Determination of febuxostat in human plasma by high performance liquid chromatography (HPLC) with fluorescence-detection

Febuxostat prevents gout attacks by lowering serum urate. Aspects of the pharmacokinetic-pharmacodynamic relationship of febuxostat concentrations to urate in gout patients need further elucidation. In order to undertake these studies, the assay methodology for febuxostat has been enhanced and validated to meet FDA standards. An HPLC method with fluorescence-detection has been modified to increase sensitivity, reduce complexity, shorten the sample preparation process and improve the inter-day coefficient of variation of the lowest quality control sample (0.03 μg/L). Protein in plasma samples (200 μL) is now precipitated with acetonitrile (400 μL) containing the internal standard (2-naphthoic acid). The supernatant is analysed at excitation and emission wavelengths of 320 and 380 nm, respectively as in the previous method. A Luna C18 column (Phenomenex, Australia) at 40 °C with mobile phase of glacial acetic acid (0.032%) in acetonitrile:water (60:40, v:v), an injection volume of 10 μL and a flow rate of 1.5 mL/min is employed. Analysis time is 8 min. Calibration curves in drug-free plasma range from 0.005 to 10.00 μg/mL. Data points are fitted using linear regression with a weighting factor of 1/concentration. The inter-day accuracy and imprecision of the quality control samples (0.0075, 0.015, 3.00 and 9.80 μg/mL) is 90–115% and ≤ 14.5%, respectively. •This modified method requires less plasma per sample and displays less imprecision and a lower assay limit.•The assay has been validated and now exceeds quality criteria set by the FDA standards.•Little febuxostat (11%) was associated with blood cells confirming the suitability of plasma for pharmacokinetic studies.•The majority of febuxostat (85%) is eliminated from the plasma in the first 9 h.•Extensive stability studies have been performed over a variety of potential clinical study related conditions.•The enhanced HPLC assay enables more detailed pharmacokinetic-pharmacodynamic investigations of the drug.