Development and validation of a LC/MS/MS method for simultaneous quantification of oxcarbazepine and its main metabolites in human serum

Quantification of Oxcarbazepine Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Oxcarbazepine (Trileptal®) has been found effective in the treatment of tonic-clonic seizures and partial seizures with or without secondary generalization, with fewer side effects than traditional therapy. Oxcarbazepine is a keto analogue of carbamazepine. It is rapidly reduced to 10-monohydroxy carbamazepine (MHD), its active metabolite. This assay measures concentrations for oxcarbazepine metabolite (MHD), internal standard (MHD 13C6) solution is added to all the patient specimens resulting in precipitation of proteins. The analytes are separated using a Phenomenex Kinetex C18 column and are detected with a mass spectrophotometer utilizing multiple reaction monitoring (MRM). The analytes are qualitatively identified and quantitated from a calibration curve generated from calibrators included in the run.

Development and Validation of a Highly Sensitive and Rapid LC-MS3 Strategy to Determine Oxcarbazepine and Its Active Metabolite in the Serum of Patients with Epilepsy and Its Application in Therapeutic Drug Monitoring

A sensitive and rapid bioanalytical method based on the LC-triple-stage fragmentation (LC-MS³) strategy on a hybrid triple quadrupole-linear ion trap mass spectrometer in combination with protein precipitation extraction for sample pretreatment has been developed and validated for the simultaneous determination of the antiepileptic drug oxcarbazepine (OXC) and its main active metabolite (MHD) in human serum. The separation was performed on a Waters XBridge BEH C18 column (2.5 µm, 2.1 × 50 mm) in isocratic elution with 0.1% formic acid in water and methanol (50:50, v:v) as the mobile phase. The run time for each sample was 2.0 min. The calibration curves ranging from 25 to 1600 ng/mL for OXC and from 0.5 to 32 μg/mL for MHD showed correlation coefficients (r) better than 0.99. All of the validation data, such as precision, accuracy and other parameters, fit the requirements of the current bioanalytical method validation guidelines. The LC-MS³ method for quantitation of OXC and MHD was compared with the LC-MRM based method. Passing–Bablok regression coefficients and Bland–Altman plots showed that the developed LC–MS³ method is a reliable method for quantitative analysis of OXC and MHD. The proposed LC-MS³ method was successfully applied to determine the serum concentrations of OXC and MHD to support a clinical study.

Simultaneous Determination of Lamotrigine, Topiramate, Oxcarbazepine, and 10,11-dihydro-10-hydroxycarbazepine in Human Blood Plasma by UHPLC-MS/MS

Background:

Lamotrigine (LTG), topiramate (TPM), and oxcarbazepine (OXC) are commonly used antiepileptic drugs. The bioactivity and toxicity of these drugs were related to their blood concentrations which varied greatly among individuals and required to be monitored for dose adjustment. However, the commercial method for monitoring of these drugs is not available in China.

Methods:

A UHPLC-MS/MS method for simultaneous determination of LTG, TPM, OXC, and OXC active metabolite (10,11-dihydro-10-hydroxycarbazepine, MHD) was developed and validated according to the guidelines and applied in clinical practice.

Results:

he separation was achieved by using methanol and water (both contain 0.1% formic acid) at 0.4 mL/min under gradient elution within 3 min. For all analytes, the isotope internal standard was used; the selectivity was good without significant carry over; LTG and TPM were linear between 0.06 to 12 mg/L while OXC and MHD were linear between 0.03 to 6 mg/L, the upper limit could be 10-fold higher because 10-fold dilution with water did not affect the results; the intra-day and interday bias and imprecision were -13.11% to 5.42% and < 13.32%; the internal standard normalized recovery and matrix factor were 90.95% to 111.94% and 95.57% to 109.91%; and all analytes were stable under tested conditions. LTG and OXC-D4 shared two ion pairs m/z 257.1 > 212.0 and 257.1 > 184.0, and m/z 257.1 > 240.0 was suggested for OXC-D4 quantitation. Lamotrigine and lamotrigine- 13C3 shared three ion pairs m/z 259.0 > 214.0, 259.0 > 168.0 and 259.0 > 159.0, and m/z 259.0 > 144.9 was suggested for LTG-13C3 quantitation. CBZ had a slight influence on OXC analysis only at 0.225 mg/L (bias, 20.24%) but did not affect MHD analysis. Optimization of chromatography conditions was useful to avoid the influence of isobaric mass transitions on analysis. This method has been successfully applied in 208 patients with epilepsy for dose adjustment.

Conclusions:

An accurate, robust, rapid, and simple method for simultaneous determination of LTG, TPM, OXC, and MHD by UHPLC-MS/MS was developed, validated, and successfully applied in patients with epilepsy for dose adjustment. The experiences during method development, validation, and application might be helpful for other researchers.

Accurate and simple determination of oxcarbazepine in human plasma and urine samples using switchable-hydrophilicity solvent in GC-MS

This work presents a sensitive and rapid analytical method for the determination of oxcarbazepine in human plasma and urine samples. A vortex-assisted switchable hydrophilicity solvent-based liquid phase microextraction (VA-SHS-LPME) was used to preconcentrate oxcarbazepine from the samples before the determination by gas chromatography mass spectrometry. The switchable hydrophilicity solvent was synthesized by protonating N,N-dimethylbenzylamine with carbon dioxide to make it totally miscible with an equivalent volume of water. Parameters of the VA-SHS-LPME method including volume of switchable hydrophilicity solvent, concentration/volume of sodium hydroxide and vortex period were systematically optimized. Under the optimum conditions, good linearity ranging from 27.03 to 353.47 μg/kg was obtained for the analyte. Limit of detection and quantitation values were found to be 6.2 and 21 μg/kg (mass base), respectively. The relative standard deviation was calculated as 6.9% for six replicate measurements of the lowest concentration of the calibration plot. Satisfactory recovery results were calculated in the range of 97-100% for human plasma and urine samples spiked at five different concentrations.

Method validation studies and an inter-laboratory cross validation study of lenvatinib assay in human plasma using LC-MS/MS

Cross validation studies for bioanalytical methods are important to ensure that assay data from all study sites where sample analysis is performed can be compared throughout clinical trials. To support global clinical studies of lenvatinib, a novel multi-targeted tyrosine kinase inhibitor, seven bioanalytical methods by liquid chromatography with tandem mass spectrometry (LC-MS/MS) were developed at five laboratories. In this study, methods were initially validated at each laboratory according to bioanalytical guidelines. For subsequent inter-laboratory cross validation, quality control (QC) samples and clinical study samples with blinded lenvatinib concentrations were assayed to confirm comparable assay data. Lenvatinib and an internal standard were extracted by protein precipitation, liquid-liquid extraction, or solid phase extraction and then detected in positive ion electrospray mode by multiple reaction monitoring using LC-MS/MS. The assay method developed at each laboratory was successfully validated with parameters within the acceptance criteria recommended by the guidelines. In the cross validation study, accuracy of QC samples was within± 15.3% and percentage bias for clinical study samples was within± 11.6%. These findings suggest that lenvatinib concentrations in human plasma can be compared across laboratories and clinical studies.

Population pharmacokinetics of oxcarbazepine and its metabolite 10-hydroxycarbazepine in healthy subjects

Oxcarbazepine is indicated for the treatment of partial or generalised tonic-clonic seizures. Most of the absorbed oxcarbazepine is converted into its active metabolite, 10-hydroxycarbazepine (MHD), which can exist as R-(-)- and S-(+)-MHD enantiomers. Here we describe the influence of the P-glycoprotein (P-gp) inhibitor verapamil, on the disposition of oxcarbazepine and MHD enantiomers, both of which are P-gp substrates. Healthy subjects (n=12) were randomised to oxcarbazepine or oxcarbazepine combined with verapamil at doses of 300mg b.i.d. and 80mg t.i.d., respectively. Blood samples (n=185) were collected over a period of 12h post oxcarbazepine dose. An integrated PK model was developed using nonlinear mixed effects modelling using a meta-analytical approach. The pharmacokinetics of oxcarbazepine was described by a two-compartment model with absorption transit compartments and first-order elimination. The concentration-time profiles of both MHD enantiomers were characterised by a one-compartment distribution model. Clearance estimates (95% CI) were 84.9L/h (69.5-100.3) for oxcarbazepine and 2.0L/h (1.9-2.1) for both MHD enantiomers. The volume of distribution was much larger for oxcarbazepine (131L (97-165)) as compared to R-(-)- and S-(+)-MHD (23.6L (14.4-32.8) vs. 31.7L (22.5-40.9), respectively). Co-administration of verapamil resulted in a modest increase of the apparent bioavailability of oxcarbazepine by 12% (10-28), but did not affect parent or metabolite clearances. Despite the evidence of comparable systemic levels of OXC and MHD following administration of verapamil, differences in brain exposure to both moieties cannot be excluded after P-glycoprotein inhibition.

Development and validation of a reversed-phase HPLC method for licarbazepine monitoring in serum of patients under oxcarbazepine treatment

Licarbazepine is the pharmacologically active metabolite of oxcarbazepine, a drug indicated for the treatment of partial seizures and bipolar disorders. Several HPLC methods have been developed thus far but there is lack of control for interferences from antipsychotic drugs. The aim of the present study was to develop a simple, low-cost and reliable HPLC-UV method for the determination of licarbazepine in human serum in the presence of co-administered antiepileptic, antipsychotic and commonly prescribed drugs. Sample preparation consisted of a single protein precipitation step with methanol. Separation lasted ~9 min on a reversed-phase C₁₈ column using a mobile phase composed of 50 mm sodium-dihydrogen-phosphate-monohydrate/acetonitrile (70:30, v/v) delivered isocratically at 0.9 mL/min and 30°C. Wavelength was 210 nm and calibration curve was linear with r² 0.998 over the range 0.2-50.0 μg/mL. Coefficient of variation was <5.03% and bias <-4.92%. Recovery ranged from 99.49 to 104.52% and the limit of detection was 0.0182 μg/mL. No interferences from the matrix or from antiepileptic, antipsychotic and commonly prescribed drugs were observed. The method was applied to serum samples of patients under oxcarbazepine treatment and proved to be a useful tool for the therapeutic drug monitoring of licarbazepine during monotherapy or adjunctive treatment of seizures or affective disorders.

Bioanalytical method for evaluating the pharmacokinetics of the GCP-II inhibitor 2-phosphonomethyl pentanedioic acid (2-PMPA)

2-Phosphonomethyl pentanedioic acid (2-PMPA) is a potent and selective inhibitor of glutamate carboxypeptidase-II, an enzyme which catabolizes the abundant neuropeptide N-acetyl-aspartyl-glutamate (NAAG) to N-acetylaspartate (NAA) and glutamate. 2-PMPA demonstrates robust efficacy in numerous animal models of neurological disease, however its pharmacokinetics has not yet been fully described. 2-PMPA is a highly polar compound with multiple negative charges causing significant challenges for analysis in biological matrices. Here we report a derivatization method for the acidic groups that involved protein precipitation with acetonitrile followed by reaction with N-tert-butyldimethysilyl-N-methyltrifluoroacetamide (MTBSTFA). The silylated analyte with transitions (683→551.4) and the internal standard (669→537.2) were monitored by tandem mass spectrometry with electrospray positive ionization mode. The method was subsequently used to evaluate 2-PMPA pharmacokinetics in rats. Intraperitoneal administration of 100mg/kg 2-PMPA resulted in maximum concentration in plasma of 275μg/mL at 0.25h. The half-life, area under the curve, apparent clearance, and volume of distribution were 0.64h, 210μg×h/mL, 7.93mL/min/kg, and 0.44L/kg, respectively. The tissue/plasma ratios in brain, sciatic nerve and dorsal root ganglion were 0.018, 0.120 and 0.142, respectively. In summary, a sensitive analytical method for 2-PMPA is reported that can be employed for similarly charged molecules.

An improved simple LC-MS/MS method for the measurement of serum aripiprazole and its major metabolite

BACKGROUND AND OBJECTIVES

Current liquid chromatographic tandem mass spectrometry (LC-MS/MS) methods to measure serum levels of aripiprazole (Ar) and dehydroaripiprazole (DHAr) are sensitive, but difficult to use in a hospital context. We aimed to develop a rapid LC-MS/MS method allowing reliable level measurement in the presence of co-administered drugs, withdrawing samples from 22 patients with acute agitation receiving 9.75 mg aripiprazole IM injection.

METHOD

We developed a sensitive and selective HPLC-MS/MS method to measure serum Ar and DHAr levels in a hospital laboratory, requiring minimal sample preparation and inferior sample volume compared to previous LC-MS/MS methods. Analytes were separated on a reversed-phase HPLC (run-time, 10 min). A triple quadrupole tandem mass spectrometer was used for quantitative analysis in positive mode by a multiple reaction monitoring. Samples were drawn 2, 4, 6, and 24h post-injection.

RESULTS

Calibration curves (2-1000 ng/mL for Ar and 3.5-500 ng/mL for DHAr) were linear, with mean correlation coefficient >0.9998. Within- and between-day precision and accuracy were within 10%. Mean recovery was 95.2 ± 4.5% for Ar and 97.6 ± 7.2% for DHAr. Ar and DHAr peaks were not affected by other co-administered psychotropic drugs.

CONCLUSION

Our method measured Ar and DHAr concentrations reliably, simply and rapidly without employing many reagents, as currently existing methods.

Analysis of selected anticonvulsants by high performance liquid chromatography-tandem mass spectrometry

A method for the analysis of the basic antiepileptic compounds felbamate, lamotrigine, carbamazepine, carbamazepine-10,11-epoxide, gabapentin, pregabalin, levetiracetam, and oxcarbazepine monohydroxy derivative (oxcarb MHD) in human plasma is described. This protocol incorporates a simplified sample preparation step followed by quantitative high performance chromatography-tandem mass spectrometry detection of commonly prescribed and monitored anticonvulsant drugs. Since polytherapy is common in epilepsy patients, use of a multiconstituent assay can improve laboratory efficiency and reduce required analytical time.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Cross validation and ruggedness testing of analytical methods used for the quantification of urinary phthalate metabolites

Since the publication of our first analytical method in 2000 to detect and quantify phthalate metabolites in human urine, we have modified the method several times to improve performance, reduce the volume of matrix and solvents used, and to increase the number of analytes in one analytical run. We performed cross method validation and ruggedness testing after each modification to ensure that the analytical method adopted is robust and produces accurate and reproducible data when compared to the previously used method. Here, we present the results from the evaluation of the ruggedness of our analytical approach under variable experimental conditions, using the current analytical method. Minor deviations of the standard experimental conditions, i.e., pH, incubation time, amount of deconjugation enzyme, and incubation temperature, had no effect on final analyte concentrations. Furthermore, we validated the method to ensure accuracy at concentrations beyond the highest calibration standard. The concentrations obtained by using a lower volume of urine agreed well with original levels, suggesting broad linear calibration range as well as complete hydrolysis of the glucuronide conjugates with the standard amount of beta-glucuronidase used for deglucuronidation; also, the time of incubation (90 min) was adequate regardless of the amount of glucuronide present. We also summarize the precision of concentration data acquired by the five different analytical approaches we have used since 2000. The correlation plots of concentration data for each analyte obtained from split sample analysis, using three of these approaches, produced linear curves (R(2)>0.98) with slopes and intercepts that were not statistically different (p>0.05) from 1 and 0, respectively. These results suggest that the data are reproducible and accurate, regardless of the analytical method used. Furthermore, analysis of quality control urine samples made over the years confirmed the stability of the phthalate metabolites in urine at -70 degrees C for several years and the consistency of the analytical measurements obtained by using various methodological approaches over time.