Metabolism and excretion kinetics of 14C-labeled and non-labeled difloxacin in pigs after oral administration, and antimicrobial activity of manure containing difloxacin and its metabolites

Fluoroquinolones are amongst the most important antibiotics used in veterinary medicine. On this account the behavior of difloxacin (DIF) and its metabolites was investigated by administering the 14C-labeled and non-labeled veterinary drug to fattening pigs. The excretion kinetics were determined after daily collection of manure. Sarafloxacin (SAR) was found to be the major metabolite, three further trace metabolites were also recovered, applying high-resolution (HR) mass spectrometric technique. The identification of DIF and SAR was confirmed by comparison with the spectroscopic and chromatographic data of the authentic references. The identification of the three trace metabolites was performed by HR-MS/MS. Only 8.1% of the administered radioactivity remained in the pig after 10 days and DIF accounted for 95.9% of the radioactivity excreted. More than 99% of the labeled compounds were detected and identified in the manure. The mean recoveries for all single electrolytes were ⩾94%. Linearity was established over concentration range 10–10,000 μg/kg manure with a correlation coefficient ⩾0.99. By using in vitro antimicrobial activity tests against a group of standard pathogenic control strains, the results showed that the residual antibiotic concentrations in the manure of pigs are high enough to exhibit antibacterial activity.