Method development and validation for quantitative determination of methadone enantiomers in human plasma by liquid chromatography/tandem mass spectrometry1

A genetic-based population PK/PD modeling of methadone in Chinese opiate dependence patients

PURPOSE

The full potential of methadone maintenance treatment (MMT) is often limited by the large inter-individual variability in both pharmacokinetics (PK) and pharmacodynamics (PD), and by the risk of torsade de pointes, a severe adverse effect caused by QTc prolongation. The current study aims to quantitate the contribution of genetic polymorphisms and other variables in PK/PD variability, and their contribution to the QTc interval prolongation in Chinese MMT patients.

METHODS

Population PK models were developed to fit (R)- and (S)-methadone PK data. Hierarchical models were tested to characterize the PK profile, the concentration-QTc relationship, and concentration-urinalysis illicit drug testing relationship, with demographics and genetic variants being included as covariates. Simulation based on the developed PK/PD models was performed to assess the effect of methadone dose and genetic variants on QTc interval prolongation.

RESULTS

The PK data were best-fit by a one-compartment, first-order absorption model. Clearance of (R)- and (S)-methadone was both affected by the weighted activity score derived from genetic variants. A linear model was used to describe both the methadone concentration-urinalysis illicit drug testing relationship and the methadone concentration-QTc relationship. Concentration of (R)- and (S)-methadone exhibits a comparable effect on QTc prolongation. Simulation showed that the percentage of QTc higher than 450 ms was almost doubled in the lowest clearance group as compared the highest when methadone dose was greater than 120 mg.

CONCLUSIONS

The large variability in PK/PD profiles can be partially explained by the genetic variants in an extent different from other population, which confirmed the necessity to conduct such a study in the specific Chinese patients.

Effect of HIV, antiretrovirals, and genetics on methadone pharmacokinetics: Results from the methadone antiretroviral pharmacokinetics study

BACKGROUND

Methadone treatment of opioid use disorder in HIV-infected individuals is complicated by drug-drug interactions. Genetic and other cofactors further contribute to interindividual variability in methadone pharmacokinetics. We used population pharmacokinetics to estimate the effect of drug-drug interactions, genetics, and other cofactors on methadone pharmacokinetics in a methadone maintained population in Vietnam.

METHODS

Plasma R- and S-methadone levels were measured in 309 methadone maintained individuals just before and 2-5 h following methadone dosing. A linear one-compartment population pharmacokinetic model with first-order conditional estimation with interaction was used to evaluate methadone clearance (CL/F) and volume of distribution (V/F). The influence of covariates on parameter estimates was evaluated using stepwise covariate modeling. Covariates included HIV status, antiretroviral use (efavirenz or nevirapine), weight, BMI, age, methadone dose, and 8 single nucleotide polymorphisms in across the CYP2B6, ABCB1, and NR1I3 genes.

RESULTS

Taking either efavirenz or nevirapine increased R-methadone CL/F 220%. Nevirapine and efavirenz increased S-methadone CL/F by 404% and 273%, respectively. Variants in NR1I3 increased R- and S-methadone CL/F by approximately 20% only in patients taking efavirenz. Different alleles in ABCB1 rs2032582 either increased or decreased R-methadone CL/F by 10%. The CYP 2B6*4 variant decreased S-methadone CL/F by 18%. HIV-infection increased R- and S-methadone CL/F and V/F by 24%-39%.

CONCLUSIONS

The HIV antiretrovirals nevirapine and efavirenz significantly increase methadone clearance. Variants inNR1I3 increased the effect of efavirenz on methadone clearance. Other variants affecting methadone CL/F were also confirmed. To our knowledge, this is the first report of HIV itself affecting methadone pharmacokinetics.

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.

In silico ordinary differential equation/partial differential equation hemodialysis model estimates methadone removal during dialysis

Background

There is a need to have a model to study methadone’s losses during hemodialysis to provide informed methadone dose recommendations for the practitioner.

Aim

To build a one-dimensional (1-D), hollow-fiber geometry, ordinary differential equation (ODE) and partial differential equation (PDE) countercurrent hemodialyzer model (ODE/PDE model).

Methodology

We conducted a cross-sectional study in silico that evaluated eleven hemodialysis patients. Patients received a ceiling dose of methadone hydrochloride 30 mg/day. Outcome measures included: the total amount of methadone removed during dialysis; methadone’s overall intradialytic mass transfer rate coefficient, k_m; and, methadone’s removal rate, j_ME. Each metric was measured at dialysate flow rates of 250 mL/min and 800 mL/min.

Results

The ODE/PDE model revealed a significant increase in the change of methadone’s mass transfer with increased dialysate flow rate, %Δk_m=18.56, P=0.02, N=11. The total amount of methadone mass transferred across the dialyzer membrane with high dialysate flow rate significantly increased (0.042±0.016 versus 0.052±0.019 mg/kg, P=0.02, N=11). This was accompanied by a small significant increase in methadone’s mass transfer rate (0.113±0.002 versus 0.014±0.002 mg/kg/h, P=0.02, N=11). The ODE/PDE model accurately predicted methadone’s removal during dialysis. The absolute value of the prediction errors for methadone’s extraction and throughput were less than 2%.

Conclusion

ODE/PDE modeling of methadone’s hemodialysis is a new approach to study methadone’s removal, in particular, and opioid removal, in general, in patients with end-stage renal disease on hemodialysis. ODE/PDE modeling accurately quantified the fundamental phenomena of methadone’s mass transfer during hemodialysis. This methodology may lead to development of optimally designed intradialytic opioid treatment protocols, and allow dynamic monitoring of outflow plasma opioid concentrations for model predictive control during dialysis in humans.

Ethnic and genetic factors in methadone pharmacokinetics: a population pharmacokinetic study

BACKGROUND

Treatment of opiate use disorders with methadone is complicated by wide interindividual variability in pharmacokinetics. To identify potentially contributing covariates in methadone pharmacokinetics, we used population pharmacokinetic modeling to estimate clearance (CL/F) and volume of distribution (V/F) for each methadone enantiomer in an ethnically diverse methadone maintained population.

METHODS

Plasma levels of the opiate-active R-methadone and opiate-inactive S-methadone were measured in 206 methadone maintained subjects approximately two and twenty-three hours after a daily oral dose of rac-methadone. A linear one-compartment population pharmacokinetic model with first-order conditional estimation with interaction (FOCE-I) was used to evaluate methadone CL/F and V/F. The influence of covariates on parameter estimates was evaluated using stepwise covariate modeling. Covariates included ethnicity, gender, weight, BMI, age, methadone dose, and 21 single nucleotide polymorphisms in genes implicated in methadone pharmacokinetics.

RESULTS

In the final model, for each enantiomer, Hmong ethnicity reduced CL/F by approximately 30% and the rs2032582 (ABCB1 2677G>T/A) GG genotype was associated with a 20% reduction in CL/F. The presence of the rs3745274 minor allele (CYP2B6 515G>T) reduced CL/F by up to 20% for S-methadone only. A smaller effect of age was noted on CL/F for R-methadone.

CONCLUSION

This is the first report showing the influence of the rs2032582 and rs3745274 variants on methadone pharmacokinetics rather than simply dose requirements or plasma levels. Population pharmacokinetics is a valuable method for identifying the influences on methadone pharmacokinetic variability.

Quantitation of methadone and metabolite in patients under maintenance treatment

Gas chromatography-mass spectrometry quantitative method was developed to monitor concentrations of methadone and its metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in plasma and urine of patients. The developed method was simple, accurate and reproducible to quantify methadone and EDDP in plasma and urine samples in the concentration range of 15-1,000 and 50-2,000 ng/mL, respectively. The proposed analytical method was applied to plasma and urine samples obtained from 96 patients undergoing methadone maintenance treatment (MMT) with daily methadone doses of 2-120 mg/day. Urinary methadone excretion was observed to be significantly affected by pH, in which the ratio of methadone to EDDP was two times higher in acidic urine (P = 0.029). The findings of this study further enhance the guidelines for monitoring of methadone treatment among outpatients. Methadone-to-EDDP ratio in urine was found to be consistent at 24 and 4 h, hence suggesting the possibility that outpatients may be monitored with single urine sample in order to check for compliance. This study which provides data on peak concentrations of methadone and EDDP as well as the ratio of both compounds has added to the body of knowledge regarding pharmacokinetic properties of methadone among heroin-dependent patients under MMT.

Optimization of solvent bar microextraction combined with gas chromatography for preconcentration and determination of methadone in human urine and plasma samples

In this study, solvent bar microextraction combined with gas chromatography-flame ionization detector (GC-FID) was used for preconcentration and determination of methadone in human body fluids. The target drug was extracted from an aqueous sample with pH 11.5 (source phase) into an organic extracting solvent (1-Undecanol) located inside the pores and lumen of a polypropylene hollow fiber as a receiving phase. To obtain high extraction efficiency, the effect of different variables on the extraction efficiency was studied using an experimental design. The variables of interest were the organic phase type, source phase pH, ionic strength, stirring rate, extraction time, concentration of Triton X-100, and extraction temperature, which were first investigated by Plackett-Burman design and subsequently by central composite design (CCD). So that the optimum experimental condition was obtained when the sodium chloride concentration was 5% (w/v); stirring rate, 700 rpm; extraction temperature, 20 °C; extraction time, 45 min and pH of the aqueous sample, 11.5. Under the optimized conditions, the preconcentration factors were between 275 and 300. The calibration curves were linear in the concentration range of 10-1500 μg L(-1). The limits of detection (LODs) were 2.7-7 and relative standard deviations (RSDs) of the proposed method were 5.9-7.3%. Ultimately, the applicability of the current method was evaluated by the extraction and determination of methadone in different biological samples.

Validation of a LC–APCI-MS/MS method for quantification of methadone, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) and 2-ethyl-5-methyl-3,3-diphenylpyraline (EMDP) in infant plasma following protein precipitation

A validated, quantitative LC-APCI-MS/MS method for methadone, EDDP and EMDP in 200-microL plasma is presented. Specimen preparation was limited to protein precipitation and centrifugation. Chromatographic separation was achieved on a Synergi Hydro-RP 80A (50 mm x 2.0 m, 4 microm) column with gradient elution. The assay was linear from 1 to 500 ng/mL, with intra- and inter-assay accuracy >or=87.5% and intra- and inter-assay precision <13.4% R.S.D. and recovery >or=87.5% for all analytes at 40 ng/mL. This analytical method is suitable for the accurate and precise determination of methadone and metabolites in human plasma specimens.

Enantioselective determination of azelnidipine in human plasma using liquid chromatography–tandem mass spectrometry

A sensitive and simple method was developed for determination of the enantiomers of azelnidipine, (R)-(-)-azelnidipine and (S)-(+)-azelnidipine, in human plasma using chiral liquid chromatography with positive ion atmospheric pressure chemical ionization tandem mass spectrometry. Plasma samples spiked with stable isotope-labeled azelnidipine, [(2)H(6)]-azelnidipine, as an internal standard, were processed for analysis using a solid-phase extraction in a 96-well plate format. The azelnidipine enantiomers were separated on a chiral column containing alpha(1)-acid glycoprotein as a chiral selector under isocratic mobile phase conditions. Acquisition of mass spectrometric data was performed in multiple reaction monitoring mode, monitoring the transitions from m/z 583-->167 for (R)-(-)-azelnidipine and (S)-(+)-azelnidipine, and from m/z 589-->167 for [(2)H(6)]-azelnidipine. The standard curve was linear over the studied range (0.05-20 ng/mL), with r(2)>0.997 using weighted (1/x(2)) quadratic regression, and the chromatographic run time was 5.0 min/injection. The intra- and inter-assay precision (coefficient of variation), calculated from the assay data of the quality control samples, was 1.2-8.2% and 2.4-5.8% for (R)-(-)-azelnidipine and (S)-(+)-azelnidipine, respectively. The accuracy was 101.2-117.0% for (R)-(-)-azelnidipine and 100.0-107.0% for (S)-(+)-azelnidipine. The overall recoveries for (R)-(-)-azelnidipine and (S)-(+)-azelnidipine were 71.4-79.7% and 71.7-84.2%, respectively. The lower limit of quantification for both enantiomers was 0.05 ng/mL using 1.0 mL of plasma. All the analytes showed acceptable short-term, long-term, auto-sampler and stock solution stability. Furthermore, the method described above was used to separately measure the concentrations of the azelnidipine enantiomers in plasma samples collected from healthy subjects who had received a single oral dose of 16 mg of azelnidipine.

Bioavailability of triple-bead mixed amphetamine salts compared with a dose-augmentation strategy of mixed amphetamine salts extended release plus mixed amphetamine salts immediate release

OBJECTIVE

To compare the single-dose pharmacokinetics of triple-bead mixed amphetamine salts (MAS), an oral, once-daily, enhanced extended-release amphetamine formulation, with MAS extended release (MAS XR) (Adderall XR) + MAS immediate release (MAS IR) administered 8 h later.

METHODS

This was a phase I, randomized, open-label, single-dose, single-center, two-period, crossover study in healthy adult volunteers designed to evaluate the bioavailability of triple-bead MAS over the course of a full day. Subjects were randomized to triple-bead MAS 37.5 mg or MAS XR 25 mg + MAS IR 12.5 mg administered 8 h later (MAS XR + MAS IR). The reference treatment was designed to mimic the clinical practice of providing extended coverage by supplementing a morning dose of MAS XR with a dose of MAS IR 8 h later in order to increase the duration of action. Plasma was assayed for d-amphetamine and l-amphetamine. Treatment-emergent adverse events (TEAEs), vital signs, electrocardiograms (ECGs), and laboratory data were also collected for safety evaluation.

RESULTS

Exposure to d- and l-amphetamine was equivalent between triple-bead MAS and MAS XR + MAS IR based on maximum plasma concentration (Cmax) and area under the plasma concentration-time curve from time 0 to infinity (AUC(0-infinity)). For Cmax, least-squares mean ratios comparing triple-bead MAS with MAS XR + MAS IR were 101.0% and 90.9% for d-amphetamine and l-amphetamine, respectively, and for AUC(0-infinity) were 104.4% and 95.3% for d-amphetamine and l-amphetamine, respectively. Median time to maximum observed plasma concentration (Tmax) values for d-amphetamine and l-amphetamine were 8.0 h for triple-bead MAS and 10.0 h for MAS XR + MAS IR. There were no clinically meaningful differences between the study formulations for TEAEs or laboratory values. One subject experienced an ECG abnormality (asymptomatic premature ventricular contractions) leading to early termination from the study.

CONCLUSIONS

In healthy adults, the exposure observed with triple-bead MAS 37.5 mg was bioequivalent to MAS XR 25 mg supplemented by MAS IR 12.5 mg administered 8 h later. These data demonstrate that a single morning dose of triple-bead MAS provides equivalent plasma concentrations to those observed with a dose-augmentation strategy of MAS XR in the morning followed by MAS IR in the afternoon, while minimizing peak-to-trough fluctuations. Triple-bead MAS was also generally well-tolerated in this study.

The effect of multiple doses of peginterferon alfa-2b on the steady-state pharmacokinetics of methadone in patients with chronic hepatitis C undergoing methadone maintenance therapy

This multicenter, open-label study evaluated the effects of multiple doses of peginterferon alfa-2b on the steadystate pharmacokinetics of methadone in 20 adults with hepatitis C virus infection who were enrolled in a methadone maintenance program. All subjects received peginterferon alfa-2b 1.5 mug/kg/wk for 4 weeks and maintained their normal methadone regimen. Serial blood samples were collected immediately before the first and after the fourth peginterferon alfa-2b dose (day 23). At day 23, exposure to the active methadone R-enantiomer increased by approximately 15% following administration of peginterferon alfa-2b, with 90% confidence intervals just outside the bioequivalence criteria (range, 80%-125%). Similar increases in exposure (C(max), AUC(0-24), and AUC(last)) were observed with S-methadone and total methadone. Peginterferon alfa-2b was well tolerated. Peginterferon alfa-2b is associated with minor increases in exposure to methadone in individuals with hepatitis C virus infection; however, these increases are unlikely to be clinically meaningful and are not associated with any safety concerns.

Simultaneous determination of methadone, buprenorphine and norbuprenorphine in biological fluids for therapeutic drug monitoring purposes

Methadone and buprenorphine are two of the drugs most frequently used for abstinence from illicit opioids and in the treatment of pain. A sensitive and selective high-performance liquid chromatographic method with diode array detection for the simultaneous determination of methadone, buprenorphine and norbuprenorphine has been developed. Separation of the three analytes was obtained by using a reversed-phase column (C8, 250mmx4.6mm i.d., 5microm) and a mobile phase composed of 40% phosphate buffer containing triethylamine, 50% methanol and 10% acetonitrile (final apparent pH 6.0). Loxapine was used as the internal standard. An accurate pre-treatment procedure of biological samples was developed, using solid-phase extraction with C8 cartridges (100mg, 1mL) and needing small amounts of plasma or urine (300microL). The calibration curves were linear over a working range of 10.0-1500.0ng/mL for methadone and of 5.0-500.0ng/mL for buprenorphine and norbuprenorphine in both matrices. The limit of quantitation (LOQ) and the limit of detection (LOD) were 1.0 and 0.4ng/mL for methadone and 0.5 and 0.2ng/mL for both buprenorphine and norbuprenorphine, respectively. The method was successfully applied to the analysis of plasma and urine samples from patients undergoing treatment with these drugs. Precision and accuracy results were satisfactory and no interference from endogenous or exogenous compounds was found. The method is suitable for the simultaneous determination of methadone and buprenorphine in human plasma and urine for therapeutic drug monitoring purposes.

Simultaneous determination of psychoactive drugs and their metabolites in aqueous matrices by liquid chromatography mass Spectrometry

A multi-residue method was developed that allows for the simultaneous determination of psychoactive compounds such as opioids, tranquilizers, antiepileptics (primidone, carbamazepine plus two metabolites),the cocaine metabolite benzoylecgonine, the antidepressant doxepin, as well as the calcium channel blocker verapamil in raw and treated wastewater, surface water, groundwater, and drinking water. After solid-phase extraction with Oasis HLB at neutral pH, the analytes were detected by LC electrospray tandem MS in the positive ion mode. With a few exceptions relative recoveries of the analytes exceeded 70%. The limits of quantification were in the low ng/L range. Matrix effects were compensated by using appropriate deuterated or 13C-15N-labeled surrogate standards. For raw and treated wastewater, concentration factors were lowered to reduce matrix effects. Most analytes (15 of 20) were found in raw and treated wastewater as well as in surface water, and hence, are presumably ubiquitously present in the environment. Antiepileptics, the opium alkaloids morphine and codeine, dihydrocodeine, the two tranquilizers oxazepam and temazepam, the opioid tramadol, doxepin, and verapamil were detected in STP discharges and German rivers at concentrations up to the microg/L range. In drinking water, only carbamazepine, its metabolite 10,11-dihydroxy-10,11-dihydrocarbamazepine, and primidone were present at concentrations up to 0.020 microg/L.

An automated and fully validated LC-MS/MS procedure for the simultaneous determination of 11 opioids used in palliative care, with 5 of their metabolites

A fully validated liquid chromatographic procedure coupled with electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) is presented for quantitative determination of the opioids buprenorphine, codeine, fentanyl, hydromorphone, methadone, morphine, oxycodone, oxymorphone, piritramide, tilidine, and tramadol together with their metabolites bisnortilidine, morphine-glucuronides, norfentanyl, and nortilidine in blood plasma after an automatically performed solid-phase extraction (SPE). Separation was achieved in 35 min on a Phenomenex C12 MAX-RP column (4 microm, 150 x 2 mm) using a gradient of ammonium formiate buffer (pH 3.5) and acetonitrile. The validation data were within the required limits. The assay was successfully applied to authentic plasma samples, allowing confirmation of the diagnosis of overdose situations as well as monitoring of patients' compliance, especially in patients under palliative care.

Liquid separation techniques coupled with mass spectrometry for chiral analysis of pharmaceuticals compounds and their metabolites in biological fluids

Determination of the chiral composition of drugs is nowadays a key step in order to determine purity, activity, bioavailability, biodegradation, etc., of pharmaceuticals. In this article, works published for the last 5 years on the analysis of chiral drugs by liquid separation techniques coupled with mass spectrometry are reviewed. Namely, chiral analysis of pharmaceuticals including, e.g., antiinflammatories, antihypertensives, relaxants, etc., by liquid chromatography-mass spectrometry and capillary electrophoresis-mass spectrometry are included. The importance and interest of the analysis of the enantiomers of the active compound and its metabolites in different biological fluids (plasma, urine, cerebrospinal fluid, etc.) are also discussed.

Applicability of bioanalysis of multiple analytes in drug discovery and development: review of select case studies including assay development considerations

The development of sound bioanalytical method(s) is of paramount importance during the process of drug discovery and development culminating in a marketing approval. Although the bioanalytical procedure(s) originally developed during the discovery stage may not necessarily be fit to support the drug development scenario, they may be suitably modified and validated, as deemed necessary. Several reviews have appeared over the years describing analytical approaches including various techniques, detection systems, automation tools that are available for an effective separation, enhanced selectivity and sensitivity for quantitation of many analytes. The intention of this review is to cover various key areas where analytical method development becomes necessary during different stages of drug discovery research and development process. The key areas covered in this article with relevant case studies include: (a) simultaneous assay for parent compound and metabolites that are purported to display pharmacological activity; (b) bioanalytical procedures for determination of multiple drugs in combating a disease; (c) analytical measurement of chirality aspects in the pharmacokinetics, metabolism and biotransformation investigations; (d) drug monitoring for therapeutic benefits and/or occupational hazard; (e) analysis of drugs from complex and/or less frequently used matrices; (f) analytical determination during in vitro experiments (metabolism and permeability related) and in situ intestinal perfusion experiments; (g) determination of a major metabolite as a surrogate for the parent molecule; (h) analytical approaches for universal determination of CYP450 probe substrates and metabolites; (i) analytical applicability to prodrug evaluations-simultaneous determination of prodrug, parent and metabolites; (j) quantitative determination of parent compound and/or phase II metabolite(s) via direct or indirect approaches; (k) applicability in analysis of multiple compounds in select disease areas and/or in clinically important drug-drug interaction studies. A tabular representation of select examples of analysis is provided covering areas of separation conditions, validation aspects and applicable conclusion. A limited discussion is provided on relevant aspects of the need for developing bioanalytical procedures for speedy drug discovery and development. Additionally, some key elements such as internal standard selection, likely issues of mass detection, matrix effect, chiral aspects etc. are provided for consideration during method development.

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.

Determination of free and protein-bound methadone and its major metabolite EDDP: Enantiomeric separation and quantitation by LC/MS/MS

OBJECTIVE

To measure free and protein-bound R- and S-enantiomers of methadone and its major metabolite, 2-ethylidine-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in serum.

METHODS

To determine free fraction, samples were filtered using ultrafiltration membranes with a molecular weight cut-off of 10,000 Da and extracted using liquid-liquid extraction. The solvent extract was evaporated and reconstituted in mobile phase for analysis by LC/MS/MS. Total analyte was determined by extracting unfiltered samples. Enantiomeric separation was by chiral chromatography.

RESULTS

LC conditions resulted in baseline separation of R- and S-EDDP, and 85% resolution of methadone enantiomers. Precision of spiked specimens for both R- and S-methadone and R- and S-EDDP was less than 10% at 100 nM, and did not exceed 20% at 10 nM.

CONCLUSIONS

Using minimal sample clean-up and a total instrument run-time of 10 min, a rapid, sensitive and highly specific method was developed for quantitation of free and total R- and S-enantiomers of methadone and EDDP.

Surfactant enhanced liquid-phase microextraction of basic drugs of abuse in hair combined with high performance liquid chromatography

The aim of this study was to evaluate the performance of a technique for simultaneous testing of hydrophilic abuse drugs in hair. The analysis of, codeine and methadone in morphine hair included incubation in methanol (5h, 50 degrees C), Surfactant enhanced liquid-phase microextraction (SE-LPME) and HPLC analysis. This study has demonstrated that SE-LPME constitute a real alternative to the other liquid-phase microextraction methods, for pre-concentration and extraction of hydrophilic drugs in biological samples and has shown the advantages of these optimized methodologies over the traditional microextraction techniques. For these drugs recoveries in the range of 57.5-93.7 were obtained from hair. The drugs were enriched by a factor of 61-128 during SE-LPME. Linearity (r2, 0.9982-0.9997) was obtained in the range of 50-500 microg/l for morphine and 10-500 microg/l for codeine and methadone.

Lack of an effect of atazanavir on steady-state pharmacokinetics of methadone in patients chronically treated for opiate addiction

BACKGROUND

Effective antiretroviral treatment of opiate-addicted drug users with HIV infection often requires concomitant substance abuse treatment, commonly with methadone. Pharmacological interactions between antiretroviral drugs and methadone may result in opiate withdrawal or increased side effects.

OBJECTIVES

To determine if atazanavir, a once-daily protease inhibitor and moderate inhibitor of P450 CYP3A4, exhibited pharmacokinetic interactions with (R)-methadone.

METHODS

Methadone pharmacokinetic parameters were measured in 16 patients on chronic methadone therapy prior to and after 14 days of daily administration of atazanavir. Steady-state pharmacokinetic values for total, (R)- (active) and (S)- (inactive) isomers of methadone were derived from plasma concentrations versus time data. Symptoms of opiate withdrawal and excess were monitored.

RESULTS

For the active isomer (R)-methadone, the ratio of geometric means for coadministration with atazanavir relative to methadone alone were 1.03 [90% confidence interval (CI), 0.95-1.10] for the area under the concentration-time curve (AUC), 0.91 (90% CI, 0.84-1.00) for plasma maximal concentration and 1.11 (90% CI, 1.02-1.20) for plasma trough concentration. Confidence intervals for all three were within the no-effect or bioequivalence range of 0.80-1.25 for (R)-methadone. Inactive (S)-methadone was modestly reduced during atazanavir coadministration. Clinically relevant symptoms of opiate withdrawal or excess were not detected. Exposures to atazanavir were within range of previously reported values.

CONCLUSIONS

No clinically relevant pharmacokinetic interactions were found between atazanavir and methadone. Dosage adjustment need not be recommended for either methadone or atazanavir when co-administered to patients treated for opiate abuse and HIV disease.

Development of a low volume plasma sample precipitation procedure for liquid chromatography/tandem mass spectrometry assays used for drug discovery applications

The demand for high sensitivity bioanalytical methods has dramatically increased in the drug discovery stage; in addition, there has been a growing trend of reducing the sample volume that is required for these assays. A sensitive high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) procedure has been developed and tested to meet these needs. The assay requires only a low plasma sample volume (10 microL) and employs a protein precipitation procedure using a 1:6 plasma/acetonitrile ratio. The supernatant is injected directly into the LC/MS/MS system using the selected reaction monitoring (SRM) procedure for detection. A generic HPLC gradient based on a methanol/water mobile phase with a flow rate set to 0.8 mL/min was used. The test method showed very good linearity between 0.1-1000 ng/mL (R2 = 0.9737), precision (%RSD = 6-9), accuracy (%RE = -2) and reproducibility (%RSD = 11). A drug discovery IV/PO study was assayed using both the new low volume method and our standard volume (50 microL) method. The correlation of the two sets of data from the two methods was excellent (R2 = 0.9287). This new assay procedure has been successfully used in our laboratory for over 100 different rat or mouse discovery PK studies.

Current literature in mass spectrometry

In order to keep subscribers up‐to‐date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (5 Weeks journals ‐ Search completed at 8th. Sept. 2004)

Simultaneous chiral analyses of multiple analytes: case studies, implications and method development considerations

The field of chiral separations had a modest beginning some two decades ago. However, due to rapid technological advancement coupled with simultaneous availability of innovative chiral stationary phases and novel chiral derivatization agents, the field of chiral separations has now totally outpaced many other separation fields. Keeping pace with rapid changes in the field of chiral separations, investigators continue to add stereoselective pharmacokinetic, pharmacodynamic, pharmacologic and toxicological data of new and/or marketed racemic compounds to the literature. Examination of the evolution of chiral separations suggests that in the beginning many investigators attempted to separate and quantify a single pair of enantiomers, adopting either direct (separation made on a chiral stationary phase) or indirect (separation made following precolumn conversion of enantiomers to corresponding diastereomers) approaches. However, more recent trends in chiral separations suggest that investigators are attempting to separate and quantify multiple pairs of enantiomers with available technologies. Added to this, some interesting trends have been observed in many of the recently reported chiral applications, including preferences regarding internal standard selection, mobile phase contents and composition, sorting out issues with mass spectrometric detection, determination of elution order, analytical manipulations of metabolite(s) without reference standards and addressing some specificity-related issues. This review mainly focuses on chiral separations involving multiple chiral analytes and attempts to justify the need for such chiral separations involving multiple analytes. In this context, several cases studies are described on the utility and applicability of such chiral separations under discrete headings to provide an account to the readership on the implications of such tasks. The topics of case studies covered in this review include: (a) therapy markers--differentiation from drug abuse and/or applicability in forensics; (b) role in pharmacogenetic/polymorphic evaluation; (c) monitoring and understanding the role of parent and active metabolite(s) in clinical and preclinical investigations; (d) exploration on the pharmacokinetic utility of an active chiral metabolite vis-a-vis the racemic parent moiety; (e) understanding the chirality play in delineating peculiar toxic effects; (f) exploration of chiral inversion phenomenon, and understanding the role of stereoselective metabolism. For the further benefit of readership, some select examples (n = 19) of the separation of multiple chiral analytes with appropriate information on chromatography, detection system, validation parameters and applicable conclusion are also provided. Finally, the review covers some useful considerations for method development involving multiple chiral analytes.