A liquid chromatography-tandem mass spectrometry method for the quantitation of actarit in rabbit plasma: application to pharmacokinetics and metabolic stability.

Actarit (ATR), 4-acetylaminophenylacetic acid is an orally effective disease-modifying anti-rheumatic drug widely prescribed for the treatment of rheumatoid arthritis. The present study demonstrates the first report on a selective and sensitive liquid chromatography-tandem mass spectrometry method for the quantification of ATR in rabbit plasma using p-coumaric acid as an internal standard (IS). Following liquid-liquid extraction, chromatographic separation of the reconstituted samples was achieved isocratically on a Syncronis-C18 column with a mobile phase consisting of aqueous ammonium acetate (10mM, pH4)- methanol and acetonitrile mixture (8:92, v/v) at a flow rate of 0.6ml/min. ATR and IS were detected using electrospray ionization operated in negative multiple reaction monitoring mode. The calibration curve was linear (r(2)0.990) over the concentration range of 1-4000ng/ml with a lower limit of quantitation of 1ng/ml. The mean extraction recovery of ATR and IS from rabbit plasma was greater than 85%. The method complied well with US Food and Drug Administration guidelines for selectivity, sensitivity, accuracy, precision, matrix effect, dilution integrity, carry-over effect and stability. The method was successfully applied to in vitro metabolic stability (using rabbit liver microsomes) and in vivo pharmacokinetic study after oral administration of ATR at a dose of 10mg/kg in New Zealand rabbits. Copyright (c) 2015 John Wiley & Sons, Ltd.