Inefficacy of enrofloxacin in the elimination of Pasteurella multocida in rabbits

The administration of enrofloxacin (5 mg/kg subcutaneously every 12 h for 10 days) failed to eliminate Pasteurella multocida from all naturally and experimentally infected rabbits. Although the enrofloxacin concentrations in serum and in turbinate bones were greater than the determined minimal inhibitory concentrations, P. multocida could be detected in nasal cavities, turbinates, trachea, middle ear and outer ear of experimentally infected rabbits after treatment. It is to be supposed that P. multocida colonizes organs or tissues in which an effective enrofloxacin concentration cannot be achieved. Such sites could be the paranasal sinuses, the auditory tube and the middle ear. This finding underlines the indispensibility of in vivo testing of antibiotic effectiveness.