Pharmacokinetics of levofloxacin in non-lactating goats and evaluation of drug effects on resistance in coliform rectal flora.

This study aimed to evaluate the pharmacokinetics/pharmacodynamics (PK/PD) of levofloxacin in non-lactating goats. Using a randomized cross-over study design, each group of animals (n = 7) received 2 mg/kg of levofloxacin intravenously (IV) and subcutaneously (SC). Plasma concentrations of levofloxacin were quantified by High Performance Liquid Chromatography with fluorescence detector (HPLC-FL). Rectal swabs were collected prior and after the treatment to identify the main bacterial population and to evaluate in vitro antimicrobial susceptibility using minimal inhibitory concentration (MIC) method. Mean values of terminal half-life for IV and SC groups were 4.56 and 5.14 h, respectively. After SC administration, the peak plasma concentration was achieved at 2 h, with a Cmax of 3681 ng/mL. Mean bioavailability was 92.12%. Bacteria isolation showed the presence of Escherichia coli (E. coli) that quickly becomes resistant to levofloxacin potentially rendering the drug ineffective. Results seem to suggest that levofloxacin is able to reach considerable plasma concentrations after both IV and SC administration, but it must be considered that both routes of administration can lead to a reversible selection of resistance in gastro-intestinal bacteria.