MILK, SERUM, AND MAMMARY TISSUE CONCENTRATION OF PIRLIMYCIN FOLLOWINGINTRAMUSCULAR, INTRAMAMMARY, OR COMBINATION THERAPY OF CHRONIC STAPHYLOCOCCUS-AUREUS MASTITIS

Pirlimycin, a lincosaminide antibiotic currently under development as a mastitis therapeutic, was evaluated under different treatment regime ns for antimicrobial activity against chronic Staphylococcus aureus ma stitis. Treatment regimens included: a) intramuscular injection of 1 m g/kg pirlimycin. b) intramammary infusion of 50 mg pirlimycin in an aq ueous gel, and c) combination of both intramuscular and intramammary t herapy. Two treatments were administered at 24-hour intervals. Combina tion therapy and intramammary infusion resulted in a greater decrease in S. aureus colony forming units in milk and mammary tissue and resul ted in higher concentrations of pirlimycin than intramuscular injectio n alone. Pirlimycin passed well from serum into milk; however, concent rations in milk after intramuscular injection alone were below the min imum inhibitory concentration for S. aureus. Although S. aureus number s were greatly reduced during the first 48 hours after treatment, viab le organisms were still present, indicating that increasing the concen trations of intramuscular and intramammary doses or reducing the inter val between doses may be needed to cure chronic S. aureus mastitis.