Pharmacokinetics and lung-targeting characterization of a newly formulated enrofloxacin preparation

A new lung-targeting and controlled releasing preparation, enrofloxacin microsphere, was formulated and its physical properties, stability, pharmacokinetics and lung-targeting characteristics were tested in this study. The enrofloxacin microsphere prepared was demonstrated round and regular, which was easy to be dispersed and stable in both light stability test and heat stability test. Following intravenous administration of a single dose in dog, the drug concentration-time data in the lung were fitted most suitably with three-compartment open model. Compared with enrofloxacin injection (Baytril, half-life of distribution phase in the lung was shortened from 0.72 to 0.16 h, half-life of elimination phase in the lung was prolonged from 5.15 to 33.86 h and clearance of drug concentration in the lung was decreased from 0.603 to 0.267 L/h/kg. Lung-targeting parameters, including the relative intake rate (Re), targeting efficacy (Te) and the ratio of peak concentration (Ce), were calculated according to the pharmacokinetic parameters. The results showed that Re (2.48) and Ce (4.27) of the lung was much greater than that of other tissues and the ratio of Te(microsphere) to Te(Baytril) increased by a factor of 1.77 (compared with liver) to 3.51 (compared with spleen). Therefore, the enrofloxacin microsphere prepared in this study had controlled releasing and lung-targeting effects in dog.