Journal of Pharmaceutical and Biomedical Analysis 56 (2011) 771–777 Contents lists available at ScienceDirect Journal of Pharmaceutical and Biomedical Analysis jou rn al h om epage: www.elsevier.com/locate/jpba Simple and accurate quantitative analysis of ten antiepileptic drugs in human plasma by liquid chromatography/tandem mass spectrometry Kwon-Bok Kim a , Kyung-Ah. Seo a , Sung-Eun Kim c , Soo Kyung Bae a,1 , Dong-Hyun Kim a , Jae-Gook Shin a,b,∗ a Department of Pharmacology and PharmacoGenomics Research Center, Inje University College of Medicine, Busan, South Korea b Department of Clinical Pharmacology and Clinical Trial Center, Inje University Busan Paik Hospital, Busan, South Korea c Inje University Busan Paik Hospital, Busan, South Korea a r t i c l e i n f o Article history: Received 12 May 2011 Received in revised form 14 July 2011 Accepted 18 July 2011 Available online 23 July 2011 Keywords: Antiepileptic drugs Liquid chromatography (LC)–tandem mass spectrometry (MS/MS) Human plasma a b s t r a c t A simple, accurate, and sensitive liquid chromatography (LC)–tandem mass spectrometry (MS/MS) method has been developed for the simultaneous quantification of 10 antiepileptic drugs (AEDs; gabapentin (GBP), levetiracetam (LEV), valproic acid (VPA), lamotrigine (LTG), carbamazepine-10,11- epoxide (CBZ-epoxide), zonisamide (ZNS), oxcarbazepine (OXC), topiramate (TPM), carbamazepine (CBZ), phenytoin (PHT)) in human plasma as a tool for drug monitoring. d 10 -Phenytoin (d 10 -PHT) and d 6- valproic acid (d 6 -VPA) were used as internal standards for the positive- and negative-ionization modes, respec- tively. Plasma samples were precipitated by the addition of acetonitrile, and supernatants were analyzed on a C18 reverse-phase column using an isocratic elution. Detection was carried out in selected reac- tion monitoring (SRM) mode. The calibration curves were linear over a 50-fold concentration range, with correlation coefficients (r 2 ) greater than 0.997 for all AEDs. The intra- and inter-day precision was less than 12%, and the accuracy was between 85.9 and 114.5%. This method was successfully used in the identification and quantitation of AEDs in patients undergoing mono- or polytherapy for epilepsy. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Carbamazepine (CBZ), phenytoin (PHT) and valproic acid (VPA) are well-known antiepileptic drugs (AEDs). Since the 1993s, new AEDs, including gabapentin (GBP), lamotrigine (LTG), lev- etiracetam (LEV), oxcarbazepine (OXC), topiramate (TPM), and zonisamide (ZNS), have been approved and introduced to the market [1]. These AEDs have differing mechanisms of action that indirectly affect voltage-dependent calcium channels, sodium channel blockage, and GABAergic inhibition of drug interactions [2]. Patients use monotherapy or polytherapy to control seizures. However, polytherapy often causes undesirable side effects, due to drug–drug interactions among co-administered AEDs. Admin- istration of GBP with CBZ increased plasma concentrations of carbamazepine 10,11-epoxide (CBZ-epoxide), which also possesses ∗ Corresponding author at: Department of Clinical Pharmacology and Clinical Trial Center, Inje University Busan Paik Hospital, 633-165, Gaegum-Dong, Jin-Gu, Busan 614-735, South Korea. Tel.: +82 51 890 8969; fax: +82 51 892 1232. E-mail address: phshinjg@inje.ac.kr (J.-G. Shin). 1 Present address: College of Pharmacy, Catholic University, Bucheon, Kyunggi- do, South Korea. antiepileptic activity [3,4]. Thus, it is necessary to simultane- ously monitor AEDs, including their active metabolites, to develop therapies without side effects. Various analytical tools have been developed for therapeutic drug monitoring of AEDs, including high-performance liquid chromatography (HPLC) coupled with ultraviolet detection [5–9], an evaporative light-scattering detec- tor [10], fluorescence polarization immunoassay [11,12], and an enzyme-multiplied immunoassay technique [13,14]. However, these methods require time-consuming and laborious extraction procedures or relatively large sample volumes (∼1 mL) as well as lengthy chromatographic run times, limiting their through- put capacity and sensitivity. Recently, Subramanian et al. [15] reported a liquid chromatography atmospheric pressure chemical ionization mass spectrometry (LC–APCI-MS) method with solid- phase extraction (SPE) to simultaneously detect six AEDs and three metabolites in human plasma. However, this method can- not be applied to routinely prescribed drugs, such as GBP, LEV, and VPA. In the present study, we established a fully validated, rapid, and accurate LC–MS/MS method for the simultaneous quantification of nine frequently prescribed AEDs in human plasma. CBZ-epoxide, an active metabolite of CBZ, was included in this assay because it is pharmacologically active. Felbamate was not included in this 0731-7085/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpba.2011.07.019