Drug selection and use in mastitis: systemic vs local therapy.

The optimal properties of antibacterial drugs, (administered parenterally or intracisternally during clinical mastitis) required for achieving and maintaining effective drug concentrations at the site of infection are reviewed. The in vitro sensitivity of the udder pathogen, expressed as the minimal inhibitory concentration (MIC) of the drug, and the physicochemical properties of the antibiotic are major determinants in the duration of effective drug concentrations in the udder. Injectable oxytetracycline and chloramphenicol possess limited IM bioavailability properties, and therefore, should be administered IV. Effective passage of drug from blood into the udder is best achieved with the macrolide antibiotics, but the antibacterial spectra of these drugs are limited to gram-positive pathogens. For intramammary treatment, drugs that are distributed throughout the udder and are quickly absorbed into the general blood circulation should be preferred. A second priority should be given to those drugs possessing more limited distribution characteristics. Some of the most active drugs in vitro are poorly and unevenly distributed in the udder and are absorbed only to a limited extent.