Antibiotics in Treatment of Mastitis

Antibiotics have failed early expectations of chemosterilization of the mammary gland. Treatment before bacterial identification necessitates use of broad-spectrum drugs. Cure rates vary with the pathogen: low for Staphylococcus aureus, high for Streptococcus agalactiae . The most effective antibiotics against Gram-negative bacilli are not approved for U.S. use. During lactation, therapy is usually limited to clinical cases, eliminating clinical signs in 90% of cases but achieving many fewer bacteriologic cures. Mass intramammary treatment at the end of lactation is common. Higher cure rates due to higher drug concentrations and long retention in the gland, plus avoidance of milk discard are advantages. Some degree of prophylaxis is afforded against the high new infection rate in the early nonlactating period. Evidence conflicts as to increased resistance to antibiotics as a result of mastitis treatment, but has been reported for populations of staphylococci, streptococci and coliform bacteria.