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 µm, and the diameter of 89.93% of all microspheres ranged from 7.0 µm to 30.0 µm. 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(1/2β)) 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 ∞ (AUC(0-∞)) was increased from 11.66 h·µg/g to 508.00 h·µg/g. The peak concentration (C(max)) in lung was increased from 5.95 µg/g to 93.36 µg/g. Three lung-targeting parameters were further assessed and showed that the microspheres had remarkable lung-targeting capabilities.