Efficacy of Enrofloxacin in the Treatment of Bovine Clinical Mastitis

Abstract

Fluoroquinolones form a promising family of new bactericidal antimicrobials. Enrofloxacin is the first antimicrobial of this family available to veterinary medicine. Fluoroquinolones share a wide spectrum of acitivity but are most potent against gram-negative bacteria. They have a large volume of distribution and a low binding to plasma proteins, and are active at low concentrations. Compared with many other antimicrobials, they also have the advantage of being active against intracellular pathogens (8). Very few studies have been made of the pharmacokinetics of enrofloxacin in lactating cows. In one report, enrofloxacin was administered intravenously ( IV) or intramuscularly (IM) to three cows (3). After both routes of administration, the concentration of enrofloxacin in milk rapidly exceeded that in plasma. At a dose of 2.5 mg/kg b.w., inhibitory levels against coliform bacteria and most staphylococci(> 0.25 μg/ ml) were obtained in milk for approximately 24 hours. Using the same dose administered subcutaneously (SC), a concentration of 0.06 μg/ml or more was maintained in the serum and tissue of calves for 24 hours (6). The bactericidal action of fluoroquinolones, their wide distribution in tissue and their activity against intracellular pathogens make them attractive for the treatment of staphylococcal mastitis. Enrofloxacin could solve the problem posed by the lack of a pharmacokinetically suitable antimicrobial for coliform mastitis. There are no published data on the efficacy of fluoroquinolones in the treatment of mastitis, except one preliminary report on norfloxacin in dry cow therapy (7).