Liquid chromatography tandem mass spectrometry determination of total budesonide levels in dog plasma after inhalation exposure

A sensitive and selective method to quantify budesonide in dog plasma samples was developed and fully validated. Liquid–liquid extraction was followed by solid-phase extraction and liquid chromatography–tandem mass spectrometry with electrospray ionization. After reconstitution of the analytes in the mobile phase, samples were analysed by reversed-phase liquid chromatography with isocratic elution. d8-Budesonide was used as an internal standard, and characteristic transitions of d8-budesonide and budesonide were used for quantification. The method was validated with respect to selectivity, specificity, linearity, recovery, repeatability, reproducibility and limits of detection and quantification. The validated method was successfully applied to monitor the plasma levels of budesonide in dogs exposed to clinical doses of inhaled and intravenous drug.