Detection and quantification of the selective EP4 receptor antagonist CJ-023423 (grapiprant) in canine plasma by HPLC with spectrofluorimetric detection

Grapiprant, a novel pharmacologically active ingredient, acts as a selective EP4 receptor antagonist whose physiological ligand is prostaglandin E2 (PGE2). It is currently under development for use in humans and dogs for the control of pain and inflammation associated with osteoarthritis. The aim of the present study was to develop an easy and sensitive method to quantify grapiprant in canine plasma and to apply the method in a canine patient. Several parameters, both in the extraction and detection method were evaluated. The final mobile phase consisted of ACN:AcONH (20mM) solution, pH 4 (70:30, v/v) at a flow rate of 1mL/min. The elution of grapiprant and IS (metoclopramide) was carried out in isocratic mode through a Synergi Polar-RP 80A analytical column (150mm×4.6mm). The best excitation and emission wavelengths were 320 and 365nm, respectively. Grapiprant was extracted from the plasma using CHCl, which gave a recovery of 88.1±10.22% and a lower limit of quantification (LLOQ) of 10ng/mL. The method was validated in terms of linearity, limit of detection (LOD), LLOQ, selectivity, accuracy and precision, extraction recovery, stability, and inter-laboratory cross validation, according to international guidelines. The chromatographic runs were specific with no interfering peaks at the retention times of the analyte and IS, as confirmed by HPLC-MS experiments. In conclusion, this was a simple and effective method using HPLC-FL to detect grapiprant in plasma, which may be useful for future pharmacokinetic studies