A chiral HPLC-UV method for the quantification of dibenz[b,f]azepine-5-carboxamide derivatives in mouse plasma and brain tissue: eslicarbazepine acetate, carbamazepine and main metabolites

For the first time, a selective and sensitive chiral HPLC-UV method was developed and fully validated for the simultaneous quantification of eslicarbazepine acetate (ESL), carbamazepine (CBZ), S-licarbazepine (S-Lic), R-licarbazepine (R-Lic), oxcarbazepine (OXC) and carbamazepine-10,11-epoxide (CBZ-E), in mouse plasma and brain homogenate supernatant. After the addition of chloramphenicol as the internal standard, samples were processed using an SPE procedure. The chiral chromatographic analysis was carried out on a LiChroCART 250-4 ChiraDex column, employing a mobile phase of water and methanol (88:12, v/v) pumped at 0.9 mL/min and the UV detector set at 235 nm. The assay was linear (r(2) ≥0.995) for ESL, CBZ, OXC, S-Lic, R-Lic and CBZ-E in the range of, respectively, 0.2-4, 0.4-30, 0.1-60, 0.2-60, 0.2-60 and 0.2-30 μg/mL, in plasma, and of 0.06-1.5 μg/mL for ESL, 0.12-15 μg/mL for CBZ and CBZ-E and 0.06-15 μg/mL for OXC and both licarbazepine (Lic) enantiomers in brain homogenate supernatant. The overall precision was within 8.71% and accuracy ranged from -7.55 to 8.97%. The recoveries of all the compounds were over 92.1%. Afterwards, the application of the method was demonstrated using real plasma and brain samples obtained from mice administered simultaneously with ESL and CBZ.     

Analysis of carbamazepine and its active metabolite, carbamazepine-10,11-epoxide, in human plasma using high-performance liquid chromatography

A sensitive method based on high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection was developed for the determination of carbamazepine (CBZ) and one of its active metabolites, carbamazepine-10,11-epoxide (CBZ-E) in human plasma. CBZ, CBZ-E and the internal standard (IS) 10,11-dihydrocarbamazepine were extracted from human plasma into methyl tert-butyl ether. CBZ, CBZ-E and the IS were successfully separated on an RP C18 column with a mobile phase of acetonitrile:methanol:water (18:19:63, v/v/v) and monitored via UV detection at 210 nm. The calibration curves were linear over the concentration ranges of 0.01–10 μg/mL for CBZ and 0.005–5 μg/mL for CBZ-E in human plasma, respectively. The method displayed excellent sensitivity, precision and accuracy, and was successfully applied to the quantification of CBZ and CBZ-E in human plasma after oral administration of a single 200 mg CBZ CR tablet. This method is suitable for bioequivalence studies following single doses given to healthy volunteers.     

Isocratic Reversed-Phase HPLC for Simultaneous Separation and Determination of Seven Antiepileptic Drugs and Two of their Active Metabolites in Human Plasma

A simple reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of the antiepileptic drugs (AEDs) zonisamide (ZNS), primidone (PRI), lamotrigine (LTG), phenobarbital (PB), phenytoin (PHT), oxcarbazepine (OXC), and carbamazepine (CBZ) and two of their active metabolites, monohydroxycarbamazepine (MHD) and carbamazepine 10,11-epoxide (CBZE) in human plasma. Plasma (100 μL) was pretreated by deproteinization with 300 μL methanol containing 20 μg mL⁻¹ propranolol hydrochloride as internal standard. HPLC was performed on a C₈ column (4.6 mm × 250 mm; particle size 5 μm) with methanol–acetonitrile–0.1% trifluoroacetic acid, 235:120:645 (v/v), as mobile phase at a flow rate of 1.5 mL min⁻¹. ZNS, OXC, and CBZ were monitored by UV detection at 235 nm, and PRI, LTG, MHD, PB, PHT, and CBZE by UV detection at 215 nm. Relationships between response and concentration were linear over the concentration ranges 1–80 μg mL⁻¹ for ZNS, 5–50 μg mL⁻¹ for PRI, 1–25 μg mL⁻¹ for LTG, 1–50 μg mL⁻¹ for MHD, 5–100 μg mL⁻¹ for PB, 1–10 μg mL⁻¹ for CBZE, 0.5–25 μg mL⁻¹ for OXC, 1–50 μg mL⁻¹ for PHT, and 1–25 μg mL⁻¹ for CBZ. Intra-day and inter-day reproducibility were adequate (coefficients of variation were ≤11.6%) and absolute recovery ranged from 95.2 ± 6.13 to 107.7 ± 7.76% for all the analytes; for the IS recovery was 98.69 ± 1.12%. The method was proved to be accurate, reproducible, convenient, and suitable for therapeutic monitoring of the nine analytes.     

Routine monitoring of carbamazepine and carbamazepine-10,11-epoxide in plasma by high-performance liquid chromatography using 10-methoxycarbamazepine as internal standard

Carbamazepine and carbamazepine-10,11-epoxide were separated by high-performance liquid chromatography (HPLC) with acetonitrile-water as mobile phase, and detection was effected by UV absorption at 215 nm with a total retention time of less than 10 min. Plasma samples were extracted with dichloromethane and 4 M sodium hydroxide, and 10-methoxy-carbamazepine was added as internal standard. Other commonly used anticonvulsant drugs present in plasma showed no significant interference. The within-batch coefficient of variation for carbamazepine was 4.9% and carbamazepine-10,11-epoxide 5.9%. Between-batch coefficients of variation were 3.7% and 5.3%, respectively. Mean recovery for carbamazepine was 100.2% and for carbamazepine-10,11-epoxide 100.6%. This HPLC method was compared with both an enzyme immunoassay procedure (EMIT) and a gas-liquid chromatographic (GLC) method. Correlation coefficient between HPLC/EMIT for carbamazepine was 0.983, HPLC/GLC carbamazepine 0.988 and HPLC/GLC carbamazepine-10,11-epoxide 0.981.     

A chiral liquid chromatography method for the simultaneous determination of oxcarbazepine, eslicarbazepine, R-licarbazepine and other new chemical derivatives BIA 2-024, BIA 2-059 and BIA 2-265, in mouse plasma and brain

Recently, in silico models have been developed to predict drug pharmacokinetics. However, before application, they must be validated and, for that, information about structurally similar reference compounds is required. A chiral liquid chromatography method with ultraviolet detection (LC‐UV) was developed and validated for the simultaneous quantification of BIA 2–024, BIA 2–059, BIA 2–265, oxcarbazepine, eslicarbazepine (S‐licarbazepine) and R‐licarbazepine in mouse plasma and brain. Compounds were extracted by a selective solid‐phase extraction procedure and their chromatographic separation was achieved on a LiChroCART 250–4 ChiraDex column using a mobile phase of water–methanol (92:8, v/v) pumped at 0.7 mL/min. The UV detector was set at 235 nm. Calibration curves were linear (r² ≥ 0.996) over the concentration ranges of 0.2–30 µg/mL for oxcarbazepine, eslicarbazepine and R‐licarbazepine; 0.2–60 µg/mL for the remaining compounds in plasma; and 0.06–15 µg/mL for all the analytes in brain homogenate. Taking into account all analytes at these concentration ranges in both matrices, the overall precision did not exceed 9.09%, and the accuracy was within ±14.3%. This LC‐UV method is suitable for carrying out pharmacokinetic studies with these compounds in mouse in order to obtain a better picture of their metabolic pathways and biodistribution. Copyright © 2011 John Wiley & Sons, Ltd.     

Simultaneous HPLC Determination of Oxcarbazepine,Carbamazepine and Their Metabolites in Serum

Abstract

We propose a simple procedure for the simultaneous determination of the anticonvulsants oxcarbazepine, carbamazepine and three of their metabolites (10-hydroxy-10, 11-dihydro-carbamazepine, trans-10, 11-dihydroxy-10, 11-dihydro-carbamazepine and 10, 11-epoxy-carbamazepine) in serum or plasma. The alkalinized sample is extracted with ethyl acetate. The extract is evaporated to dryness and taken up with the mobile phase. An aliquot is injected into the liquid chromatograph and eluted with water/methanol/acetonitrile (55/40/5, by vol.) on a 5-μm C-18 reversed-phase column. Eluent is monitored at 254 nm. No interference by other anticonvulsants or by endogenous constituents from the sample is observed. Owing to its good precision, specificity, sensitivity, and selectivity, this method is well adapted to the therapeutic monitoring of oxcarbazepine or carbamazepine treated patients, as well as for pharmacokinetic studies.     

Enantioselective HPLC-UV method for determination of eslicarbazepine acetate (BIA 2-093) and its metabolites in human plasma

Eslicarbazepine acetate (BIA 2-093) is a novel central nervous system drug undergoing clinical phase III trials for epilepsy and phase II trials for bipolar disorder. A simple and reliable chiral reversed-phase HPLC-UV method was developed and validated for the simultaneous determination of eslicarbazepine acetate, oxcarbazepine, S-licarbazepine and R-licarbazepine in human plasma. The analytes and internal standard were extracted from plasma by a solid-phase extraction using Waters Oasis HLB cartridges. Chromatographic separation was achieved by isocratic elution with water-methanol (88:12, v/v), at a flow rate of 0.7 mL/min, on a LichroCART 250-4 ChiraDex (beta-cyclodextrin, 5 microm) column at 30 degrees C. All compounds were detected at 225 nm. Calibration curves were linear over the range 0.4-8 microg/mL for eslicarbazepine acetate and oxcarbazepine, and 0.4-80 microg/mL for each licarbazepine enantiomer. The overall intra- and interday precision and accuracy did not exceed 15%. Mean relative recoveries varied from 94.00 to 102.23% and the limit of quantification of the assay was 0.4 microg/mL for all compounds. This method seems to be a useful tool for clinical research and therapeutic drug monitoring of eslicarbazepine acetate and its metabolites S-licarbazepine, R-licarbazepine and oxcarbazepine.     

Simultaneous quantitation of salivary carbamazepine, carbamazepine-10,11-epoxide, phenytoin and phenobarbitone by high-performance liquid chromatography

A rapid, sensitive and accurate high-performance liquid chromatographic method for the simultaneous quantitation of phenobarbitone, phenytoin, carbamazepine and carbamazepine-10,11-epoxide in saliva is described. Only small volumes of saliva (100 microliters) are required. Separation of the drugs is achieved by reversed-phase chromatography on a Nova-Pak C18 column, with a mobile phase of acetonitrile-phosphate buffer at a flow-rate of 2.0 ml/min. Detection is effected by ultra-violet absorption at 215 nm. The total run time is under 12.5 min per assay. A precipitation but no extraction step is involved, simplifying the assay method. Salivary concentrations in the range 0.25-25 micrograms/ml for carbamazepine, 0.5-20 micrograms/ml for phenytoin and phenobarbitone and 0.4-20 micrograms/ml for carbamazepine-10,11-epoxide can be measured. Recovery varies from 94 to 108%. The method has been used for routine measurements of anticonvulsants in saliva collected daily from patients with intractable epilepsy.     

Simultaneous Determination of Carbamazepine and its Active Metabolite Carbamazepine-10,11-epoxide in Human Plasma by UPLC

A simple method for the determination of carbamazepine and its active metabolite carbamazepine-10,11-epoxide by ultra performance liquid chromatography (UPLC) with ultraviolet absorbance detection (TUV) was developed. The method involves a two-step protein precipitation by liquid–liquid extraction. Phenytoin sodium was used as the internal standard. The separation was carried out on Acquity C18 column with acetonitrile:methanol:KH₂PO₄ buffer (adjusting pH to 4.6 with 85% o-phosphoric acid) (180/180/170, v/v/v) as the mobile phase at a flow rate of 0.4 mL min⁻¹. Linear detection response was obtained for concentrations ranging from 50 to 5,000 ng mL⁻¹. The limit of quantification (LOQ) was 50 ng mL⁻¹. The method was validated successfully for the determination of carbamazepine and its active metabolite carbamazepine-10,11-epoxide, which can be applied through pharmacokinetics and bioequivalence studies.

     

Simultaneous Ion-Pairing Liquid Chromatographic Determination of the Major Metabolites of Styrene and Carbamazepine,and of Unchanged Carbamazepine in Urine

Abstract

A high-performance liquid chromatographic method for a simultaneous quantitative determination of carbamazepine (CBZ) and of the major metabolites of CBZ (trans-10,11-dihydroxy-10,11-dihydrocarbamazepine, TDC; carbamazepine-10,11-epoxide, CBZ-E) and those of styrene (S) (hippuric acid, HA; mandelic acid, MA; phenylglyoxylic acid, PA) in the rat urine is described. Separation is achieved on a Nova-Pak reverse-phase column by isocratic elution. Excellent resolution was obtained by adding to the acetonitrile-water mobile phase, tetrabutylammonium chloride (0.005 M) and methanol (1%). Detection is effected by UV absorption at 230 nm with a total analysis time of less than 18 min. An aliquot of diluted urine is injected directly onto the liquid chromatographic column. The limits of sensitivity of CBZ, CBZ-E, TDC, HA, MA, and PA are 3.3, 2.0, 1.8, 3.1, 1.2, and 3.1 μg/ml of diluted rat urine, respectively. Precision and accuracy of the method are found to be acceptable. The method can be used for studying the interaction between these two xenobiotics. Preliminary studies have shown its potential application to human investigations.     

Octakis-6-sulfato-gamma-cyclodextrin as additive for capillary electrokinetic chromatography of dibenzoazepines: carbamazepine,oxcarbamazepine and their metabolites

Single isomer octakis-(2,3-dihydroxy-)6-sulfato-gamma-cyclodextrin used as pseudostationary phase of the background electrolyte interacts with dibenzo[b,f]azepines (consisting of a condensed 3-ring system) and forms negatively charged complexes. Hydroxygroups in position 2 and 3 at carbamazepine increase the extent of interaction, whereas substitution by oxygen at position 10 and/or 11 reduces it. The complex constants for the analytes are ranging from few tens L/mol (10-hydroxycarbamazepine, 10,11-dihydroxycarbamazepine, 10,11-epoxycarbamazepine, oxcarbazepine) to several hundreds L/mol (carbamazepine, 2-hydroxycarbamazepine, 3-hydroxycarbamazepine), and are much larger than those of the analytes with octakis-(2,3-dimethyl-)-6-sulfato-gamma-cyclodextrin. Full enantiomeric separation of the chiral metabolites of carbamazepine and oxcarbazepine is obtained at octakis-(2,3-dihydroxy-)-6-sulfato-gamma-cyclodextrin concentrations of about 10 mM (3 mM borate buffer, pH 8.5). Compared to heptakis-6-sulfato-beta-cyclodextrin, selectivity differs and stereoselectivity is more pronounced.     

Quantitative determination of Phakellistatin 13, a new cyclic heptapeptide,in rat plasma by liquid chromatography/tandem mass spectrometry: application to a pharmacokinetic study

A sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, followed by a 96-well protein precipitation, has been developed and fully validated for the determination of Phakellistatin 13 (PK13), a new cyclic heptapeptide isolated from the sponge Phakellia fusca Thiele, in rat plasma. After protein precipitation of the plasma samples (50 μL) in a 96-well plate by methanol (200 μL) containing the internal standard Pseudostellarin B (20 ng/mL), the plate was vortex mixed for 3 min. Following filtration for 5 min, the filtrate was directly injected into the LC-MS/MS system. The analytes were separated on an XB-C18 analytical column (5 μm, 50 mm × 4.6 mm i.d.) using an eluent of methanol–water (85:15, v/v) and detected by electrospray ionization mass spectrometry in the negative multiple reaction monitoring mode with a chromatographic run time of 5.0 min. The method was sensitive with a lower limit of quantification (LLOQ) of 0.1 ng/mL, with good linearity (r > 0.999) over the quantitation range of 0.1–5 ng/mL. The validation results demonstrated that this method was significantly specific, accurate, precise, and was successfully applied in measuring levels of PK13 in rat plasma following intravenous administration of 20, 50, and 100 μg/kg of peptide in rats, respectively, which was suitable for the preclinical pharmacokinetic studies on PK13.     

Monolithic spin column extraction and GC-MS for the simultaneous assay of diquat,paraquat, and fenitrothion in human serum and urine

We present a method based on monolitic spin column extraction and gas chromatography–mass spectrometry as an analytical method for screening diquat (DQ), paraquat (PQ), and fenitrothion in serum and urine. This method is useful for clinical and forensic toxicological analyses. Recovery of DQ, PQ, and fenitrothion from serum and urine, spiked at concentrations between 0.1, 2.5, 20, and 45 μg/ml, ranged from 51.3% to 106.1%. Relative standard deviation percentages were between 3.3% and 14.8%. Detection and quantitation limits for serum and urine were 0.025 and 0.05 μg/ml, respectively, for DQ, 0.1 and 0.1 μg/ml, respectively, for PQ, and 0.025 and 0.05 μg/ml, respectively, for fenitrothion. Therefore, these compounds can be detected and quantified in the case of acute poisoning.     

Separation and quantitation of oxprenolol in urine and pharmaceutical formulations by HPLC using a Chiralpak IC and UV detection

Abstract  

A stereoselective HPLC method has been developed for the simultaneous determination of oxprenolol enantiomers in urine and pharmaceutical products. Enantiomeric resolution of oxprenolol was achieved on cellulose tris(3,5-dichlorophenylcarbamate) immobilized onto a 5 μm spherical porous silica chiral stationary phase (CSP) known as Chiralpak IC with UV detection at 273 nm. The mobile phase consisted of n-hexane:isopropanol:triethylamine 70:30:0.1 (v/v/v) at a flow rate of 1.0 cm³/min. The method was validated for its linearity, accuracy, precision, and robustness. The calibration curves were linear over the range of 0.5–75 μg/cm³, with a detection limit of 0.1 μg/cm³ for each enantiomer. An average recovery of 99.0% and a mean relative standard deviation of 2.6% at 40.0 μg/cm³ for S-(−)- and R-(+)-enantiomers were obtained. The overall recoveries of oxprenolol enantiomers from pharmaceutical formulations were in the range 97.5–99.0%, with RSDs ranging from 0.6 to 0.8%. The mean extraction efficiency of oxprenolol from urine was in the range of 86.0–93.0% at 0.5–5 μg/cm³ for each enantiomer. The assay method proved to be suitable as a chiral quality control for oxprenolol formulations using HPLC and for therapeutic drug monitoring.     

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 r ² 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.     

Determination of isoascorbic acid in fish tissue by hydrophilic interaction liquid chromatography–ultraviolet detection

A new hydrophilic interaction liquid chromatographic (HILIC) method for the simultaneous determination of isoascorbic (IAA) and ascorbic acid (AA) was developed. The separation of IAA and AA was studied in various HILIC stationary phases and the influence of the composition of the mobile phase, the ionic strength and the column temperature to the chromatographic characteristics is presented. The final method used an aminopropyl column under isocratic elution with acetonitrile–100 mM ammonium acetate solution (90:10, v/v) at a flow rate of 0.4 mL/min and a detection wavelength of 240 nm. This method was validated and the calibration curves were found to be linear in the range of 1.0–65 μg/mL for both IAA and AA. The method limit of detection for IAA determination in fish tissue was 2.3 μg/g. Inter-day precision (as %RSD_R) was ranged between 0.56% and 8.3% at three concentration levels, whereas the respected recoveries ranged between 82% and 98%. This method was applied to the determination of IAA (as additive E315) in frozen redfish samples. The hyphenation of the HILIC separation with a tandem mass spectrometer was also studied and the problems encountered with negative electrospray ionization under HILIC separation conditions are discussed.     

Monitoring carbamazepine in surface and wastewaters by an immunoassay based on a monoclonal antibody

The pharmaceutical compound carbamazepine (CBZ) is an emerging pollutant in the aquatic environment and may potentially be used as a wastewater marker. In this work, an enzyme-linked immunosorbent assay (ELISA) for the detection of carbamazepine in surface and sewage waters has been developed. The heterogeneous immunoassay is based on a commercially available monoclonal antibody and a novel enzyme conjugate (tracer) that links the hapten via a hydrophilic peptide (triglycine) spacer to horseradish peroxidase. The assay achieves a limit of detection of 24 ng/L and a quantitation range of 0.05–50 μg/L. The analytical performance and figure of merits were compared to liquid chromatography–tandem mass spectrometry after solid-phase extraction. For nine Berlin surface water samples and one wastewater sample, a close correlation of results was observed. A constant overestimation relative to the CBZ concentration of approximately 30% by ELISA is probably caused by the presence of 10,11-epoxy-CBZ and 2-hydroxy-CBZ in the samples. The ELISA displayed cross-reactivities for these compounds of 83% and 14%, respectively. In a first screening of 27 surface water samples, CBZ was detected in every sample with concentrations between 0.05 and 3.2 μg/L. Since no sample cleanup is required, the assay allowed for the determination of carbamazepine with high sensitivity at low costs and with much higher throughput than with conventional methods.      

Use of spermine and thiabendazole as analyte protectants to improve direct analysis of 16 carbamates by gas chromatography–mass spectrometry in green vegetable matrices

The carbamates are a well-known thermosensible pesticides class, which are highly prone to degradation via fragmentation and/or rearrangement mechanisms leading to a difficult direct gas chromatography (GC) analysis, i.e., without derivatization. In this paper, spermine and thiabendazole both at 1 mg/mL were highlighted as efficient analyte protectants to improve the direct and simultaneous analysis of 16 carbamates both in solvent and green vegetable matrices. These two molecules were compared in mixture or in combination with three well-known efficient analyte protectants 3-ethoxy-1,2-propanediol, d-sorbitol, and l-gulonic acid-γ-lactone. The potential benefits were investigated in GC hyphenated to mass spectrometry (GC–MS) with two injection modes: programmable temperature vaporizing injector in a solvent split mode (PTV-SSI) and on-column injection (OCI). It was shown that the combined effect of the five protective agents led to the best sensitivity improvement with limits of detection between 0.1–0.4 and 0.03–0.1 μg/kg and limits of quantification between 0.3–1.1 and 0.1–0.5 μg/kg for PTV-SSI and OCI mode, respectively. The correlation coefficients from the analyzed 1–500 μg/kg range were all >0.999 both in the solvent and matrices studied. The recoveries of carbamates from three spiked matrices over five replicates at 20 and 100 μg/kg were in the range 90–107% with relative standard deviation (RSD) equal to 2–7% for PTV-SSI and 92–107% with an RSD equal to 1–6% for OCI. The use of spermine and thiabendazole with other analyte protectants shows very efficient partial or total reduction of breakdown of the most sensitive carbamates such as the N-sulfenylated ones. An erratum to this article can be found at     

Simultaneous RP-LC Determination of Losartan Potassium, Ramipril, and Hydrochlorothiazide in Pharmaceutical Preparations

A simple, rapid, and precise reversed-phase high-performance liquid chromatographic method has been developed for simultaneous determination of losartan potassium, ramipril, and hydrochlorothiazide. The three drugs were separated on a 150 mm × 4.6 mm i.d., 5 μm particle, Cosmosil C₁₈ column. The mobile phase was 0.025 m sodium perchlorate–acetonitrile, 62:38 (v/v), containing 0.1% heptanesulphonic acid, pH adjusted to 2.85 with orthophosphoric acid, at a flow rate of 1.0 mL min⁻¹. UV detection was performed at 215 nm. The method was validated for linearity, accuracy, precision, and limit of quantitation. Linearity, accuracy, and precision were acceptable in the ranges 35–65 μg mL⁻¹ for losartan, 1.75–3.25 μg mL⁻¹ for ramipril, and 8.75–16.25 μg mL⁻¹ for hydrochlorothiazide.     

Simultaneous determination of ten antiepileptic drugs in human plasma by liquid chromatography and tandem mass spectrometry with positive/negative ion‐switching electrospray ionization and its application in therapeutic drug monitoring

A simple, rapid, and high‐throughput liquid chromatography with tandem mass spectrometry method for the simultaneous quantitation of ten antiepileptic drugs in human plasma has been developed and validated. The method required only 10 μL of plasma. After simple protein precipitation using acetonitrile, the analytes and internal standard diphenhydramine were separated on a Zorbax SB‐C₁₈ column (50 × 4.6 mm, 2.7 μm) using acetonitrile/water as the mobile phase at a flow rate of 0.9 mL/min. The total run time was 6 min for each sample. The validation results of specificity, matrix effects, recovery, linearity, precision, and accuracy were satisfactory. The lower limit of quantification was 0.04 μg/mL for carbamazepine, 0.02 μg/mL for lamotrigine, 0.01 μg/mL for oxcarbazepine, 0.4 μg/mL for 10‐hydroxycarbazepine, 0.1 μg/mL for carbamazepine‐10,11‐epoxide, 0.15 μg/mL for levetiracetam, 0.06 μg/mL for phenytoin, 0.3 μg/mL for valproic acid, 0.03 μg/mL for topiramate, and 0.15 μg/mL for phenobarbital. The intraday precision and interday precision were less than 7.6%, with the accuracy ranging between –8.1 and 7.9%. The method was successfully applied to therapeutic drug monitoring of 1237 patients with epilepsy after administration of standard antiepileptic drugs. The method has been proved to meet the high‐throughput requirements in therapeutic drug monitoring.