Cefoperazone sodium preparation behavior after intramammary administration in healthy and infected cows

Selection of the antimicrobial agent and maintenance of adequate drug concentrations at the site of infection are the most relevant problems in mastitis antibiotic therapy. Intramammary drug efficacy can be maximized by keeping drug concentrations at the site of infection above the minimum inhibitory concentration (MIC) as long as possible; the most important pharmacokinetic and pharmacodynamic (PK/PD) measure for efficacy evaluation is time during which drug concentrations exceed the MIC (t > MIC). To evaluate this measure, the PK profile of cefoperazone (CFP) after single intramammary administration in healthy and subclinical infected Staphylococcus aureus cows and the MIC of Staph. aureus field strains were assessed. In addition, the degree of drug passage from udder to bloodstream was investigated by measuring systemic drug absorption in healthy and infected animals. Cefoperazone concentrations were quantified by HPLC in quarter milk samples and blood serum samples. Systemic drug absorption was negligible in healthy animals (0.020 +/- 0.006 mu g/mL serum at 4 h), whereas it was higher in infected animals (0.102 +/- 0.079 mu g/mL at 4 h and 0.025 mu g/mL at 24 h), probably due to the damage of epithelial cell junctions caused by subclinical infections. The MIC90 value for CFP in Staph. aureus field strains (n = 24) was 0.64 mu g/mL. The PK/PD evaluation, determined by t > MIC, showed a longer persistence of CFP in infected quarters than in healthy ones (mean residence time was 8.37 +/- 1.51 vs. 11.42 +/- 5.74 h in September and 2.07 +/- 0.43 vs. 3.31 +/- 0.91 h in October), with a t > MIC of 45 +/- 6 h for infected quarters versus 38 +/- 5 h for healthy quarters different only in October. This could mean a prolonged time in which microorganisms are exposed to drug activity and thus, a greater efficacy of the drug.