Enantioselective high-performance liquid chromatography determination of methadone enantiomers and its major metabolite in human biological fluids using a new derivatized cyclodextrin-bonded phase

Enantiomeric methadone quantitation on real post-mortem dried matrix spots samples: Comparison of liquid chromatography and supercritical fluid chromatography coupled to mass spectrometry

This study describes two bioanalytical methods for the quantitation of the two methadone enantiomers in dried matrix spots using high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) and high performance supercritical chromatography tandem mass spectrometry (HPSFC-MS/MS). Dried matrix spots were obtained by spotting 10 µL of each sample fluid on a Whatman paper. Methadone and its main metabolite, EDDP, were extracted with 100 µL methanol and subsequently injected into the LC-MS/MS and SFC-MS/MS systems. Enantiomeric separation was achieved with AGP-column for the LC conditions and with Chiralpak IH-3 in SFC. The two methods were fully validated and 93 post-mortem samples were analysed with both analytical methods. Results from validation parameters and results obtained for all post-mortem samples were compared with a significant spearman correlation of r_s = 0.9978 for R-methadone and r_s = 0.9981 for S-methadone. The LC method provided better results in terms of uncertainty, retention factor and resolution, whereas SFC provides better sensitivity, with lower LOD. Median R-/S-methadone ratio in peripheral blood was found equal to 1.60 (N = 32), varying from 0.79 to 4.23. The reported values were in good agreement with previously published results. Based on the results obtained here, SFC-MS/MS can be considered a reliable alternative to the widely used LC-MS/MS for the quantitation of methadone enantiomers in bioanalysis and should be evaluated for other bioanalytical methods. Both methods can be easily and quickly used in toxicological routine analysis for the methadone quantitation in human fluids matrices, even if considering that the polysaccharide coated column IH-3 used in SFC does not allow the enantiomeric EDDP separation.

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.

Precise simultaneous quantification of methadone and cocaine in rat serum and brain tissue samples following their successive i.p. administration

A sensitive high-performance liquid chromatography (HPLC) assay with dual UV detection has been developed and validated for the simultaneous quantification of methadone and cocaine in rat serum and brain tissue samples. Liquid-liquid extraction using hexanes was applied for samples extraction with Levo-Tetrahydropalmatine (L-THP) as the internal standard. Chromatographic separation of the analytes was achieved on a reversed-phase Waters Symmetry^® C₁₈ column (150mm×4.6mm, 5μm). A gradient elution was employed with a mobile phase consisting of 5mM potassium phosphate containing 0.1% triethylamine (pH=6.5) (A) and acetonitrile (B) with a flow rate of 1mL/min. UV detection was employed at 215nm and 235nm for the determination of methadone and cocaine, respectively. The calibration curves were linear over the range of 0.05-10μg/mL for both methadone and cocaine. The assay was validated according to FDA guidelines for bioanalytical method validation and results were satisfactory and met FDA criteria. Inter-day accuracy values of serum and brain samples ranged from 96.97 to 105.59% while intra-day accuracy values ranged from 91.49 to 111.92%. Stability assays showed that both methadone and cocaine were stable during sample storage, preparation, and analytical procedures. The method was successfully used to analyze biological samples obtained from a drug- drug interaction pharmacokinetics (PK) study conducted in rats to investigate the effect of methadone on cocaine PK. Our method not only can be used for bioanalysis of samples obtained from rats but also can potentially be applied to human biological serum samples to monitor compliance to methadone maintenance therapy (MMT) and to detect possible cocaine-methadone co-abuse.

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.

[Evaluation of the Methadone Maintenance Program of the Risaralda Mental Hospital]

BACKGROUND

Psychosocial care and methadone maintenance treatment (MMT) are the preferred strategies for the management of heroin addicts, but the results are still unsatisfactory, justifying the search and intervention of the factors influencing the response to treatment.

METHODOLOGY

In order to determine the contribution of demographic, clinical and genetic variables on serum concentrations and response to methadone, we investigated patients on MMT, who were receiving methadone in supervised and unchanged doses at least during the previous two weeks. The age, gender, body mass index (BMI), duration of heroin abuse, addiction to other drugs, criminal background, current daily methadone doses, time spent in the TMM, comorbidity and concomitant medication were recorded. Blood samples were taken for the determination of serum levels of racemic methadone and its R and S-enantiomers, and for typing of candidate alleles of POR, CYP2B6, ABCB1, GRIN1, OPRM1, SLC6A3, DßH and ARRB2 genes, all associated with the metabolism, tissue distribution and mechanism of action of methadone. Methadone quantification was by HPLC-DAD, and the detection of genetic markers by Real Time PCR and VNTR methods.

RESULTS

A total of 80 subject volunteers were enrolled, with a mean age of 23.5 (5) years (86% male), all of them were addicts of multiple drugs, 60% with a criminal background, 5.1 (2.9) years taking heroin, and 5.3 (4) months on MMT, and taking a supervised dose of 41 (12) mg/day methadone. The (R), (S) and (R, S) methadone enantiomer trough plasma levels were, 84 (40), 84 (42), and 168 (77) ng/mL, respectively. All genotypes were in Hardy-Weinberg equilibrium. The two urine tests were negative for heroin in 61.3% (49/80) of the volunteers, the decline in cocaine/crack use was 83%, 30% of marijuana, and other psychoactives (inhalants, benzodiazepines, amphetamines) decreased to zero, while the consumption of snuff remained at 93.5% (75/80). Blood concentrations of racemic methadone and its enantiomers were significantly associated with the dose/day of the medication, but none of the other demographic, clinical or genetic variables impacted on serum levels of methadone. As for the results of the MMT, non-users and occasional users of heroin, as well as those who stopped taking other psychoactive drugs, and the ones who did not, were similar as regards the demographic, genetic and clinical variables. This included the blood metahdone concentrations, except for individuals who did not reduce their consumption of other psychoactives other than heroin, who had significantly (P=.03) higher blood levels of S-methadone, compared with those who did stop taking them.

CONCLUSIONS

There was a significant reduction in the consumption of heroin and other psychoactives, and social rehabilitation of patients. However, the extensive overlap between effective and ineffective doses of methadone suggests the presence of personal and social variables that transcend the simple pharmacological management. These probably need to be addressed more successfully from the psychosocial features, particularly as regards to identifying and overcoming relapse-trigger experiences, as well as certain features of the patient, such as their psychological distress level or their psychiatric disorders.

Evaluation of metabolite/drug ratios in blood and urine as a tool for confirmation of a reduced tolerance in methadone-related deaths in Denmark

BACKGROUND

Methadone blood concentrations in fatal cases are highly variable and there is an appreciable overlap between therapeutic methadone concentrations and the concentrations detected in fatalities. As with other opioids, the background of these methadone-related deaths is unclear. The aim of this study was to investigate if short-time abstinence was contributing to the cause of death in methadone-related deaths by evaluation of the EDDP/methadone ratio in blood and urine.

METHODS

Samples of blood and urine were collected from 103 autopsy cases and analysed for the concentrations of methadone and its main metabolite EDDP. The cases were divided into three groups according to the cause of death: cases where methadone was the cause of death (N=67), cases where poly-drug poisoning including methadone was the cause of death (N=24) and cases where death were caused by other factors (N=12). Urine samples from 11 living persons receiving methadone were also included.

RESULTS

In general, a substantial overlap of the methadone concentrations in blood and urine was seen between the groups. There was a tendency of lower median EDDP/methadone urinary ratios in the methadone poisoning group (median: 1.0), poly-drug poisoning group (median: 0.94) and in the fatalities not related to methadone (median: 1.1) compared to the living subjects in methadone treatment (median: 1.6), although the differences were not significant.

CONCLUSION

It was not possible to reveal a possible abstinence period prior to death by using the EDDP/methadone ratio in blood and urine in methadone-related deaths.

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.

Validation and long-term evaluation of a modified on-line chiral analytical method for therapeutic drug monitoring of (R,S)-methadone in clinical samples

Matrix effects, which represent an important issue in liquid chromatography coupled to mass spectrometry or tandem mass spectrometry detection, should be closely assessed during method development. In the case of quantitative analysis, the use of stable isotope-labelled internal standard with physico-chemical properties and ionization behaviour similar to the analyte is recommended. In this paper, an example of the choice of a co-eluting deuterated internal standard to compensate for short-term and long-term matrix effect in the case of chiral (R,S)-methadone plasma quantification is reported. The method was fully validated over a concentration range of 5-800 ng/mL for each methadone enantiomer with satisfactory relative bias (-1.0 to 1.0%), repeatability (0.9-4.9%) and intermediate precision (1.4-12.0%). From the results obtained during validation, a control chart process during 52 series of routine analysis was established using both intermediate precision standard deviation and FDA acceptance criteria. The results of routine quality control samples were generally included in the +/-15% variability around the target value and mainly in the two standard deviation interval illustrating the long-term stability of the method. The intermediate precision variability estimated in method validation was found to be coherent with the routine use of the method. During this period, 257 trough concentration and 54 peak concentration plasma samples of patients undergoing (R,S)-methadone treatment were successfully analysed for routine therapeutic drug monitoring.

Fast gas chromatography/mass spectrometric assay for the validated quantitative determination of methadone and the primary metabolite EDDP in whole blood

A toxicological analysis was developed and validated for simultaneous screening and quantification of methadone (METH) and its primary metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP). The method employs microscale liquid-liquid extraction (microLLE) and direct injection of a separated aliquot of the organic layer into a gas chromatography/mass spectrometric (GC/MS) system without any other pre-treatment stages. A fast GC/MS runtime (total 5.8 min; METH, Rt = 3.55 min; EDDP, Rt = 3.40 min) combined with rapid sample preparation allowed cost-efficient and routinely applicable performance with a low amount of manual work. The validated parameters included: linearity (25-1000 ng mL(-1) both; R(METH)2 = 0.998 and R(EDDP)2 = 0.997), accuracy (Bias(METH): from -0.05 to 11.3%, Bias(EDDP): from 1.11 to 4.37%); intra and inter-assay precision (RSD(METH): from 2.4 to 3.9%, from 4.89 to 10.3%; RSD(EDDP): from 4.50 to 6.20%, from 4.57 to 15.2%), extraction efficiency (METH = 95.5%; EDDP = 90.6%), LOQ(Meth,EDDP) = 25 ng mL(-1). Samples were stable for at least 25 h and no selectivity problems or baseline interference were observed. The method should be applicable for identifying and quantitative confirmation of possible misuse and/or illegal use of METH in toxicological cases.

Can Saliva Replace Plasma for the Monitoring of Methadone?

The aims of this study were to determine the relationship between saliva and plasma methadone concentrations and the influence of variability in saliva pH. Saliva and plasma samples were taken before the daily dose of methadone in 60 patients undergoing methadone maintenance treatment (MMT). Saliva pH was measured immediately after sampling, and concentrations of (RS)-, (R)-, and (S)-methadone in saliva and plasma were assayed by LC/MS. In addition, unbound (R)- and (S)-methadone concentrations were measured in plasma samples by ultrafiltration. Plasma binding and pH differences between plasma and saliva were then used to estimate methadone saliva/plasma ratios and to compare them with observed values. Saliva pH ranged from 5.1 to 7.6 (mean +/- SD, 6.7 +/- 0.5). Plasma and saliva concentrations correlated weakly [(RS)-, r = 0.14, P = 0.007, n = 44; (R)-, r = 0.10, P = 0.04, n = 43; (S)-, r = 0.22, P = 0.002, n = 43], and the mean saliva-to-plasma methadone concentration ratios were 1.1 (+/-1.3 SD), 1.5 (+/-1.5), and 0.8 (+/-0.8), for (RS)-, (R)-, and (S)-methadone, respectively. Corresponding values based on unbound concentrations of methadone in plasma were 21 (+/-20.6, n = 31), 21 (+/-19, n = 34), and 17 (+/-15, n = 36). The salivary concentration-to-dose ratios showed statistically significant but weak inverse correlations with saliva pH [(RS)-, r = 0.27, P < 0.001; (R)-, r = 0.25, P < 0.001; (S)-, r = 0.29, P < 0.001, respectively]. There were significant correlations between predicted and observed saliva/plasma ratios [(RS)-, r = 0.44, P < 0.001, n = 31; (R)-, r = 0.58, P < 0.001, n = 32; (S)-, r = 0.10, P = 0.04, n = 34], but the mean predicted saliva concentrations were about 5 times lower than the mean observed values. The poor correlations between salivary and plasma methadone concentrations observed in this study are partly related to the effect of variable saliva pH. However, saliva pH explained only 10%-36% of the total variation. As a conclusion, monitoring methadone concentrations in saliva may not be a useful alternative to plasma concentration measurements. Correction for saliva pH measured immediately after collection improves the relationship between saliva and plasma methadone concentration, but most of the variation remains unexplained.

Determination of total and free concentrations of the enantiomers of methadone and its metabolite (2-ethylidene-1,5-dimethyl-3,3-diphenyl-pyrrolidine) in human plasma by enantioselective liquid chromatography with mass spectrometric detection

A sensitive enantioselective liquid chromatographic assay with mass spectrometric detection (LC-MS) has been validated for the determination of total and free plasma concentrations of (R)- and (S)-methadone (Met) and (R)- and (S)-2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP, the primary metabolite of Met), using their respective deuterium-labeled compounds as internal standards [(R,S)-d3-Met and (R,S)-d3-EDDP]. For total drug determinations, 1 ml human plasma was extracted, using a cation-exchange solid-phase extraction cartridge; the eluate was evaporated, reconstituted in the mobile phase, and injected into the LC-MS system. The free fractions of Met and EDDP were determined, using 500 microl of plasma, which were placed in an ultrafiltration device and centrifuged at 2000 x g until 250 microl of filtrate was collected. The filtrate was extracted as described above and analyzed. Enantioselective separations were achieved using an alpha1-acid glycoprotein chiral stationary phase, a mobile phase composed of acetonitrile-ammonium acetate buffer [10 mM, pH 7.0] (18:82, v/v), a flow rate of 0.9 ml/min at 25 degrees C. Under these conditions, enantioselective separations were observed for Met (alpha = 1.30) and EDDP (alpha = 1.17) within 15 min. Met, EDDP, [2H3]-Met and [2H3]-EDDP were detected using selected ion monitoring at m/z 310.30, 278.20, 313.30, and 281.20, respectively. Linear relationships between peak height ratio and drug-enantiomer concentrations were obtained for Met in the range 1.0-300.0 ng/ml, and for EDDP from 0.1 to 25.0 ng/ml with correlation coefficients greater than 0.999, where the lower limit of quantification (LLOQ) was 1 ng/ml for Met and 0.1 ng/ml for EDDP. The relative standard deviation (R.S.D.) expressed as R.S.D. for the intra- and inter-day precision of the method were < 5.3% and the R.S.D. for accuracy was < 5.0%. The method was used to analyze plasma samples obtained from patients enrolled in a Met-maintenance program.

Definite peak identification of (R)-and (S)-methadone and (R)- and (S)-EDDP using established HPLC and CE methods

Methadone is widely used for the treatment of opioid dependence. HPLC and CE are widespread methods for drug monitoring and metabolism studies. Although the methods are widely used for methadone and its main metabolite EDDP [1, 2], a definite direct peak identification for EDDP enantiomers is not described. This study describes a method for specific identification of each peak in the chromatogram and electropherogram of methadone analysis. The result of the study demonstrates differences in the elution order of the enantiomers of methadone and EDDP due to the technique used for analysis. The elution order of EDDP using HPLC is interchanged with respect to the order of the peaks in the electropherogram.

Quantitative determination of the enantiomers of methadone and its metabolite (EDDP) in human saliva by enantioselective liquid chromatography with mass spectrometric detection

A sensitive enantioselective liquid chromatographic assay with mass spectrometric detection (LC-MS) has been developed and validated for the simultaneous determination of saliva concentrations of (R)- and (S)-methadone (Met) and (R)- and (S)-2-ethylidene-1,5-dimethyl-3,3-diphenyl-pyrrolidine (EDDP, a primary metabolite of Met). Saliva specimens were collected using Salivette devices (Sarsedt), and centrifuged; collected saliva was then spiked with deuterated internal standards, D3-Met and D3-EDDP, and directly injected into the LC-MS. Enantioselective separations were achieved on a liquid chromatographic chiral stationary phase (CSP) based upon immobilized alpha(1)-acid glycoprotein (AGP) using a mobile phase composed of acetonitrile: ammonium acetate buffer (10mM, pH 7.0) in a ratio of 18:82 (v/v), a flow rate of 0.9 ml/min and a temperature of 25 degrees C. Under these conditions, enantioselective separations were observed for methadone (alpha=1.30) and EDDP (alpha=1.17) within 15 min. Met, EDDP, D3-Met and D3-EDDP were detected using selected ion monitoring at m/z 310.20, 278.20, 313.20 and 281.20, respectively. Linear relationships between peak height ratio and drug-enantiomer concentrations were obtained for methadone in the range of 5.0-600.0 ng/ml, and for EDDP from 0.5 to 15.0 ng/ml per enantiomer with correlation coefficients better than 0.9994, where lower limit of quantification (LLOQ) for Met was 5 ng/ml and for EDDP 0.5 ng/ml. Acceptable intra- and inter-day precision of the method (CVs<4.0%) and accuracy (CVs<4.0%) were obtained. These findings demonstrate the accuracy and precision of the method used to successfully analyze saliva obtained from patients enrolled in a methadone-maintenance program.

Chiral separation of methadone, 2-ethylidene- 1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) and 2-ethyl-5-methyl-3,3-diphenyl-1-pyrroline (EMDP) by capillary electrophoresis using cyclodextrin derivatives

A stereoselective method was developed for the simultaneous determination of methadone and its two major metabolites, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) and 2-ethyl-5-methyl-3,3-diphenyl-1-pyrroline (EMDP) by capillary electrophoresis. Five beta-cyclodextrin (betaCD) background electrolyte (BGE) additives were evaluated for resolution efficiency. The conditions for baseline resolution of each of the three enantiomer pairs was determined to be 1 mM heptakis-(2,6-di-O-methyl)-beta-cyclodextrin (DMbetaCD) in 100 mM phosphate at pH 2.6. This method represents the first successful method for the resolution of the six enantiomers associated with the metabolism of methadone. The utilisation of doubly coated capillaries in conjunction with betaCD derivatives for a faster separation of the methadone-related enantiomers is also reported. The coated capillaries were prepared using a polycation of poly(diallyldimethylammonium chloride) (PDDAC) and a polyanion of dextran sulfate. Baseline resolution of the methadone enantiomers was achieved with a BGE of 8 mM (2-hydroxy)propyl-beta-cyclodextrin (HPbetaCD) in 100 mM phosphate at pH 2.6. The migration times for the stereoselective methadone separation were approximately 4 min, which represented a reduction by a factor of approximately three, compared to that attained using analogous conditions with the uncoated capillary.

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.

Automated LC-MS Method for the Fast Stereoselective Determination of Methadone in Plasma

Methadone (MTD) is a chiral drug widely used for the treatment of opioid dependence for which a rapid analytical method for the determination of each enantiomer would be advantageous. In order to improve method sensitivity and to automate the entire analytical process, a column-switching configuration has been developed. An online extraction system coupled to a cellulose-based chiral stationary phase (CSP), namely Chiralcel OJ-R, was used and detection was performed by mass spectrometry. Fifty microl of plasma were injected into the liquid chromatography-mass spectrometry (LC-MS) system after addition of acetonitrile (ACN) containing methadone deuterated D9 (MTD-D9) (internal standard) and centrifugation. For the rapid extraction step, a large particle size support was selected. A baseline separation of MTD enantiomers was obtained in less than 12 min. Trueness and precision were evaluated with control samples at 500 ng/ml of (R,S)-methadone. Trueness values were 106.6% and 103.0% for (R)-MTD and (S)-MTD, respectively, with a coefficient of variation inferior to 2.5% for both compounds. Finally, a good concordance was found using this method for analysis of plasma samples from patients in maintenance treatment as compared to a previously described HPLC-UV method after liquid-liquid extraction.

Separation of oxazepam, lorazepam, and temazepam enantiomers by HPLC on a derivatized cyclodextrin-bonded phase: application to the determination of oxazepam in plasma

The enantioselective high-performance liquid chromatography (HPLC) of three racemic 3-hydroxybenzodiazepines, oxazepam (Oxa), lorazepam (Lor), and temazepam (Tem), is a difficult operation because of the spontaneous chiral inversion in polar solvent. To solve this problem, we have developed an HPLC method based on a chiral Cyclobond I-2000 RSP column, maintained at 12 degrees C, and a reversed mobile phase (acetonitrile in 1% triethylamine acetate buffer, TEAA) at a flow rate of 0.4 ml/min. Peaks were detected by a photodiode-array detector at 230 nm for quantification and by an optical rotation detector for identification of (+) and (-) enantiomers. The results showed that peak resolutions of Oxa, Lor, and Tem enantiomers, analyzed under the same conditions, were 3.2, 2.0, and 1.8, respectively. For the determination of Oxa enantiomers in plasma of rabbits, extraction with diethyl ether at pH 1.5, a polar organic mobile phase, and a Cyclobond I-2000 SP column were used. Other analytical conditions were the same as previously described. Blood samples were immediately cooled at 4 degrees C and centrifuged at 0 degrees C for the collection of plasma. The results showed a difference in plasma S(+)- and R(-)-oxazepam concentrations in rabbits. No racemization of S(+)- or R(-)-Oxa enantiomers, added alone to blank plasma, was observed after extraction and enantioselective HPLC analysis.

Selective antibodies to methadone enantiomers: synthesis of (R)- and (R,S)-methadone conjugates and determination by an immunoenzymatic method in human serum

Selective antibodies to (R)-methadone (Mtd) and to its racemate were produced in rabbits by immunization with conjugates of (R)- or (R,S)-hemisuccinyl-methadol-bovine serum albumin, respectively. A hapten was first prepared by reduction of (R)- or (R,S)-Mtd with sodium borohydride, followed by esterification with succinic anhydride. The conjugation of hapten with albumin was achieved by the mixed anhydride method. After immunization of rabbits, the titers and specificity of each antibody were determined by ELISA. The antibodies obtained were tested with (R)-, (S)-, (R,S)-Mtd, its major metabolite (EDDP), and some drugs of abuse (morphine, codeine, cocaine). The sensitivities of antibodies to (R)- and (R,S)-Mtd were about 1 and 2 ng/ml, respectively. Selective (R)-antibodies recognized (R)-Mtd about 40 times more avidly than the (S)-isomer, while an antiserum against (R,S)-Mtd recognized (R)- and (S)-isomers to about the same degree. Both selective antibodies showed little interference (about 0.5%) with EDDP metabolite and no crossreactivity with morphine, codeine, and cocaine. These two selective antibodies were used to develop an immunoenzymatic method (ELISA) for the determination of (R)- and (R,S)-Mtd in serum samples of patients under maintenance treatment for narcotic addiction.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Development and application of a chiral high performance liquid chromatography assay for pharmacokinetic studies of methadone

Methadone enantiomers and EDDP, the main metabolite of methadone, were separated (R(s) = 2.0 for methadone enantiomers) following liquid-liquid extraction from human serum and urine followed by reverse-phase high-performance liquid chromatography on a derivatized beta-cyclodextrin column and quantified at therapeutic concentrations with ultraviolet detection. Detector response was linear (r(2) > 0.98) to 1,000 and 2,500 ng x mL(-1) for methadone enantiomers and EDDP, respectively. The limit of quantification from a 1-mL biological sample was 2.5 and 5 ng x mL(-1) for methadone enantiomers and EDDP, respectively. Interday variation was <13% and intraday variation was <8% for the analytes of interest. The assay was applied to plasma protein and erythrocyte binding studies and a 96-h pharmacokinetic study in two healthy female volunteers following oral dosing with rac-methadone. The binding of methadone to plasma proteins was enantioselective with the active (-)-(R) enantiomer having the highest free fraction (mean +/- SD: 21.2+/-7.6% vs. 13.3+/-6.2% for (+)-(S)-methadone, n = 8). Binding of methadone to erythrocytes was not apparently enantioselective (38.6+/-1.3% and 38.1+/-1.4% bound for (-)-(R)- and (+)-(S)-methadone, respectively). The pharmacokinetic study revealed enantioselective disposition of methadone in one volunteer but not in the other. EDDP was observed in urine but was only in small or undetectable concentrations in serum. The method is applicable to in vitro and pharmacokinetic studies of rac-methadone disposition in humans.

Stereoselective quantification of methadone and its major oxidative metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine, in human urine using high-performance liquid chromatography

A stereoselective HPLC assay was developed for the quantification of the enantiomers of methadone and its major oxidative metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in human urine. The compounds were quantified in a single assay following liquid-liquid extraction and stereoselective HPLC with UV detection. Calibration curve concentrations ranged from 0.125 to 12.5 microM for each enantiomer. Assay performance was assessed using quality control samples, and the inter- and intra-assay bias (<10%) and precision (<15%) were acceptable for all compounds. The assay was successfully used to quantitate the enantiomers of methadone and EDDP in urine samples obtained from subjects receiving methadone maintenance therapy.

Chiral stationary phases in HPLC for the stereoselective determination of methadone

An extensive study of the behavior of three chiral stationary phases (CSP) is presented for the stereoselective determination of methadone. The following chromatographic columns were selected: a cellulose, Chiralcel OJ; a modified cyclodextrin. Cyclobond I 2000 RSP, and a protein, Chiral-AGP. Retention factors, enantioselectivity, efficiency, and resolution were tested by modifying the composition of the mobile phase as well as the temperature. The mechanism for the chiral recognition of methadone on each support was discussed. Optimal chromatographic parameters were obtained for the three supports tested, and methadone enantiomers were separated in less than 20 minutes. The cellulose-based column gave the best resolution, but this CSP was not adapted to clinical analyses of methadone. Under optimized conditions, the cyclodextrin- and protein-based columns allowed an excellent separation of methadone enantiomers, but no interference with the primary metabolite was found only with Chiral-AGP.

Enantioselective analysis of methadone in saliva by liquid chromatography-mass spectrometry

Saliva was tested and evaluated as a biological matrix for methadone (Mtd) monitoring. Conventional method using a narrow bore C18 column, and an enantioselective method using a narrow bore alpha1-acid glycoprotein column, were developed using liquid chromatography coupled with a mass spectromeric (MS) detector. After optimisation of MS conditions by flow injection analysis, selected ion monitoring detection was used to enhance sensitivity. The total Mtd concentration and the enantiomeric ratio in saliva were validated using an experimental design. The methods were applied to samples provided by heroin addicts undergoing a Mtd treatment. Results on total Mtd determination showed a very poor correlation between saliva and serum, whereas the enantiomeric ratios of Mtd gave a very good one.

Development of validated stereoselective methods for methadone determination in clinical samples

A stereoselective analysis of methadone (Mtd) in whole blood and serum was developed using liquid chromatography on a protein based chiral stationary phase. Liquid-liquid extraction (LLE) and solid phase extraction methods were applied before chromatographic analysis. The extraction procedure, as well as the choice of the biological matrix, showed significant differences in the extraction yield and in the precision of the assays. Serum was selected for this assay and LLE was chosen as the preparation step because of its simplicity and rapidity. The total procedure was validated and applied to clinical samples. Samples taken from 45 heroin-addicted patients were analyzed. A correlation was found between the dose administered and Mtd concentration (total and R-form), but interindividual variability of the total normalized Mtd was seen (concentration varied from 90 to 530 ng/ml). Furthermore, two populations were apparently observed with a mean Mtd concentration of 200 and 475 ng/ml, respectively. Stereoselective analyses showed that more than 50% of the patients presented a nonracemic ratio, and particularly about 25% showed a preferential metabolism of the active R-Mtd enantiomer. Therefore, the stereoselective determination of Mtd is necessary to improve the quality of the treatment of heroin addiction.

Novel high-performance liquid chromatographic and solid-phase extraction methods for quantitating methadone and its metabolite in spiked human urine

A novel solid-phase extraction (SPE) method and HPLC method were developed for the determination of methadone and its metabolite from spiked human urine. For sample cleanup, a spiked urine sample was pretreated with phosphoric acid followed by a well-thought-out SPE method using a 10-mg Oasis HLB 96-well extraction plate. In this SPE method, the concentration of methanol as well as the pH are optimized to preferentially isolate the analytes of interest from the sample matrix. Low elution volumes (200 microl) are achieved; this eliminates evaporation and reconstitution of the sample solution. Recoveries from human urine matrix were greater than 91% with RSD values less than 4.5%. For the HPLC analysis, the separation was obtained using a SymmetryShield RP18 column with a mobile phase of 0.1% TFA-methanol (60:40, v/v). Good peak shapes were obtained without the need of addition of any competing reagent to the mobile phase. Additionally, significant signal-to-noise enrichment was achieved by diluting the final SPE eluates four-fold with water.

Enantioselective high-performance liquid chromatographic method for the determination of methadone and its main metabolite in urine using an AGP and a C8 column coupled serially

A simple and sensitive method for the enantioselective high-performance liquid chromatographic determination of methadone and its main metabolite, EDDP, in human urine is described. (-)-(R)-Methadone, (+)-(S)-methadone, (+)-(R)-EDDP, (-)-(S)-EDDP and imipramine as an internal standard are detected by ultraviolet detection at 200 nm. The enantiomers of methadone and EDDP were extracted from human urine by a simple liquid-liquid extraction procedure. The extracted sample was reconstructed in mobile phase and the enantiomers of methadone and EDDP were quantitatively separated by HPLC on a short analytical LiChrospher RP8 column coupled in series with a chiral AGP column. Determination of all four enantiomers was possible in the range of 0.03 to 2.5 microM. The recoveries of methadone enantiomers and EDDP enantiomers added to human urine were about 90% and 80%, respectively. The method was applicable for determination of methadone enantiomers and the enantiomers of its main metabolite in urine samples from methadone maintenance patients and patients suffering from severe chronic pain.

Rapid determination of methadone and its major metabolite in biological fluids by gas-liquid chromatography with thermionic detection for maintenance treatment of opiate addicts

A rapid gas-liquid chromatographic assay is developed for the quantification of methadone (Mtd) and its major metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), in biological fluids of opiate addicts. After alkaline extraction from samples with lidocaine hydrochloride as internal standard, Mtd and EDDP are separated on SP-2250 column at 220 degrees C and detected with a thermionic detector. The chromatographic time is about 6 min. The relative standard deviations (R.S.D.) of Mtd and EDDP standards are between 1.5 and 5.5%. Most drugs of abuse (morphine, codeine, narcotine, cocaine, benzoylecgonine, cocaethylene, dextropropoxyphene etc) are shown not to interfere with this technique. The method has been applied to study the levels of Mtd and EDDP metabolite in serum, saliva and urine of patients under maintenance treatment for opiate dependence. EDDP levels were found higher than those of Mtd in urine samples from four treated patients, but lower in serum and undetectable in saliva. However, Mtd concentrations were higher in saliva than in serum.