A liquid chromatography with tandem mass spectrometry（LC-MS/MS） method has been developed and validated for the measurement of sunitinib in rabbit plasma. After protein precipitation with acetonitrile, samples were analyzed on a Zorbax Extend-C18 column（150 mm×4.6 mm, 5μm）. The mobile phase consisted of a mixture of acetonitrile and deionized water（containing 0.05% formic acid） at a ratio of 27：73（v/v）, and the flow rate was set at 0.8 mL /min. The column temperature was maintained at 30 oC. The LC eluate was detected by an electrospray ionization（ESI） source operated in the positive ion mode, and quantification was conducted using MRM of the transitions m/z 399.24→283.01 and m/z 415.19→178.00 for sunitinib and internal standard（IS, diltiazem hydrochloride）, respectively. The calibration curve was linear in the range of 2–600 ng/m L. The lower limit of quantification was 2 ng/mL. The method also exhibited satisfactory results in terms of sensitivity, specificity, accuracy（with relative error ranging from –4.0% to 1.1%）, precision（with intra- and inter-day relative standard deviations ranging from 2.8% to 9.5%）, matrix effect, recovery as well as stability. Taken together, our newly developed method was reliable to monitor sunitinib concentrations in rabbit plasma.
