A Novel Perioperative Multidose Methadone-Based Multimodal Analgesic Strategy in Children Achieved Safe and Low Analgesic Blood Methadone Levels Enabling Opioid-Sparing Sustained Analgesia With Minimal Adverse Effects.

BACKGROUND: Intraoperative methadone, a long-acting opioid, is increasingly used for postoperative analgesia, although the optimal methadone dosing strategy in children is still unknown. The use of a single large dose of intraoperative methadone is controversial due to inconsistent reductions in total opioid use in children and adverse effects. We recently demonstrated that small, repeated doses of methadone intraoperatively and postoperatively provided sustained analgesia and reduced opioid use without respiratory depression. The aim of this study was to characterize pharmacokinetics, efficacy, and safety of a multiple small-dose methadone strategy. METHODS: Adolescents undergoing posterior spinal fusion (PSF) for idiopathic scoliosis or pectus excavatum (PE) repair received methadone intraoperatively (0.1 mg/kg, maximum 5 mg) and postoperatively every 12 hours for 3-5 doses in a multimodal analgesic protocol. Blood samples were collected up to 72 hours postoperatively and analyzed for R-methadone and S-methadone, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidene (EDDP) metabolites, and alpha-1 acid glycoprotein (AAG), the primary methadone-binding protein. Peak and trough concentrations of enantiomers, total methadone, and AAG levels were correlated with clinical outcomes including pain scores, postoperative nausea and vomiting (PONV), respiratory depression, and QT interval prolongation. RESULTS: The study population included 38 children (10.8-17.9 years): 25 PSF and 13 PE patients. Median total methadone peak plasma concentration was 24.7 (interquartile range [IQR], 19.2-40.8) ng/mL and the median trough was 4.09 (IQR, 2.74-6.4) ng/mL. AAG concentration almost doubled at 48 hours after surgery (median = 193.9, IQR = 86.3-279.5 µg/mL) from intraoperative levels (median = 87.4, IQR = 70.6-115.8 µg/mL; P < .001), and change of AAG from intraoperative period to 48 hours postoperatively correlated with R-EDDP (P < .001) levels, S-EDDP (P < .001) levels, and pain scores (P = .008). Median opioid usage was minimal, 0.66 (IQR, 0.59-0.75) mg/kg morphine equivalents/d. No respiratory depression (95% Wilson binomial confidence, 0-0.09) or clinically significant QT prolongation (median = 9, IQR = -10 to 28 milliseconds) occurred. PONV occurred in 12 patients and was correlated with morphine equivalent dose (P = .005). CONCLUSIONS: Novel multiple small perioperative methadone doses resulted in safe and lower blood methadone levels, <100 ng/mL, a threshold previously associated with respiratory depression. This methadone dosing in a multimodal regimen resulted in lower blood methadone analgesia concentrations than the historically described minimum analgesic concentrations of methadone from an era before multimodal postoperative analgesia without postoperative respiratory depression and prolonged corrected QT (QTc). Larger studies are needed to further study the safety and efficacy of this methadone dosing strategy.

Stereoselective Analysis of Methadone and EDDP in Laboring Women and Neonates in Plasma and Dried Blood Spots and Association with Neonatal Abstinence Syndrome.

OBJECTIVE: This pilot study evaluated the relationship between maternal and neonatal R- and S-methadone and R- and S-2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) exposure and the severity of neonatal abstinence syndrome (NAS). The use of dried blood spots (DBS) as an alternative for plasma in assessing methadone and EDDP was also assessed. STUDY DESIGN: Women receiving methadone for medication assisted treatment of opioid use disorder during pregnancy were eligible for recruitment. Plasma and DBS samples were collected from mothers during labor, from cord blood, and from newborns during genetic screen. R-/S-methadone and EDDP were measured by high-performance liquid chromatography tandem mass spectrometry (HPLC/MS/MS). Associations between methadone exposure, neonatal morphine requirements, and severity of NAS were examined. RESULTS: Twenty women and infants completed the study. Maternal methadone dose at delivery was 112 mg/day (range = 60-180 mg/day). Sixteen neonates experienced NAS requiring morphine; three also required phenobarbital. Higher cord blood concentrations of R-methadone, R- and S-EDDP were associated with higher maximum doses of morphine (p < 0.05). CONCLUSION: Maternal methadone and cord blood concentration at delivery are variable and may be potential markers of neonatal abstinence syndrome.

Review of LC techniques for determination of methadone and its metabolite in the biological samples.

Methadone (MTD) is a synthetic analgesic drug used for treating opioid dependence and effectively used clinically for patients with severe pain. The abuse of MTD may lead to poisoning, disorder in the central nervous system and even death. The regular monitoring of MTD in biological matrices including serum, plasma and urine samples is an effective way to control abuse of MTD. In this manner, the selection of analytical monitoring of MTD in biological matrices is of paramount importance. This study was conducted to review high-performance liquid chromatography (HPLC) techniques carried out on MTD and its main metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in the biological samples during 2015-June 2021.

A Sensitive LC-MS/MS Assay for the Quantification of Methadone and its Metabolites in Dried Blood Spots: Comparison With Plasma.

INTRODUCTION: Methadone, a synthetic narcotic, is widely used both in adults and children for pain control and as a replacement drug in opioid use disorder to prevent craving and withdrawal. To support clinical pharmacokinetic trials in neonates, infants, and children, the authors developed and validated a novel, automated, highly sensitive liquid chromatography-electrospray-tandem mass spectrometry ionization (LC-ESI-MS/MS) method for the quantification of methadone and its metabolites, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) and 2-ethyl-5-methyl-3,3-diphenylpyraline (EMDP), in samples collected as dried blood spots. METHODS: Blood was spiked with different concentrations of methadone, EDDP, and EMDP, and blood drops were applied to filter paper cards. Punches of 6.4 mm were removed from the cards, and 600 µL of protein precipitation solution (methanol/0.2M ZnSO4, 7:3, vol/vol) containing the internal standards (methadone-d9 and EDDP-d5) at a concentration of 1 mcg/L was added. The extracts were analyzed using LC-ESI-MS/MS in combination with online extraction. The mass spectrometer was run in the positive multiple reaction monitoring mode, and the total run time was 3.2 minutes. RESULTS: For the dried blood spots, the assay has a lower limit of quantification of 0.1 mcg/L for methadone, EDDP, and EMDP. The range of reliable response for methadone for the ion transition m/z = 310.2→265.1 was 0.1-100 mcg/L and for the ion transition m/z = 310.2→223.1 5-1000 mcg/L. For EDDP, on the range of reliable response for the ion transition, m/z = 278.2→234.3 was 0.1-100 mcg/L and for the ion transition m/z = 278.2→186.1 5-1000 mcg/L. The calibration range for EMDP was 0.1-100 mcg/L. Accuracy (85%-115%) and imprecision (<15%) met predefined acceptance criteria. DISCUSSION: This assay allows for the measurement of small volume blood samples without the need for an intravenous blood draw, and thus, it is suitable for pharmacokinetics studies and therapeutic drug monitoring in pediatric patients.

A comparison of blood toxicology in fatalities involving alcohol and other drugs in patients with an opioid use disorder treated with methadone, buprenorphine, and implant naltrexone.

Background: Methadone, buprenorphine, and implant naltrexone have comparable efficacy in preventing death from drug intoxication during treatment, but there may be differences between treatments in the specific drugs contributing to death and in the risk of death during different phases of treatment.Objective: The objective of this study was to compare concentrations of individual drugs in decedents for evidence that the three medications use to treat opioid use disorders differed in the protection they offered against fatal overdose.Methods: Fatalities with a primary or co-diagnosis of alcohol or other drug poisoning in patients treated with methadone (n = 66, 74.2% male), buprenorphine (n = 54, 74.1% male), or naltrexone (n = 28, 85.7% male) were identified by combining treatment (Monitoring of Drugs of Dependence System and clinical records) and mortality records (Western Australian Death Registry). Quantitative postmortem blood drug analysis data were obtained for drug-related deaths. The presence/absence of drugs were compared between the three medication groups and between phases of treatment (on-treatment/off-treatment).Results: Opioids (89.8%) and benzodiazepines (76.2%) were most commonly identified in postmortem blood. The three medication groups did not differ materially in the drugs present postmortem, except that alcohol was less prevalent in naltrexone-treated cases. Morphine or heroin intoxication was implicated in more patients dying off-treatment than on-treatment but levels of morphine and other drugs were comparable across the two phases.Conclusion: Comparisons of postmortem concentrations of specific drugs indicated that patients treated with methadone, buprenorphine, and implant naltrexone had comparable susceptibilities to lethal co-intoxication and that similar drug mixtures contributed to death.

Layered double hydroxide intercalated with tyrosine for ultrasonic-assisted microextraction of tramadol and methadone from biological samples followed by GC/MS analysis.

A magnetic nanocomposite adsorbent based on Zn-Al layered double hydroxide (LDH) intercalated with tyrosine has been synthesized for ultrasound-assisted extraction of two drugs of abuse: tramadol (TRA) and methadone (MET). Analysis was carried out using gas chromatography-mass spectrometry. The synthesized LDH was characterized by Fourier transform-infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The most important extraction parameters such as type of the elution solvent, pH value of the sample solution, and the amount of the adsorbent were optimized. With assistance of ultrasound radiation, the maximum extraction of target drugs using the fabricated LDH was achieved within 5 min. Under the optimized conditions, the limits of determination were 0.45, 0.45, 2.5, and 0.8 µg L-1 for TRA and 0.15, 0.15, 1.2, and 0.5 µg L-1 for MET in water, urine, plasma, and saliva samples, respectively. The preconcentration factors obtained were in the range of 50-145. The matrix effect for MET and TRA is considerable in plasma (66%, 18%) and saliva (72%, 34%), respectively. The precision was found to be better 11% RSD. The maximum adsorption capacity is 4.84 (mg g-1) (L mg-1)1/n based on the Freundlich isotherm. The proposed method presents good results for trace determination of tramadol and methadone in biological samples with satisfactory repeatability. Graphical abstract.

Enantioselective capillary electrophoresis for pharmacokinetic analysis of methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in equines anesthetized with ketamine and isoflurane.

An enantioselective assay for the determination of methadone and its main metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in equine plasma based on capillary electrophoresis with highly sulfated γ-cyclodextrin as chiral selector and electrokinetic analyte injection is described. The assay is based on liquid/liquid extraction of the analytes at alkaline pH from 0.1 mL plasma followed by electrokinetic sample injection of the analytes from the extract across a buffer plug without chiral selector. Separation occurs cationically at normal polarity in a pH 3 phosphate buffer containing 0.16% (w/v) of highly sulfated γ-cyclodextrin. The developed assay is precise (intra- and interday RSD < 4% and < 7%, respectively), is capable to determine enantiomer levels of methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in plasma down to 2.5 ng/mL, and was successfully applied to monitor enantiomer drug and metabolite levels in plasma of a pony that was anesthetized with racemic ketamine and isoflurane and received a bolus of racemic methadone and a bolus followed by constant rate infusion of racemic methadone. The data suggest that the assay is well suited for pharmacokinetic purposes.

Methadone dosing strategies in preterm neonates can be simplified.

AIMS: A dramatic increase in newborn infants with neonatal abstinence syndrome has been observed and these neonates are frequently treated with complex methadone dosing schemes to control their withdrawal symptoms. Despite its abundant use, hardly any data on the pharmacokinetics (PK) of methadone is available in preterm neonates. Therefore we investigated developmental PK of methadone and evaluated current dosing strategies and possible simplification in this vulnerable population. METHODS: A single-centre open-label prospective study was performed to collect PK data after a single oral dose of methadone in preterm neonates. A population PK model was built to characterize developmental PK of (R)- and (S)-methadone. Model-based simulations were performed to identify a simplified dosing strategy to reach and maintain target methadone exposure. RESULTS: A total of 121 methadone concentrations were collected from 31 preterm neonates. A one-compartment model with first order absorption and elimination kinetics best described PK data for (R)- and (S)-methadone. Clearance increases with advancing gestational age and differs between R- and S-enantiomer, being slightly higher for the former (0.244 vs 0.167 L/h). Preterm neonates reached target exposure after 48 hours with currently used dosing schedules. Output from simulations revealed that target exposures can be achieved with a simplified dosing strategy during the first 4 days of treatment. CONCLUSION: Methadone clearance in preterm neonates increases with advancing gestational age and its disposition is influenced by its chirality. Simulations that account for developmental PK changes indicate a shorter methadone dosing strategy can maintain target exposure to control withdrawal symptoms.

Evaluation of methadone concentrations in bitches and in umbilical cords after epidural or systemic administration for caesarean section: A randomized trial.

OBJECTIVE: To measure plasma methadone concentrations in bitches and the umbilical cords of their puppies after systemic or epidural administration. STUDY DESIGN: Prospective, randomized, clinical study. ANIMALS: A total of 27 healthy pregnant female dogs undergoing caesarean section, 4.3 ± 2.3 years of age and weighing 19.9 ± 13.2 kg. METHODS: The dogs were randomly divided into three groups: 1) intramuscular methadone (0.3 mg kg-1) (group MET; n = 9); 2) epidural methadone (0.1 mg kg-1) (group METEPI; n = 9); and 3) epidural lidocaine (4.4 mg kg-1) [group CON (control group); n = 9]. Ten minutes before induction, methadone was administered intramuscularly to the group MET dogs. Anaesthesia was induced with propofol and maintained with isoflurane. Cardiovascular and respiratory parameters were monitored throughout the anaesthesia. After induction, epidural anaesthesia was administered to dogs in groups METEPI and CON. Before any treatment (T0) and, as soon as the last foetus was removed from the uterus (T1), venous blood samples were collected from each dog into heparinized tubes; the umbilical cords were collected and stored at -80 °C until pharmacological analysis was carried out. The samples were analysed using ultra performance liquid chromatography. RESULTS: The cardiorespiratory parameters of the bitches and of the puppies at birth, and the Apgar scores did not differ significantly between groups. At T1 both the median maternal methadone plasma concentration and the median methadone umbilical cord concentration were higher in group MET compared to group METEPI (p = 0.0018 and p = 0.004, respectively). The maternal plasma concentration was higher than the concentration in the umbilical cords (p = 0.05) in group METEPI but not in group MET (p = 0.25). CONCLUSIONS AND CLINICAL RELEVANCE: Epidural methadone (0.1 mg kg-1) administered to bitches undergoing caesarean section is associated with lower umbilical cord methadone concentrations as compared with intramuscularly administered methadone at higher dosages (0.3 mg kg-1).

The effect of fluconazole on oral methadone in dogs.

OBJECTIVE: To determine the effects of fluconazole on oral methadone pharmacokinetics and central effects mediated by opioid receptors in dogs. STUDY DESIGN: Prospective, incomplete block. ANIMALS: A total of 12 healthy Beagle dogs. METHODS: Dogs were randomly allocated into two groups of six dogs. In total, four treatments (two treatments/group) were administered including: oral methadone (1 mg kg-1); oral fluconazole (5 mg kg-1) every 12 hours starting 24 hours prior to oral methadone (1 mg kg-1); oral fluconazole (2.5 mg kg-1) every 12 hours starting 24 hours prior to oral methadone (1 mg kg-1); and oral fluconazole (5 mg kg-1) every 24 hours starting 12 hours prior to oral methadone (1 mg kg-1). At least 28 days were implemented as a washout period between fluconazole treatments. Rectal temperature (RT), heart rate (HR), respiratory rate (fR), sedation scores and blood samples were obtained for 24 hours after methadone administration. Plasma drug concentrations were measured with liquid chromatography/mass spectrometry. RESULTS: Significantly higher maximum plasma methadone concentration (mean, 25-46 ng mL-1) occurred in all fluconazole-administered treatments than in methadone alone (1.5 ng mL-1). The mean 12 hour methadone plasma concentration in fluconazole treatments was 11-20 ng mL-1. Significantly decreased RT and variable sedation occurred in all fluconazole treatments, but no changes occurred with methadone alone. There were no differences in HR or fR among treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Fluconazole significantly increases the extent and duration of oral methadone exposure in dogs resulting in significant central opioid effects.

A Novel Method for Determination of Methadone in the Serum by High-Performance Liquid Chromatography with Electrochemical Detection.

In March 2013, the clinical use of oral methadone tablets was initiated in Japan. There are many factors responsible for the change in blood concentrations of methadone, and its pharmacokinetics is very complex. Therefore, a simple and accurate measurement method for methadone blood concentrations was developed using HPLC/electrochemical detector (ECD). An eluent of 10 mM Na2HPO4/CH3CN/CH3OH (20 : 19 : 3) was used as the mobile phase. The column was used the XTerra® RP18, and the voltage of the ECD was set at 400 to 800 mV. As a result, the calibration curve was linear in the ranges of 10 to 100 ng/mL (y=5012.7x+1041.1, r=0.999). The intra- and inter-day coefficients of variation were <5.2 and <5.8%, respectively. Therefore, this method was considered to be useful for the measurement of methadone blood levels in cancer patients. Also, using this method, blood methadone concentration was measured over time in a patient with cancer-associated pain who was treated with methadone. The estimated clearance (CL/F) and distribution volume (Vd/F) of methadone were 2.84 L/h and 502.8 L, respectively, and took about two weeks to reach steady state.

Simultaneous chiral separation of tramadol and methadone in tablets, human urine, and plasma by capillary electrophoresis using maltodextrin as the chiral selector.

The stereoselective analysis and separation of racemic drugs play an important role in pharmaceutical industry to eliminate the unwanted isomer and find the right therapeutic control for the patient. Present study suggests a maltodextrin-modified capillary electrophoresis method for a single-run chiral separation of two closely similar opiate pain relief drugs: tramadol (TRA) and methadone (MET). The best separation method possible for the both enantiomers was achieved on an uncoated fused-silica capillary at 25°C using 100 mM phosphate buffer (pH 8.0) containing 20% (w v-1 ) maltodextrin with dextrose equivalent of 4-7 and an applied voltage of 16 kV. Under optimal conditions, the baseline resolution of TRA and MET enantiomers was obtained in less than 12 minutes. The relative standard deviations (n = 3) of 20 µg mL-1 TRA and MET were 2.28% and 3.77%, respectively. The detection limits were found to be 2 µg mL-1 for TRA and 1.5 µg mL-1 for MET. This method was successfully applied to the measurement of drugs concentration in their tablets, urine, and plasma samples.

Methadone Dose Adjustments, Plasma R-Methadone Levels and Therapeutic Outcome of Heroin Users: A Randomized Clinical Trial.

AIMS: We aimed to improve the retention in treatment and therapeutic outcome of methadone maintenance treatment (MMT) patients by adjusting the oral methadone dose in order to reach a "target" plasma R-methadone level (80-250 ng/mL). METHODS: A multicenter randomized controlled trial was organized. RESULTS: The intention-to-treat statistical analysis showed that repeated dose adjustments performed in order to obtain therapeutic plasma R-methadone levels did not improve retention in treatment of heroin-dependent patients. However, patients having plasma methadone levels in the "target range" at the beginning of the study had a better retention in treatment than controls. Furthermore, patients succeeding in keeping plasma R-methadone target levels (per protocol analysis) remained in treatment and improved their social scores better than controls. -Conclusion: Although the primary endpoint of this study was not demonstrated, a post hoc and a per protocol analysis suggested that patients in MMT with plasma R-methadone concentrations in the target range have a better therapeutic outcome than controls.

Postmortem Hyperthermia: Two Case Reports and a Review of the Literature.

In this daily practice, the forensic pathologist is rarely confronted with postmortem hyperthermia associated with the rapid onset of rigor mortis. We report 2 similar cases where the rectal temperature value taken during the on-scene investigations by the forensic pathologist was greater than 40°C (104°F) in both cases, and rigor mortis was complete within less than 6 hours postmortem. The first case was due to a deadly intoxication by ecstasy and the second one to the deadly association of methadone and a possible neuroleptic malignant syndrome. Infection-related deaths were eliminated. Thus, the association of postmortem hyperthermia and rapid-onset rigor mortis would suggest in the first hypothesis a toxic death, particularly 3,4-methylenedioxymethamphetamine. However, an autopsy and toxicological analysis are necessary to confirm the cause of death.

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.

Combined Effect of CYP2B6 Genotype and Other Candidate Genes on a Steady-State Serum Concentration of Methadone in Opioid Maintenance Treatment.

BACKGROUND: A considerable interindividual variability in methadone pharmacokinetics is seen in patients on methadone maintenance treatment. The aim of this study was to clarify the impact of the reduced function CYP2B6*6 variant allele together with variants in other candidate genes on a steady-state methadone concentration in a naturalistic setting. METHODS: Information of methadone serum concentration, dose, age, sex, and CYP2C9, CYP2C19, and CYP2D6 genotypes were collected from a routine therapeutic drug monitoring database, whereas variant alleles in CYP2B6 and CYP3A5 were retrospectively genotyped. Linear mixed model analyses were used to study the impact of gene variants on methadone serum concentration/dose (C/D) ratios, including age, sex, and time since the last dose intake as covariates. RESULTS: Overall, 155 serum samples from 62 patients were included in this study. The estimated mean methadone C/D ratios was 17.8 nmol·L·mg for homozygous carriers of CYP2B6*6, which was significantly (P < 0.001) higher than noncarriers (9.2 nmol·L·mg). There was no difference in C/D ratios between heterozygous carriers of CYP2B6*6 (9.1 nmol·L·mg) and noncarriers. An increase in mean methadone C/D ratios was also seen for homozygous carriers of CYP3A5*3 and heterozygous carriers of CYP2C9*2 or *3 and CYP2C19*2 or *3. CONCLUSIONS: Patients homozygous for CYP2B6*6 had a >90% higher methadone C/D ratio. Genotyping of CYP2B6 may therefore be of value when assessing dose requirements in methadone maintenance treatment.

Dispersion of magnetic graphene oxide nanoparticles coated with a deep eutectic solvent using ultrasound assistance for preconcentration of methadone in biological and water samples followed by GC-FID and GC-MS.

Magnetic graphene nanoparticles coated with a new deep eutectic solvent (Fe3O4@GO-DES) were developed for efficient preconcentration of methadone. The extracted methadone was then analyzed by gas chromatography-flame ionization detection (GC-FID) or gas chromatography-mass spectrometry (GC-MS). Fe3O4@GO-DES were characterized by Fourier transform IR and X-ray diffraction techniques. Ultrasound was used to enhance the dispersion of the sorbent, with a high extraction recovery. Some parameters affecting the extraction recovery, such as pH, type of deep eutectic solvent, sample volume, amount of sorbent, extraction time, and type of eluent, were investigated. Under optimum conditions, the method developed was linear in the concentration range from 3 to 45,000 µg L-1 for GC-FID and from 0.1 to 500 µg L-1 for GC-MS, with a detection limit of 0.8 µg L-1 for GC-FID and 0.03 µg L-1 for GC-MS. The relative standard deviations (n = 6) as the intraday and interday precisions of the methadone spike at a concentration of 100 µg L-1 were 5.8% and 8.4% respectively for GC-FID. The preconcentration factor was 250. Relative recoveries from spiked plasma, urine, and water samples ranged from 95.1% to 101.5%.

Relationship between ABCB1 polymorphisms and serum methadone concentration in patients undergoing methadone maintenance therapy (MMT).

BACKGROUND: Methadone is a substrate of the permeability glycoprotein (P-gp) efflux transporter, which is encoded by the ABCB1 (MDR1) gene. Large interindividual variability in serum methadone levels for therapeutic response has been reported. Genetic variations in ABCB1 gene may be responsible for the variability in observed methadone concentrations. OBJECTIVE: This study investigated the associations of ABCB1 polymorphisms and serum methadone concentration over the 24-hour dosing interval in opioid-dependent patients on methadone maintenance therapy (MMT). METHODS: One hundred and forty-eight male opioid-dependent patients receiving MMT were recruited. Genomic deoxyribonucleic acid (DNA) was extracted from whole blood and genotyped for ABCB1 polymorphisms [i.e. 1236C>T (dbSNP rs1128503), 2677G>T/A (dbSNP rs2032582), and 3435C>T (dbSNP rs1045642)] using the allelic discrimination real-time polymerase chain reaction (PCR). Blood samples were collected at 0, 0.5, 1, 2, 4, 8, 12, and 24 hours after the dose. Serum methadone concentrations were measured using the Methadone ELISA Kit. RESULTS: Our results revealed an association of CGC/TTT diplotype (1236C>T, 2677G>T/A, and 3435C>T) with dose-adjusted serum methadone concentration over the 24-hour dosing interval. Patients with CGC/TTT diplotype had 32.9% higher dose-adjusted serum methadone concentration over the 24-hour dosing interval when compared with those without the diplotype [mean (SD) = 8.12 (0.84) and 6.11 (0.41) ng ml-1 mg-1, respectively; p = 0.033]. CONCLUSION: There was an association between the CGC/TTT diplotype of ABCB1 polymorphisms and serum methadone concentration over the 24-hour dosing interval among patients on MMT. Genotyping of ABCB1 among opioid-dependent patients on MMT may help individualize and optimize methadone substitution treatment.

Risk factors for weight gain during methadone maintenance treatment.

BACKGROUND: Weight gain was reported during methadone maintenance treatment (MMT). However, its relation to eating habits and specific risk factors, including methadone dose or serum level, was limited. The aims of this study were to characterize risk factors for weight gain and to study current eating habits, food preferences, and nutrition knowledge. METHODS: Patients with available measures of weight and height (body mass index [BMI]) at admission to MMT and at follow-up, when methadone serum levels were determined (after 1 year or when stabilized) (N = 114), were studied (using the Addiction Severity Index [ASI], drugs in urine, methadone doses, and serum levels). In addition, 109 current patients with available earlier (5.8 ± 2.6 years earlier) BMI completed eating behavior rating and nutrition knowledge questionnaires, and their current and earlier BMI were compared. RESULTS: The BMI of 114 newly admitted patients increased from 22.5 ± 3.8 to 24.4 ± 4.3 (P < .0005). Once stabilized on methadone, BMI increased further (24.3 ± 4.5 to 25.6 ± 5.0; P < .0005; n = 74), with no change in methadone doses (125.6 ± 32.5 to 128.0 ± 34.1; F = 1.4, P = .2) or serum levels (495.6 ± 263.7 to 539.8 ± 306.2; F = 1.3, P = .2). Repeated-measures analyses revealed that BMI elevation was higher among 45 hepatitis C virus seronegative and 46 non-benzodiazepine-abusing on-admission patients. Those who scored lower on knowledge about healthy diet and showed a higher sweet-foods preference had a higher BMI. CONCLUSION: BMI increased over time, but independent of methadone dosage and blood levels. As expected, worse diet habits and a desire for sweet foods are related to higher BMI. Paradoxically, healthier status (i.e., hepatitis C seronegative, no benzodiazepine abuse) at admission is predictive of greater weight gain during MMT. Education about nutrition habits is recommended.

Effect of steady-state faldaprevir on the pharmacokinetics of steady-state methadone and buprenorphine-naloxone in subjects receiving stable addiction management therapy.

The effects of steady-state faldaprevir on the safety, pharmacokinetics, and pharmacodynamics of steady-state methadone and buprenorphine-naloxone were assessed in 34 healthy male and female subjects receiving stable addiction management therapy. Subjects continued receiving a stable oral dose of either methadone (up to a maximum dose of 180 mg per day) or buprenorphine-naloxone (up to a maximum dose of 24 mg-6 mg per day) and also received oral faldaprevir (240 mg) once daily (QD) for 8 days following a 480-mg loading dose. Serial blood samples were taken for pharmacokinetic analysis. The pharmacodynamics of the opioid maintenance regimens were evaluated by the objective and subjective opioid withdrawal scales. Coadministration of faldaprevir with methadone or buprenorphine-naloxone resulted in geometric mean ratios for the steady-state area under the concentration-time curve from 0 to 24 h (AUC(0-24,ss)), the steady-state maximum concentration of the drug in plasma (C(max,ss)), and the steady-state concentration of the drug in plasma at 24 h (C(24,ss)) of 0.92 to 1.18 for (R)-methadone, (S)-methadone, buprenorphine, norbuprenorphine, and naloxone, with 90% confidence intervals including, or very close to including, 1.00 (no effect), suggesting a limited overall effect of faldaprevir. Although individual data showed moderate variability in the exposures between subjects and treatments, there was no evidence of symptoms of opiate overdose or withdrawal either during the coadministration of faldaprevir with methadone or buprenorphine-naloxone or after faldaprevir dosing was stopped. Similar faldaprevir exposures were observed in the methadone- and buprenorphine-naloxone-treated subjects. In conclusion, faldaprevir at 240 mg QD can be coadministered with methadone or buprenorphine-naloxone without dose adjustment, although given the relatively narrow therapeutic windows of these agents, monitoring for opiate overdose and withdrawal may still be appropriate. (This study has been registered at ClinicalTrials.gov under registration no. NCT01637922.).