Preparation and evaluation of enrofloxacin microspheres and tissue distribution in rats

New enrofloxacin microspheres were formulated, and their physical properties, lung-targeting ability, and tissue distribution in rats were examined. The microspheres had a regular and round shape. The mean diameter was 10.06 mu m, and the diameter of 89.93% of all microspheres ranged from 7.0 mu m to 30.0 mu m. Tissue distribution of the microspheres was evaluated along with a conventional enrofloxacin preparation after a single intravenous injection (7.5 mg of enrofloxacin/kg bw). The results showed that the elimination half-life (t(1/2 beta)) of enrofloxacin from lung was prolonged from 7.94 h for the conventional enrofloxacin to 13.28 h for the microspheres. Area under the lung concentration versus time curve from 0 h to infinity (AUC(0-infinity)) was increased from 11.66 h.mu g/g to 508.00 h.mu g/g. The peak concentration (C-max) in lung was increased from 5.95 mu g/g to 93.36 mu g/g. Three lung-targeting parameters were further assessed and showed that the microspheres had remarkable lung-targeting capabilities.