Preparation and evaluation of enrofloxacin microspheres and tissue distribution in rats

Abstract

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 (t1/2β) 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 ∞ (AUC00∞) was increased from 11.66 h·µg/g to 508.00 h·µg/g. The peak concentration (Cmax) 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.

Keywords: enrofloxacin; lung-targeting; microsphere; preparation; tissue distribution.

Fig. 1. (A) Optical photomicrograph of the enrofloxacin microspheres (ENR-MICs). (B) Scanning electron microscopy micrograph of the ENR raw material. (C) Scanning electron microscopy micrograph of an ENR-MIC. Scale bar = 50 µm. Magnification: 100× (A), 150× (B), 3000× (C).

Fig. 2. Particle size distribution of the ENR-MICs. Size distribution was determined using 800 particles chosen randomly.

Fig. 3. In vitro drug release results for the ENR-MICs and ENR raw material (mean ± SD, n = 3).

Fig. 4. Semilogarithmic plots showing the mean ± SD plasma and tissue concentrations of ENR vs. time in rats (n = 6) after intravenous administration of the ENR-MICs (7.5 mg/kg bw).

Fig. 5. Semilogarithmic plots showing the mean ± SD plasma and tissue concentrations of ENR vs. time in rats (n = 6) after intravenous administration of the ENR-INJ (7.5 mg/kg bw).