The pharmacokinetics of dexamethasone (DEX) were investigated after an intravenous (IV) or intramuscular (IM) bolus injection of 0.3mg/kg bodyweight DEX sodium phosphate in pigs. The plasma concentrations of DEX were determined using a validated high-performance liquid chromatography–tandem mass spectrometry (LC–MS/MS) method and the pharmacokinetics were determined by one-compartmental analysis.The mean area under the plasma concentration–time curve and the mean elimination half-life were 133.07±39.59ng.h/mL and 0.77h, and 173.24±53.59ngh/mL and 1.06h following IV and IM administration, respectively. The volume of distribution and clearance recorded after IV administration were 2.78±0.88L/kg and 2.39±0.57L/hkg, respectively.An IM bolus injection of DEX sodium phosphate in pigs resulted in a fast and complete absorption, with a mean maximal plasma concentration of 80.94±21.29ng/mL at 0.35±0.21h and a high absolute bioavailability of 131.06±26.05%.