Within- and between- subject variability in methadone pharmacokinetics and pharmacodynamics in methadone maintenance subjects

Night-to-night variability of objective sleep outcomes in youth Middle Eastern football players

OBJECTIVE

To describe components of night-to-night variation in objective measures of sleep.

METHODS

We conducted a secondary data analysis of consecutive and chronologically ordered actigraphy-based measurements for time in bed (min), time asleep (min), and wake-after-sleep onset (min). This investigation examined 575 individual night-based measures available for a sub-sample of fifty-two, male youth Middle Eastern football players tracked over a 14-day surveillance period (chronological age range: 12.1 to 16 years). Distinct multivariable-adjusted generalized additive models included each objective sleep outcome measure as dependent variable and disaggregated components of variation for night measurement-by-sleep period interaction, week part (weekday or weekend), and study participant random effects from within-subject night-to-night sleep variation.

RESULTS

The within-subject standard deviation (SD) of ±98 min (95% confidence interval [CI], 92 to 104 min) for time in bed, ±87 min (95%CI, 82 to 93 min) for time asleep, and ±23 min (95%CI, 22 to 25 min) for wake-after-sleep-onset overwhelmed other sources of variability and accounted for ∼44% to 53% of the overall night-to-night variation. The night measurement-by-fragmented sleep period interaction SD was ±83 min (95%CI, 44 to 156 min) for time in bed, ±67 min (95%CI, 34 to 131 min) for time asleep, and ±15 min (95%CI, 7 to 32 min) for wake-after-sleep-onset that accounted for ∼22% to 32% of each sleep outcome measure overall variability.

CONCLUSIONS

Substantial random night-to-night within-subject variability poses additional challenges for strategies aiming to mitigate problems of insufficient and inconsistent sleep that are detrimental to school learning and youth athlete development processes.

Effect of rilpivirine on the pharmacokinetics of methadone in HIV-Infected Chinese patients

Background: The combination of rilpivirine with methadone may result in complex interactions secondary to the induction of oxidative metabolism by rilpivirine. Research design and methods: TMC278IFD4007 was a single-center, prospective, open-label, multiple-dose study with 12 HIV-infected Chinese participants. The objective was to evaluate the potential effect of rilpivirine on the pharmacokinetics of methadone. The participants received a daily dose of 25 mg rilpivirine for 11 days with individualized methadone ranging from 25 to 100 mg. Pharmacokinetic studies of methadone were conducted on day 1 and 11. Opiate withdrawal symptoms were evaluated. Results: A large inter-subject variability was noted in methadone pharmacokinetics. Rilpivirine increased methadone minimum and maximum plasma concentrations (Cmin; Cmax) and area under the plasma concentration-time curve versus methadone alone (least-square mean ratio; 90% confidence interval) by 5% (1.05; 0.46, 2.39), 5% (1.05; 0.73, 1.52), and 6% (0.75; 0.74, 1.50) as measured in S-methadone, and 5% (1.05; 0.50, 2.22), 5% (1.05; 0.74, 1.50), and 5% (1.05; 0.76, 1.46) as measured in R-methadone, respectively. No opioid withdrawal symptoms or methadone dose adjustments were reported. Co-administration was well tolerated without serious adverse effects or discontinuations. Conclusion: Concomitant administration of rilpivirine was unlikely to have significant effects on the pharmacokinetics of methadone.

Characterizing within-subject variability in quantified measures of balance control: A cohort study

BACKGROUND

To longitudinally assess individuals using quantified measures, we must characterize within-subject variability (WSV) of the measures.

RESEARCH QUESTION

What is the natural within-subject variability (WSV) that can be expected in postural control over 3+ days?

METHODS

Thirteen individuals without orthopedic or neurologic impairment (mean(SD) = 55 (9) years; 76 (18) kg; 11 females/2 males) were recruited from a community workplace and consented to participate. Participants stood quietly with eyes closed (QEC) on a force platform (5 x 1 min x 6 days) in two stances: comfortable and narrow. We recorded center of pressure (COP) and calculated COP-based balance parameters. To analyze variance components, we applied a linear mixed model for repeated measures, calculating within-subject standard deviation (SDws) from the pooled variance not attributable to between-subject variability. To estimate WSV, we scaled SDws by a confidence interval (CI) factor (e.g. WSV at the 95%CI = WSV₉₅ = SDws * 1.96) and report WSV₉₅ for a range of conditions previously reported in the literature and the following measures previously found sensitive to or predictive of health: (primary) WSV₉₅ of root-mean square amplitude of medial-lateral COP during QEC (RMSml); (secondary) WSV₉₅ of COP ellipse area (COPa); (secondary) WSV₉₅ of mean medial-lateral COP velocity (COPvml) during QEC.

RESULTS

WSV₉₅ was estimated at RMSml = 0.8 mm, COPa = 99mm², and COPvml = 1.1 mm/s among healthy, middle-aged participants standing comfortably for one recommended data duration (4 × 30 s trials). A look up table provides values for alternate protocols that have been suggested in the literature and might prove relevant for clinical translation.

SIGNIFICANCE

This work advances longitudinal assessment of individuals using quantified measures of postural control. Results enable practitioners/researchers to assess an individual's progress, maintenance, or decline relative to WSV at a defined CI level.

Pharmacoepigenomics of opiates and methadone maintenance treatment: current data and perspectives

Current treatments of opioid addiction include primarily maintenance medications such as methadone. Chronic exposure to opiate and/or long-lasting maintenance treatment induce modulations of gene expression in brain and peripheral tissues. There is increasing evidence that epigenetic modifications underlie these modulations. This review summarizes published results on opioid-induced epigenetic changes in animal models and in patients. The epigenetic modifications observed with other drugs of abuse often used by opiate abusers are also outlined. Specific methadone maintenance treatment induced epigenetic modifications at different treatment stages may be combined with the ones resulting from patients’ substance use history. Therefore, research comparing groups of addicts with similar history and substances use disorders but contrasting for well-characterized treatment phenotypes should be encouraged.

Variability of response to methadone: genome-wide DNA methylation analysis in two independent cohorts

Aim: Methadone maintenance treatment is characterized by large interindividual dose variability. The aim of this study was to evaluate whether DNA methylations are associated with daily dose of methadone. Materials & methods: Subjects stabilized at high (n = 12) or low (n = 12) methadone doses were selected from two independent cohorts (French and Swiss). DNA methylation patterns were analyzed using HumanMethylation450 BeadChips. Results: In total, 584 differentially methylated sites were identified in the French cohort corresponding to 352 genes. Of these, 26 were replicated in the Swiss cohort. The methylation status of 13 genes varied similarly in both cohorts and calcium signaling pathway was significantly enriched. Conclusion: Our results indicate that differentially methylated sites are associated with methadone daily dose and give insights into the molecular pathways underlying this interindividual dose variability.

Determination and Validation of a Solid-phase Extraction Gas Chromatography-mass Spectrometry for the Quantification of Methadone and Its Principal Metabolite in Human Plasma

This study aimed to develop a solid-phase extraction gas chromatography-selected ion monitoring-mass spectrometry method for the determination of methadone (MDN) and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in human plasma. The linear response was obtained over the concentration range from 10 to 2000 ng/mL for MDN and EDDP. The absolute recoveries of MDN and EDDP were 95.9%–98.9% and 94.8%–102.4%, with relative standard deviation (RSD) ranging from 1.8% to 2.7% and 1.8% to 3.9%, respectively. The intra- and interday precisions were found to be less than 5% for both analytes. The limits of detection of MDN and EDDP were 4 and 5 ng/mL, respectively. The presented method was convenient for therapeutic drug monitoring and pharmacokinetic studies in patients on heroin-assisted MDN therapy.

Gender differences in pharmacokinetics and pharmacodynamics of methadone substitution therapy

Gender-related differences in the pharmacological effects of drug are an emerging topic. This review examines gender differences in both pharmacokinetic and pharmacodynamic aspects of methadone, a long-acting opioid agonist that is prescribed as a treatment for opioid dependence and the management of chronic pain.

Method: We performed a search in the Medline database from 1990 to 2014 in order to find published literature related to gender differences in pharmacokinetics (PK) and pharmacodynamics (PD) of methadone.

Results: None of the studies were carried out with the primary or secondary aim to identify any gender differences in the pharmacokinetic profile of methadone. Importantly; high inter-subjects variability in PK parameters was found also intra female population. The reported differences in volume of distribution could be ascribed to the physiological differences between men and women in body weight and composition, taking into account that the dose of methadone was established irrespective of body weight of patients (Peles and Adelson, 2006). On the other hand, the few studies present in literature found no gender difference in some direct pharmacodynamic parameters. Some reports have suggested that female gender is associated with an increased risk for long-QT-related cardiac arrhythmias in methadone maintenance subjects.

Conclusion: Even though it may be too simplistic to expect variability only in one parameter to explain inter-individual variation in methadone response, we believe that a better knowledge of gender-related differences might have significant implications for better outcomes in opioid dependence substitution therapy in women.

A rapid UPLC-MS/MS method for simultaneous determination of flunitrazepam, 7-aminoflunitrazepam, methadone and EDDP in human, rat and rabbit plasma

A simple, high-throughput, sensitive LC-ESI-MS/MS method is presented for the simultaneous determination of methadone (MET), flunitrazepam (FNZ) and their major metabolites, EDDP (2-ethilidene-1,5-dimethyl-3,3-diphenylpyrrolidone) and 7-aminoflunitrazepam (7-AFNZ), respectively, in human, rat and rabbit plasma. The isolation of the selected compounds involved a liquid-liquid extraction with ethyl acetate at a basic pH. Good chromatographic separation was achieved on a HSS T3 column (1.8 μm particle size), with a 3 min gradient elution using a mixture of acetonitrile with 0.1% formic acid (solvent A) and 5mM ammonium acetate (solvent B) as the mobile phase. The tandem mass spectrometric detection was performed in multiple reaction monitoring (MRM) mode with ionization of the analytes in positive mode. The assay was fully validated according to current acceptance criteria for bioanalytical methods validation. It was proved to be linear in the range of 0.5-250 ng/mL, with adequate accuracy and precision over this range. Based on accuracy and CV% values the LOQ and ULOQ values were set at 0.509 ng/mL and 2036 ng/mL for MET, 0.520 ng/mL and 2080 ng/mL for EDDP, 0.524 ng/mL and 2096 ng/mL for FNZ and 0.528 ng/mL and 2114 ng/mL for 7-AFNZ, respectively. The method was tested for potential matrix effects, without observing significant ion suppression. The investigated compounds stability was examined in plasma at room temperature and after three freeze-thaw cycles and in the final extract when maintained at 4 °C in the autosampler. Potential stability issues were observed only for FNZ at room temperature. The method was successfully applied to quantify the selected compounds in human, rat and rabbit plasma samples, after exposure to FNZ or simultaneous exposure to FNZ and MET.

Estimation of lean body weight in older community-dwelling men

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT? * Lean mass decreases with age while total body fat increases, leading to changes in the pharmacokinetics and pharmacodynamics of drugs. * Dual-energy X-ray absorptiometry (DXA) is a useful reference method to measure lean body weight but may not be readily utilized clinically. * Limited methods for measurement of lean body weight using easily obtainable participant characteristics, such as height and weight, have been validated for use in people aged > or =65 years. WHAT THIS STUDY ADDS * This study has shown that lean body weight can be estimated using three different equations from easily obtainable participant characteristics with results comparable to DXA-derived estimates. * These equations may be useful tools to estimate lean body weight in situations where DXA is not practical. AIMS Lean body weight (LBW) decreases with age while total body fat increases, altering drug pharmacokinetics. The aim of this study was to evaluate the ability of the LBW equation to predict dual-energy X-ray absorptiometry (DXA)-derived fat free mass (FFM(DXA)) in older community-dwelling males compared with that of two existing FFM equations: the Heitmann and Deurenberg equations. METHODS Data were obtained from 1655 older men enrolled in the Concord Health and Ageing in Men Project. The predictive performance of the LBW and FFM equations to predict FFM(DXA) accurately was assessed graphically using Bland-Altman plots and quantitatively for precision and bias using the method of Sheiner and Beal in all participants and in frailty and body mass index (BMI) subgroups. RESULTS The LBW and Heitmann equations consistently overestimated FFM(DXA) for all frailty and BMI subgroups with a mean difference [95% confidence interval (CI)] of 5.5 kg (-0.65, 11.63 kg) and 3.34 kg (-2.84, 9.64 kg), respectively. The Deurenberg equation overestimated FFM(DXA) for overweight participants but underestimated FFM(DXA) for not-frail participants, with a mean difference (95% CI) of 1 kg (-7.23, 5.25 kg) for all participants. CONCLUSION LBW and FFM estimated using these equations give results comparable to DXA-derived FFM. The LBW and Heitmann equations provide a more consistent estimate of FFM(DXA) in all frailty and BMI groups despite the Deurenberg equation having the smallest mean difference. Further studies to determine whether the LBW equation is a clinically useful substitute for weight when determining drug dose in older people appear warranted.

Population pharmacokinetics of buprenorphine following a two-stage intravenous infusion in healthy volunteers

OBJECTIVE

The aim of this investigation was to characterize the pharmacokinetics of buprenorphine following administration of an intravenous (i.v.) infusion. To date, the population kinetics of buprenorphine has been described for bolus administration only.

METHODS

Twenty-three healthy male volunteers aged 21-40 years received 0.6 mg buprenorphine by means of an i.v. infusion over a 150-min period. The plasma concentration-time profiles up to 24 h post-administration of the infusion were subjected to population pharmacokinetic modelling using NONMEM: software.

RESULTS

A three-compartment model best described the plasma concentration-time course. Body weight was found to be a significant covariate for elimination clearance in a linear fashion. Inter-individual variability (coefficient of variation) was estimable for apparent clearance (CL, 23.5%), central distribution volume (V(1), 81.8%), peripheral distribution volume 1 (V(2), 23.7%) and inter-compartmental clearances between V(1) and V(2) (Q(2), 34.8%). Models using parameters derived from previous published data obtained after an i.v. bolus of buprenorphine were found to overestimate the measured buprenorphine concentrations during the course of the i.v. infusion and to underpredict those following the end of the infusion.

CONCLUSION

Most parameters describing the disposition of buprenorphine in the volunteers showed only moderate inter-subject variability. However, the parameters differed from those previously reported for i.v. bolus administration. We conclude that pharmacokinetic parameter estimates obtained from the appropriate study in accordance to the mode of administration should be used in the design of dose regimens of buprenorphine.

Case report: quantification of methadone-induced respiratory depression using toxicokinetic/toxicodynamic relationships

Introduction

Methadone, the most widely delivered maintenance therapy for heroin addicts, may be responsible for life-threatening poisonings with respiratory depression. The toxicokinetics and the toxicokinetic/toxicodynamic (TK/TD) relationships of methadone enantiomers have been poorly investigated in acute poisonings. The aim of this study was to describe the relationships between methadone-related respiratory effects and their corresponding concentrations.

Methods

We report a 44-year-old methadone-maintained patient who ingested a 240-mg dose of methadone. He was found comatose with pinpoint pupils and respiratory depression. He was successfully treated with intravenous naloxone infusion over the course of 31 hours at a rate adapted to maintain normal consciousness and respiratory rate. We performed a TK/TD analysis of the naloxone infusion rate needed to maintain his respiratory rate at more than 12 breaths per minute (as toxicodynamics parameter) versus plasma R,S- and R-methadone concentrations (as toxicokinetics parameter), determined using an enantioselective high-performance liquid chromatography assay.

Results

Initial plasma R,S-methadone concentration was 1,204 ng/ml. Decrease in plasma R- and S-methadone concentrations was linear and demonstrated a first-order pharmacokinetics (maximal observed concentrations 566 and 637 ng/ml, half-lives 16.1 and 13.2 hours, respectively). TK/TD correlation between naloxone infusion rate and R,S- and R-methadone concentrations fitted well a sigmoidal E_max model (concentration associated with a half-maximum effect [EC₅₀] 334 and 173 ng/ml, Hill coefficient 10.0 and 7.8, respectively). In our chronically treated patient, EC₅₀ values were in the range of previously reported values regarding methadone analgesic effects, suggesting that plasma methadone concentrations to prevent withdrawal are lower than those associated with methadone analgesic effects.

Conclusion

After the ingestion of a toxic dose of a racemic mixture, plasma R- and S-enantiomer concentrations decreased in parallel. Despite large inter-individual variability in methadone toxicokinetics and toxicodynamics, TK/TD relationships would be helpful for providing quantitative data regarding the respiratory response to methadone in poisonings. However, further confirmatory TK/TD data are needed.

Integrating in vitro ADMET data through generic physiologically based pharmacokinetic models

Early estimation of kinetics in man currently relies on extrapolation from experimental data generated in animals. Recent results from the application of a generic physiologically based model, Cloe PK) (Cyprotex), which is parameterised for human and rat physiology, to the estimation of plasma pharmacokinetics, are summarised in this paper. A comparison with predictive methods that involve scaling from in vivo animal data can also be made from recently published data. On average, the divergence of the predicted plasma concentrations from the observed data was 0.47 log units. For the external test set, > 70% of the predicted values of the AUC were within threefold of the observed values. Furthermore, the model was found to match or exceed the performance of three published interspecies scaling methods for estimating clearance, all of which showed a distinct bias towards overprediction. It is concluded that Cloe PK, as a means of integrating readily determined in vitro and/or in silico data, is a powerful, cost-effective tool for estimating exposure and kinetics in drug discovery and risk assessment that should, if widely adopted, lead to major reductions in the need for animal experimentation.

Fluctuations in (R,S)-methadone pharmacokinetics and response among long-term methadone maintenance patients

Knowledge of how methadone disposition may fluctuate during the course of maintenance treatment is presently limited. This study investigated long-term fluctuations in methadone pharmacokinetics in five methadone maintenance patients who participated in two 24-hour testing sessions separated by at least one year. Results indicated substantial fluctuations between sessions in dose-corrected average steady-state plasma (R)-methadone concentrations (Cav), ranging from a 51% decrease to a 466% increase. These fluctuations were not consistently associated with changes in methadone dose or self-reported withdrawal status. The plasma (S)-:(R)-methadone Cav ratio increased significantly (12%, P = 0.04) between the sessions, suggesting a different pattern of long-term change in the pharmacokinetics of each enantiomer over time. The pronounced and variable fluctuations in methadone disposition evident in these patients highlight the need for an individualized approach to patient dosing and monitoring.