Determination of gefitinib in plasma by liquid chromatography with a C12 column and electrospray tandem mass spectrometry detection

A highly sensitive liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS/MS) method has been developed for the measurement of gefitinib (ZD 1839) in human plasma. The method was validated over a linear ran-e of 0.5-1000 ng/mL, using deuterated gefitinib (D-8-ZD1839) as the internal standard (IS). Compounds were extracted from 500 muL of sodium heparin plasma by 6.0 mL butyl methylether liquid-liquid extraction. The dried residue was reconstituted with 250 muL of 20% acetonitrile with 1.0% formic acid and 30 muL injected onto the LC-ESI-MS/MS system. Chromatographic separation was achieved on a Phenomenex(R) Synergi 4mu MAX-RP 80 Angstrom C-12 column (75 x 2.0 mm(2)) with an isocratic mobile phase of acetonitrile-1.0% formic acid (30:70, v/v). The analytes were detected with a PE Sciex API 365 triple quadrupole mass spectrometer using turbo ion spray(R) source with positive ionization. Ions monitored in the multiple reaction monitoring (MRM) mode were m/z 447.2 (precursor ion) to m/z 127.8 (product ion) for gefitinib and m/z 455.2 (precursor ion) to m/z 136.0 (product ion) for D-8-ZD1839. The lower limit of quantitation (LLOQ) of gefitinib was 0.30 ng/mL (S/N greater than or equal to 10), and results from a 5-day validation study demonstrated acceptable within-day and between-day precision (CV% values less than or equal to6.0% and less than or equal to5.2%, respectively) and accuracy (range 91.0-97.7%). This method is now used to analyze plasma samples from pediatric pharmacokinetic studies of ZD1839, and the wide linear range (similar to4 log) of this method provides a distinct advantage, as shown by the results of a representative patient.