Development and validation of a highly sensitive LC‐MS/MS method for quantitation of dexlansoprazole in human plasma: application to a human pharmacokinetic study Kishore Kumar Hotha a,b , D. Vijaya Bharathi a * , B. Jagadeesh a , L. K. Ravindranath c , K. N. Jaya Veera b and V. Venkateswarulu a ABSTRACT: A highly sensitive, specific and simple LC‐MS/MS method was developed for the simultaneous estimation of dexlansoprazole (DEX) with 50 μL of human plasma using omeprazole as an internal standard (IS). The API‐4000 LC‐MS/ MS was operated under multiple reaction‐monitoring mode using electrospray ionization. A simple liquid–liquid extraction process was used to extract DEX and IS from human plasma. The total run time was 2.00 min and the elution of DEX and IS occurred at 1.20 min. This was achieved with a mobile phase consisting of 0.2% ammonia–acetonitrile (20:80, v/v) at a flow rate of 0.50 mL/min on an X‐terra RP 18 (50 × 4.6 mm, 5 μm) column. The developed method was validated in human plasma with a lower limit of quantitation of 2 ng/mL for DEX. A linear response function was established for the range of concentrations 2.00–2500.0 ng/mL (r > 0.998) for DEX. The intra‐ and inter‐day precision values for DEX met the acceptance criteria as per FDA guidelines. DEX was stable in the battery of stability studies, viz. bench‐top, auto‐sampler and freeze–thaw cycles. The developed assay method was applied to an oral bioequivalence study in humans. Copyright © 2011 John Wiley & Sons, Ltd. Keywords: DEX; LC‐MS/MS; method validation; human plasma; pharmacokinetics Introduction Dexlansoprazole (DEX; CAS no. 138530‐94‐6; Fig. 1), chemically (R)‐(+) 2‐{[3‐methyl‐4‐(2, 2, 2‐trifluoroethoxy) pyridin‐2‐yl] methylsulfinyl}‐1H‐benzo[d]imidazole, is a proton pump inhib- itor that is marketed under the brand name Dexilant (Kapidex was renamed Dexilant in the USA to avoid name confusion). Chemically, it is an enantiomer of lansoprazole. It is available commercially as delayed release capsules (30 and 60 mg; www. druglib.com/druginfo/kapidex/). DEX is the newest addition to the proton pump inhibitor (PPI) class and is approved for heartburn associated with symptomatic nonerosive gastro- esophageal reflux disease (GERD), the healing of erosive esophagitis (EE) and the maintenance of healed EE. DEX is a PPI that suppresses gastric acid secretion by specific inhibition of (H + ,K + )‐ATPase in the gastric parietal cell. DEX MR is a Dual Delayed Release (DDR) formulation of DEX, with two distinct drug release periods to prolong the plasma DEX concentration– time profile and extend the duration of acid suppression. Clinical studies show that DEX MR produces a dual‐peak pharmacoki- netic profile that maintains therapeutic plasma drug concentra- tions longer than lansoprazole, with a single‐peak pharmacoki- netic profile, and increases the percentage of time that intragastric pH is >4 (Metz et al., 2009a; Sharma et al., 2009). DEX is extensively metabolized in the liver by oxidation, reduction and subsequent formation of sulfate, glucuronide and glutathione conjugates to inactive metabolites. Oxidative metabolites are formed by the cytochrome P450 (CYP) enzyme system, including hydroxylation mainly by CYP2C19, and oxidation to the sulfone by CYP3A4. CYP2C19 is a polymorphic liver enzyme that exhibits three phenotypes in the metabolism of CYP2C19 substrates; extensive metabolizers (*1/*1), intermediate metabolizers (*1/mutant) and poor metabolizers (mutant/mutant). DEX is the major circulating component in plasma regardless of CYP2C19 metabolizer status. In CYP2C19 intermediate and extensive metabolizers, the major plasma metabolites are 5‐hydroxy DEX and its glucuronide conjugate, while in CYP2C19 poor metabolizers DEX sulfone is the major plasma metabolite. In food‐effect studies in healthy subjects receiving DEX under various fed conditions compared with fasting, increases in C max ranged from 12 to 55%, increases in AUC ranged from 9 to 37%, and t max varied (ranging from a * Correspondence to: D. Vijaya Bharathi, Bioanalytical Department, Inte- grated Product Development, Dr Reddy’ s Laboratories Ltd, Bachupalli, Hyderabad‐500 072, India. E-mail: vijayabd@drreddys.com a Bioanalytical Department, Integrated Product Development, Dr Reddy’ s Laboratories Ltd, Bachupalli, Hyderabad‐500 072, India b JNT University, Anantapur‐515 001, A.P, India c Department of Chemistry, S.K. University, Anantapur‐515 001, A.P, India Abbreviations used: CYP, cytochrome P450; DEX, dexlansoprazole; ER, erosive esophagitis; GERD, gastroesophageal reflux disease; PPI, proton pump inhibitor. Biomed. Chromatogr. 2011 Copyright © 2011 John Wiley & Sons, Ltd. Research Article Received 28 January 2011, Accepted 4 April 2011 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/bmc.1645