Abstract: AIM: To establish an LC-MS/MS method for the determination of torasemide in Beagle dog plasma,and study the relative bioavailability of the torasemide sustained release tablets.METHODS: A reversed phase HPLC column of Waters Symmetry-C₁₈ (100 mm×4.6 mm, 5 μm) was used in the experiment.Acetonitrile-20 mmol/L ammonium formate (65∶35,V/V) was used as mobile phase at the flow rate of 0.4 mL/min, the column temperature was set at 30 ℃. A single oral dose of 5 mg torasemide release tablets or reference tablets were given to 6 Beagle dogs in an open randomized two way crossover design.The concentrations of plasma samples collected at the different time were determined by LC-MS/MS method.RESULTS: With the linear range of 0.02-5 μg/mL and the lower limit quantification of 0.02 μg/mL, the LC-MS/MS method had high sensitivity, stability and specificity. The main pharmacokinetic parameters of test sustained release tablets and reference tablets were as follows:the C_max were (2.6±0.5) μg/mL and (3.0±0.6) g/mL,the t_max were (3.3±1.4) h and (1.2±0.8) h,the AUC_{0-48 h} were (36.1±11.0) μg·h·mL^-1 and (32.1±13.1) μg·h·mL^-1. Compared to regular tablets,the bioavailability of sustained release tablets was (118.0±28.3)%.CONCLUSION: The method is simple, accurate and robust for the determination of torasemide in Beagle dog plasma, and successfully applied it to the bioavailability evaluation of torasemide sustained release tablets given to Beagle dogs.

Key words: Torasemide, LC-MS/ MS, Relative bioavailability