Micelle-Enhanced conventional and synchronous spectrofluorimetric methods for the simultaneous determination of lesinurad and febuxostat: Application to human plasma

A simple synchronous spectrofluorimetric method was developed for simultaneous determination of lesinurad and febuxostat. The investigated drugs were measured at 294 and 329 nm, respectively in the presence of each other without interference at Δλ of 50 nm (Method I). The different experimental parameters affecting the fluorescence intensities were carefully studied and optimized. The maximum synchronous fluorescence intensities were obtained at pH 6.5 using borate buffer and distilled water was used as a diluting solvent. Excellent linearity ranges were obtained using 20.0–500.0 ng mL−1 and 1.0–80.0 ng mL−1 for lesinurad and febuxostat, respectively. The method exhibited high sensitivity with detection limits down to 4.0 ng mL−1 and 0.01 ng mL−1 and quantitation limits down to 12.12 ng mL−1 and 0.02 ng mL−1, respectively. Recovery percentages ranged from 97.68 to 103.37% were obtained upon spiking of human plasma samples, indicating high bioanalytical applicability. Concerning Method II, methanolic solution of lesinurad was measured spectroflourimetrically with λexcitation at 290 nm and λemission at 341 nm with high sensitivity using borate buffer of pH 6.5 and methanol as a diluting solvent. A considerable enhancement of the fluorescence intensity was achieved by using 1.0% w/v cetremide as a micellar system. The method was rectilinear over the concentration range of 3.0–80.0 ng mL−1 with detection and quantitation limits down to 0.47 and 1.42 ng mL−1, respectively. The developed method was efficiently applied for the estimation of the cited drug in spiked human plasma with high recovery percentages (98.58–101.64%). The methods were validated according to the ICH guidelines and further applied to commercial tablets with good results.