Validated LC–MS/MS assay for the determination of felbinac: Application to a preclinical pharmacokinetics study of felbinac trometamol injection in rat

A rapid and sensitive analytical method based on high-performance liquid chromatography–tandem mass spectrometry (LC–MS/MS) has been developed for the determination of felbinac in rat plasma, bile, urine, feces and tissue. Sample preparation involved liquid–liquid extraction with ethyl ether–dichloromethane (60:40, v/v). Chromatography of felbinac and the internal standard probenecid was performed within 2 min on a Venusil MP C18 column (100 mm × 4.6 mm i.d., 5 μm) with a mobile phase consisting of acetonitrile–5 mM ammonium acetate containing 0.1% formic acid (pH 3.0) (80:20, v/v) at a flow rate of 1.2 ml/min. Detection by electrospray negative ionization mass spectrometry and multiple-reaction monitoring of the transitions of felbinac at m/z 211.1 → 167.0 and of probenecid at m/z 283.9 → 239.9 was linear over the concentration range 5–5000 ng/ml with a lower limit of quantitation of 5 ng/ml using a sample volume of only 50 μl. Intra- and inter-day precisions (as relative standard deviation, R.S.D.) were ≤7.3% and ≤6.4%, respectively, and accuracy (as relative error, R.E.) was in the range −2.1 to 7.4%. Recoveries and matrix effects were satisfactory in all the biological matrices examined. The method was applied to a preclinical pharmacokinetic study in rat involving a single intravenous injection of felbinac trometamol.