Determination of lefucoxib in rat plasma, urine, and feces by high-performance liquid chromatography with fluorescence detection: Application in pharmacokinetic studies

A sensitive, specific, and reproducible high-performance liquid chromatography (HPLC) method with fluorescence detection was developed for determination of lefucoxib in rat plasma, urine, and feces. The method involved liquid–liquid extraction using methyl tert-butyl ether, and celecoxib was used as the internal standard. The chromatographic separation was performed on a Kromasil C18 column (250.0 mm × 4.6 mm, 5.0 μm) with a mobile phase gradient consisting of water and methanol at a flow rate of 1 ml min−1. The assay was linear in the range of 5.0–1000.0 ng ml−1 with a correlation coefficient (r) of 0.9994. The limit of quantification was 5.0 ng ml−1. Inter- and intra-assay precisions were ≤14.2% and 5.5%, respectively. Relative recoveries ranged from 97.9% to 108.1%, and absolute recoveries were about 70.0% both with and without internal standard. All biological matrices (plasma, urine, and fecal homogenate) containing lefucoxib were stable for 5 h at room temperature (about 20 °C) and they are also stable after freeze–thaw cycles. The method was successfully applied to the pharmacokinetic studies of lefucoxib in rats.