing other co-existing health and social needs. MMT saves lives and reduces violent and non-violent crime, drug use and the transmission of HIV, hepatitis C and other communicable diseases. For some people, MMT may continue for life, while others may eventually be able to discontinue and remain abstinent. Methadone interacts with numerous drugs and prolongs the corrected QT interval (QTc) with risk of sudden cardiac death. It has a prolonged half-life and premature discharge of patients after methadone overdose may be fatal. Each patient must be assessed, treated and monitored on an individual basis. Successful outcomes through MMT require knowledge, experience, vigilance, and diligence on the part of the physician, the patient and all of those involved in treatment.

[Review of cases of prolonged QTC and wave burst arrhythmia in patients treated with methadone]. / Revue des cas d'allongements du QTC et de torsades de pointe chez des patients traités par méthadone.

INTRODUCTION: For the past 40 years, methadone has been known to be an efficient treatment of substitution. Its use allowed a significant reduction in the mortality related to opioid addiction. Since 2001, many articles have reported some cases of syncope, wave burst arrhythmia, ventricular tachycardia due to prolonged QT interval and sudden death secondary to cardiac arrest, with a risk of prolongation of the QT interval above 440 ms (men) and 460 ms (women). Many explorations have helped in understanding the physiopathology by showing that opioids, including methadone, cause a blockage of the potassium channels of the gene HERG K+P. This event could slow the repolarisation and the atrioventricular cardiac synchronization and could induce ventricular arrhythmia. LITERATURE FINDINGS: Nearly 20 studies showed a prolonged QT interval secondary to methadone in patients exhibiting the following features: (1) patients with cardiac pathologies, notably bradycardia, congenital long QT interval, myocardial pathologies related to AIDS and electrolyte disturbances; (2) patients receiving concomitant treatment with substances known to prolong QT interval, such as psychoactive stimulants, narcoleptics, tricyclic antidepressants, antiarrhythmic agents, macrolids, quinolones, non diuretic hypokalemiants and certain corticoids; (3) patients receiving treatments that inhibit methadone's metabolism, particularly those that act on the cytochrome P450 3A4 such as SSRI, antifungal agents, some macrolids and some retroviral agents. Many recent studies, while evaluating the dose-dependent effect of methadone on the QT prolongation, showed a tendency to a prolonged QT when using higher doses of methadone. CONCLUSION: Screening for these risk factors should be carried out before prescribing methadone. EKG should not be systematically performed unless the conditions described above are present or if a higher dose of methadone is needed.

Is high sensitive-troponin I a reliable biomarker for cardiac injury in methadone toxicity? A prospective cross-sectional study.

BACKGROUND: Methadone is a synthetic opioid mostly used for detoxification therapy, as its use increases; the possibility for methadone-induced cardiotoxicity may rise. The aim of this study was to determine the association of high-sensitivity troponin I levels as a predictor of cardiac injury in methadone toxicity. METHODS: Sixty methadone toxicity patients included in this prospective cross-sectional study from October 2018-November 2020. High-sensitivity troponin I level and electrocardiogram were assessed in patients at admission. All patients underwent echocardiography at admission and 30 days later and compared this finding between two groups based on high-sensitivity troponin I results. RESULTS: Mean age of the patients was 34.5 ± 11.1 years (males: 67%). Twenty (20%) patients had positive high sensitive-troponin results. Long QT interval and inverted T in precordial leads were mostly observed in individuals with positive high-sensitivity troponin I (75% vs. 35%, P = 0.013 and 83% vs. 16%, P < 0.001, respectively). Patients with elevated troponin had reduced left ventricular ejection fraction in comparison to normal group during admission (43.1 ± 15.4% vs. 55%, P < 0.001) and this left ventricular ejection fraction remained abnormal after 30 days (43.7 ± 21.6%). Patients in positive high-sensitivity troponin I group had higher regional wall motion abnormality frequency both at admission and 30 days later compared to the other group (0 day: 42% vs. 0, P < 0.001, 30th days: 25% vs. 4%, P = 0.020). CONCLUSION: Patients with simultaneous methadone toxicity and positive high-sensitivity troponin I had worse cardiac outcomes and this biomarker could be probably used for better implementation of therapeutic interventions and prognosis.

Chronic exposure to methadone impairs memory, induces microgliosis, astrogliosis and neuroinflammation in the hippocampus of adult male rats.

Methadone is a centrally-acting synthetic opioid analgesic widely used in methadone maintenance therapy (MMT) programs throughout the world. Given its neurotoxic effects, particularly on the hippocampus, this study aims to address the behavioral and histological alterations in the hippocampus associated with methadone administration. To do so, twenty-four adult male albino rats were randomized into two groups, methadone treatment and control. Methadone was administered subcutaneously (2.5-10 mg/kg) once a day for two consecutive weeks. A comparison was drawn with behavioral and structural changes recorded in the control group. The results showed that methadone administration interrupted spatial learning and memory function. Accordingly, treating rats with methadone not only induced cell death but also prompted the actuation of microgliosis, astrogliosis, and apoptotic biomarkers. Furthermore, the results demonstrated that treating rats with methadone decreased the complexity of astrocyte processes and the complexity of microglia processes. These findings suggest that methadone altered the special distribution of neurons. Also, a substantial increase was observed in the expression of TNF-α due to methadone. According to the findings, methadone administration exerts a neurodegenerative effect on the hippocampus via dysregulation of microgliosis, astrogliosis, apoptosis, and neuro-inflammation.

CYP2B6 and OPRM1 gene variations predict methadone-related deaths.

The largest proportion of methadone-associated deaths occurs during the drug induction phase. We analysed methadone-related fatalities for gene variations linked with methadone action. A significant association between high methadone concentrations and the CYP2B6*6 allele characteristic of the slow metabolizer phenotype was identified. We suggest that the risk of methadone fatality may be predetermined in part by the CYP2B6*6 allele. A significant correlation was also observed between post-mortem benzodiazepine concentrations and the OPRM1 A118G allele GA in methadone-related fatalities. Screening for these susceptibility variations prior to methadone prescription could assist in reducing the potential for serious adverse effects.

Enhancement of tolerance development to morphine in rats prenatally exposed to morphine, methadone, and buprenorphine.

BACKGROUND: Abuse of addictive substances is a serious problem that has a significant impact on areas such as health, the economy, and public safety. Heroin use among young women of reproductive age has drawn much attention around the world. However, there is a lack of information on effects of prenatal exposure to opioids on their offspring. In this study, an animal model was established to study effects of prenatal exposure to opioids on offspring. METHODS: Female pregnant Sprague-Dawley rats were sub-grouped to receive (1) vehicle, (2) 2-4 mg/kg morphine (1 mg/kg increment per week), (3) 7 mg/kg methadone, and (4) 3 mg/kg buprenorphine, subcutaneously, once or twice a day from E3 to E20. The experiments were conducted on animals 8-12 weeks old and with body weight between 250 and 350 g. RESULTS: Results showed that prenatal exposure to buprenorphine caused higher mortality than other tested substance groups. Although we observed a significantly lower increase in body weight in all of the opioid-administered dams, the birth weight of the offspring was not altered in all treated groups. Moreover, no obvious behavioral abnormality or body-weight difference was noted during the growing period (8-12 weeks) in all offspring. When the male offspring received morphine injection twice a day for 4 days, the prenatally opioid-exposed rats more quickly developed a tolerance to morphine (as shown by the tail-flick tests), most notably the prenatally buprenorphine-exposed offspring. However, the tolerance development to methadone or buprenorphine was not different in offspring exposed prenatally to methadone or buprenorphine, respectively, when compared with that of the vehicle controlled group. Similar results were also obtained in the female animals. CONCLUSIONS: Animals prenatally exposed to morphine, methadone, or buprenorphine developed tolerance to morphine faster than their controlled mates. In our animal model, prenatal exposure to buprenorphine also resulted in higher mortality and much less sensitivity to morphine-induced antinociception than prenatal exposure to morphine or methadone. This indicates that buprenorphine in higher doses may not be an ideal maintenance drug for treating pregnant women. This study provides a reference in selecting doses for clinical usage in treating pregnant heroin addicts.

Mechanisms of respiratory insufficiency induced by methadone overdose in rats.

Methadone may cause respiratory depression. We aimed to understand methadone-related effects on ventilation as well as each opioid-receptor (OR) role. We studied the respiratory effects of intraperitoneal methadone at 1.5, 5, and 15 mg/kg (corresponding to 80% of the lethal dose-50%) in rats using arterial blood gases and plethysmography. OR antagonists, including intravenous 10 mg/kg-naloxonazine at 5 minutes (mu-OR antagonist), subcutaneous 30 mg/kg-naloxonazine at 24 hours (micro1-OR antagonist), 3 mg/kg-naltrindole at 45 minutes (delta-OR antagonist) and 5 mg/kg-Nor-binaltorphimine at 6 hours (kappa-OR antagonist) were pre-administered. Plasma concentrations of methadone enantiomers were measured using high-performance liquid chromatography coupled to mass-spectrometry. Methadone dose-dependent inspiratory time (T(I)) increase tended to be linear. Respiratory depression was observed only at 15 mg/kg and characterized by an increase in expiratory time (T(E)) resulting in hypoxemia and respiratory acidosis. Intravenous naloxonazine completely reversed all methadone-related effects on ventilation, while subcutaneous naloxonazine reduced its effects on pH (P < 0.05), PaCO(2) (P < 0.01) and T(E) (P < 0.001) but only partially on T(I) (P < 0.001). Naltrindole reduced methadone-related effects on T(E) (P < 0.001). Nor-binaltorphimine increased methadone-related effects on pH and PaO(2) (P < 0.05) Respiratory effects as a function of plasma R-methadone concentrations showed a decrease in PaO(2) (EC(50): 1.14 microg/ml) at lower concentrations than those necessary for PaCO(2) increase (EC(50): 3.35 microg/ml). Similarly, increased T(I) (EC(50): 0.501 microg/ml) was obtained at lower concentrations than those for T(E) (EC(50): 4.83 microg/ml). Methadone-induced hypoxemia is caused by mu-ORs and modulated by kappa-ORs. Additionally, methadone-induced increase in T(E) is caused by mu1- and delta-opioid receptors while increase in T(I) is caused by mu-ORs.

ABCB1, CYP2B6, and CYP3A4 genetic polymorphisms do not affect methadone maintenance treatment in HCV-positive patients.

The aim of this study was to determine the influence of ABCB1, CYP2B6, and CYP3A4 genetic polymorphisms on methadone metabolism in patients with hepatitis C virus (HCV) undergoing methadone maintenance treatment (MMT). The study included 35 participants undergoing MMT, who were divided in three groups: HCV-positive (N=12), HCV-negative (N=16), and HCV clinical remission (CR) (N=7). The concentrations of methadone and its main metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) were determined with gas chromatography-mass spectrometry. The patients were genotyped for ABCB1 rs1045642, CYP2B6 rs3745274, CYP3A4 rs2242480, and CYP3A4 rs2740574 polymorphisms. Differences between single nucleotide polymorphism (SNP) genotypes and methadone-to-EDDP ratio were analysed with one-way ANOVA, which showed no significant difference between the genes (p=0.3772 for ABCB1 rs1045642, p=0.6909 for CYP2B6 rs3745274, and p=0.6533 for CYP3A4 rs2242480). None of the four analysed SNP genotypes correlated with methadone-to-EDDP concentration ratio. A major influence on it in hepatitis C-positive patients turned out to be the stage of liver damage.