Quantification of epimeric budesonide and fluticasone propionate in human plasma by liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry.

A highly sensitive and selective liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry assay was developed and validated for simultaneous determination of epimeric budesonide (BUD) and fluticasone propionate (FP) in plasma. The drugs were isolated from human plasma using C18 solid-phase extraction cartridges, and epimeric BUD was acetylated with a mixture of 12.5% acetic anhydride and 12.5% triethylamine in acetonitrile to form the 21-acetyl derivatives following the solid-phase extraction. Deuterium-labelled BUD acetate with an isotopic purity >99% was synthesized and used as the internal standard. The assay was linear over the ranges 0.05-10.0 ng/ml for epimeric BUD, and 0.02-4.0 ng/ml for FP. The inter- and intra-day relative standard deviations were <14.3% in the assay concentration range.