Determination of Robenacoxib in Plasma Using Reverse-Phase Liquid Chromatography

The aim of this paper was to present a rapid, simple, and straightforward high-performance liquid chromatography (HPLC) method for the determination of robenacoxib in plasma. Robenacoxib is a member of the COXIB group of nonsteroidal anti-inflammatory drugs developed for veterinary use. The method was validated based on the FDA Guidance for Industry: Bioanalytical Method Validation for selectivity, linearity, accuracy, precision, stability, and recovery. Methylene chloride was used in a liquid–liquid extraction that produced an average recovery of 97%. Chromatographic separation occurred on a Sunfire C₁₈ column (4.6 × 150 mm) using an isocratic combination of 0.025% trifluoroacetic acid in water and acetonitrile (50:50, v/v). Ultraviolet absorbance was measured at 275 nm and the flow rate was 1.1 mL/min. The method was linear in the concentration range of 0.1 to 50 µg/mL. The assay variability ranged from 2.2% to 9.2% while the accuracy was 100%. The lower limit of quantification for a 0.1 mL sample size was 0.1 µg/mL. The method was used for the determination of robenacoxib in plasma samples.