Liquid chromatography–mass spectrometric method for the sensitive determination of niflumic acid in human plasma and its application to pharmacokinetic study of talniflumate tablet

A sensitive LC–MS method was developed and validated for the determination of niflumic acid (NFA), the active metabolite of the talniflumate formulation, in human plasma. The analyses were performed on C18 column using acetonitrile–ammonium acetate buffer (pH 5.7, 40:60) as a mobile phase with quadrupole MS detection of NFA at m/z 281 in a negative ion-monitoring mode. Calibration curve was linear in the concentration range of 1–1000 ng/mL in human plasma. The higher sensitivity of LC–MS allowed low concentrations of NFA to be determined at initial drug absorption and terminal elimination phases following oral administration of talniflumate tablet.