Pharmacokinetics of tildipirosin in pig tonsils

The penetration of antimicrobials in pig tonsils is hardly known. The objective of the study was to quantify the tildipirosin (TD) penetration in tonsils. Animals were randomly divided into six groups (control, T1, T2 (1), T2(5), T2(10), and T2(15)) of eight animals. T1 and T2 groups received a dose of 2 and 4mg of TD/kg bw in one shot (Zuprevo((R)) MSD Animal Health), respectively, and the control group received 2mL of saline solution. The animals were sacrificed by intravenous administration of pentobarbital sodium 24h after finishing the treatment for the control, T1, and T2(1) groups, whereas animals of T2(5), T2(10), and T2(15) groups were sacrificed at 5, 10, and 15days, post-treatment, respectively. Tonsils and blood samples were taken at necropsy to obtain plasma, and the tildipirosin concentration was determined by high-performance liquid chromatography with tandem mass spectrometry detection. The concentration in plasma was always significantly lower than in tonsil. Average TD tonsil concentrations increased significantly in a dose-dependent manner, and the tonsil TD vs. plasma TD concentration ratio was approximately 75 for the doses of 2 and 4mg of TD/kg bw at 24h post-treatment. Moreover, the maximum concentration of tildipirosin in tonsil was observed at 1day postadministration, and this concentration decreased gradually from this day until 15days postadministration for the dose of 4mg of TD/kg bw. Finally, the ratio AUC(tonsil)/AUC(plasma) was 97.9, and the T-1/2 (h) was clearly higher in tonsil than in plasma.