DETERMINATION OF PLASMA-LEVELS OF EXEMESTANE (FCE-24304), A NEW IRREVERSIBLE AROMATASE INHIBITOR, USING THERMOSPRAY LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY

A high performance liquid chromatographic mass spectrometric method with thermospray ionization for the determination of concentrations of exemestane (6-methylenandrosta-1,4-diene-3,17-dione FCE 24304) in human plasma has been developed. The sensitivity of the method allowed the determination of exemestane concentrations as low as 1 ng ml(-1). A suitable internal standard was used for quantification. The intra-day precision (relative standard deviation, R.S.D.) ranged from 16.3% near to the lower limit of quantification to 0.3% close to the upper end of the calibration graph. The mean accuracy of the method was found to be 97.8% (R.S.D. = 7%). Unlike a previously developed gas chromatographic/mass spectrometric method, the new method proved to be suitable for the determination of unchanged drug plasma levels in exemestane-treated subjects.