Ex Vivo Pharmacokinetics and Pharmacodynamics Modeling and Optimal Regimens Evaluation of Cefquinome Against Bovine Mastitis Caused by Staphylococcus aureus

Cefquinome, the fourth-generation cephalosporin applied solely for veterinary medicine, is commonly used for bovine mastitis caused by Staphylococcus aureus. The present study aims to establish an optimal dose and provide a PK/PD Cutoff value (CO(PD)) for cefquinome against S. aureus based on ex vivo pharmacokinetics and pharmacodynamics (PK/PD) integration. This study investigated the pharmacokinetics (PK) of cefquinome when administered as three consecutive intramammary (IMM) doses of cefquinome in three healthy dairy cows at 75 mg/gland. Drug concentration was determined by HPLC-MS/MS assay. The ex vivo pharmacodynamics (PD) of cefquinome were evaluated by using a milk sample from a PK experiment. The relationship between the AUC/ MIC of cefquinome and bacterial loading reduction was simulated using a Sigmoid Emax model. The cefquinome concentration in milk attained a maximum level of 1.55 ± 0.21 mg/mL at 1.8 h after the third administration. The mean value of the area under the concentration-time curve (AUC(0−24)) was 26.12 ± 2.42 mg·h/mL after the third administration. The elimination half-life was 10.6 h. For PD profile, the MICs of cefquinome in milk were 2–4 times higher than those in the broth. In vitro time-killing curve shows that initial bacterial concentration has a huge impact on antibacterial effect on three strains. The antibacterial effect was weakened with the initial bacterial concentration increasing from 10(6) to 10(8) CFU/mL. The AUC(0−24h)/MIC index correlated well with ex vivo efficacy both for the initial inoculum of 10(6) CFU/mL and 10(8) CFU/mL (R(2) > 0.84). According to the inhibitory sigmoid E(max) model analysis, the PK/PD surrogate (AUC(0−24)/MIC) values were 8,638, 1,397, and 3,851 for bactericidal effect (E = −3) with an initial inoculum of 10(6) CFU/mL, while the corresponding values were 12,266, 2,295, and 5,337, respectively, with the initial inoculum of 10(8) CFU/mL. The ex vivo PK/PD based population dose prediction indicated a target attainment rate (TAR) of 90% of 55 mg/gland/12 h. The CO(PD) for cefquinome against S. aureus was 2 μg/mL under the recommended dose of 55 mg/gland/12 h. However, it should be validated in clinical practice in future investigations. These results contribute to the rational use of cefquinome for mastitis treatment in clinical veterinary medicine.