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 x 4.6 mm, 5.0 microm) 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 <or=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 5h at room temperature (about 20 degrees C) and they are also stable after freeze-thaw cycles. The method was successfully applied to the pharmacokinetic studies of lefucoxib in rats.