Development and validation of an LC-MS/MS method for the determination of mesalazine in beagle dog plasma and its application to a pharmacokinetic study.

A simple, specific and sensitive LC-MS/MS method was developed and validated for the determination of mesalazine in beagle dog plasma. The plasma samples were prepared by protein precipitation, then the separation of the analyte was achieved on a Waters Spherisorb C6 column (150 × 4.6 mm, 5 µm) with a mobile phase consisting of 0.2% formic acid in water-methanol (20:80, v/v). The flow rate was set at 1.0 mL/min with a split ratio of 3:2. Mass spectrometric detection was achieved by a triple-quadrupole mass spectrometer equipped with an electrospray source interface in positive ionization mode. Quantitation was performed using selected reaction monitoring of precursor-product ion transitions at m/z 154 → m/z 108 for mesalazine and m/z 285 → m/z 193 for diazepam (internal standard). The linear calibration curve of mesalazine was obtained over the concentration range 50-30,000 ng/mL. The matrix effect of mesalazine was within ±9.8%. The intra- and inter-day precisions were <7.9% and the accuracy (relative error) was within ±3.5%. The validated method was successfully applied to investigate the pharmacokinetics of mesalazine in healthy beagle dogs after rectal administration of mesalazine suppository.