Abstract
A rapid, simple and sensitive liquid chromatography/tandem mass spectrometry (LC–MS/MS) assay was developed for the determination of dexamethasone (Dex) and dexamethasone sodium phosphate (Dex SP) in plasma and human cochlear perilymph. After proteins were precipitated with a mixture of acetonitrile and methanol, Dex, Dex SP and flumethasone, the internal standard, were resolved on a C18 column using gradient elution of 5mM ammonium acetate and methanol. The three compounds were detected using electrospray ionisation in the positive mode. Standard curves were linear over the concentration range 0.5–500μg/L (r>0.99), bias was <±10%, intra- and inter-day coefficients of variation (imprecision) were <10%, and the limit of quantification was 0.5μg/L for both Dex and Dex SP. The assay has been used successfully in a clinical pharmacokinetics study of Dex and Dex SP in cochlear perilymph and plasma.