**Pharmacokinetic Evaluation of Metabolic Drug Interactions between Repaglinide and Celecoxib by a Bioanalytical HPLC Method for Their Simultaneous Determination with Fluorescence Detection**

**Dong-Gyun Han 1,**† **, Jinsook Kwak 1,**† **, Seong-Wook Seo <sup>1</sup> , Ji-Min Kim <sup>1</sup> , Jin-Wook Yoo <sup>1</sup> , Yunjin Jung <sup>1</sup> , Yun-Hee Lee <sup>2</sup> , Min-Soo Kim <sup>1</sup> , Young-Suk Jung <sup>1</sup> , Hwayoung Yun 1,\* and In-Soo Yoon 1,\***


Received: 15 May 2019; Accepted: 29 July 2019; Published: 2 August 2019

**Abstract:** Since diabetes mellitus and osteoarthritis are highly prevalent diseases, combinations of antidiabetic agents like repaglinide (REP) and non-steroidal anti-inflammatory drugs (NSAID) like celecoxib (CEL) could be commonly used in clinical practice. In this study, a simple and sensitive bioanalytical HPLC method combined with fluorescence detector (HPLC-FL) was developed and fully validated for simultaneous quantification of REP and CEL. A simple protein precipitation procedure and reversed C18 column with an isocratic mobile phase (mixture of ACN and pH 6.0 phosphate buffer) were employed for sample preparation and chromatographic separation. The fluorescence detector was set at a single excitation/emission wavelength pair of 240 nm/380 nm. The linearity (10–2000 ng/mL), accuracy, precision, extraction recovery, matrix effect, and stability for this method were validated as per the current FDA guidance. The bioanalytical method was applied to study pharmacokinetic interactions between REP and CEL in vivo, successfully showing that concurrent administration with oral REP significantly altered the pharmacokinetics of oral CEL. Furthermore, an in vitro metabolism and protein binding study using human materials highlighted the possibility of metabolism-based interactions between CEL and REP in clinical settings.

**Keywords:** celecoxib; drug–drug interaction; fluorescence; HPLC; metabolism; repaglinide
