Pharmacokinetics and pharmacodynamics of intramammary cefquinome in lactating goats with and without experimentally induced Staphylococcus aureus mastitis

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 (COPD) 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 (AUC0−24) 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 106 to 108 CFU/mL. The AUC0−24h/MIC index correlated well with ex vivo efficacy both for the initial inoculum of 106 CFU/mL and 108 CFU/mL (R2 > 0.84). According to the inhibitory sigmoid Emax model analysis, the PK/PD surrogate (AUC0−24/MIC) values were 8,638, 1,397, and 3,851 for bactericidal effect (E = −3) with an initial inoculum of 106 CFU/mL, while the corresponding values were 12,266, 2,295, and 5,337, respectively, with the initial inoculum of 108 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 COPD 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.

Disposition of Cefquinome in Turkeys (Meleagris gallopavo) Following Intravenous and Intramuscular Administration

The bioavailability and pharmacokinetics in turkeys of cefquinome (CFQ), a broad-spectrum 4th-generation cephalosporin antibiotic, were explored after a single injection of 2 mg/kg body weight by intravenous (IV) and intramuscular (IM) routes. In a crossover design and 3-weeks washout interval, seven turkeys were assigned for this objective. Blood samples were collected prior to and at various time intervals following each administration. The concentration of CFQ in plasma was measured using HPLC with a UV detector set at 266 nm. For pharmacokinetic analysis, non-compartmental methods have been applied. Following IV administration, the elimination half-life (t_1/2ʎz), distribution volume at steady state (Vd_ss), and total body clearance (Cl_tot) of CFQ were 1.55 h, 0.54 L/kg, and 0.32 L/h/kg, respectively. Following the IM administration, CFQ was speedily absorbed with an absorption half-life (t_1/2ab) of 0.25 h, a maximum plasma concentration (C_max) of 2.71 μg/mL, attained (T_max) at 0.56 h. The bioavailability (F) and in vitro plasma protein binding of CFQ were 95.56% and 11.5%, respectively. Results indicated that CFQ was speedily absorbed with a considerable bioavailability after IM administration. In conclusion, CFQ has a favorable disposition in turkeys that can guide to estimate optimum dosage regimes and eventually lead to its usage to eradicate turkey's susceptible bacterial infections.

PK/PD integration and pharmacodynamic cutoff of cefquinome against cow mastitis due to Escherichia coli

Cefquinome is the fourth generation of cephalosporin approved solely in animal usage. In order to slow down the resistance development of E. coli to cefquinome, and to protect and maintain the effectiveness of cefquinome, an ex vivo PK/PD modeling of cefquinome against E. coli in cows after intramammary infusion administration was conducted. The epidemiologic cutoff (ECOFF) and pharmacodynamic cutoff (COPD) of cefquinome against E. coli in lactation cows after intramammary infusion administration were recommended. The MICs of cefquinome against 1073 clinical E. coli isolates ranged from 0.015 to >64 μg/ml, and the ECOFF was defined as 0.125 μg/ml. The pharmacokinetic results showed that cefquinome maintained high concentration in milk for a long period with the T_1/2β of 10.60 h after intramammary infusion in dairy cows. The drug concentration in skimmed milk was still as high as 0.15 mg/ml after 48 h. Cefquinome displayed bacterial killing effect at 2× MIC with the initial inoculum of 10⁶  cfu/ml in vitro; however, the same effect was attained with a concentration as high as 32× MIC with the initial inoculum of 10⁸  cfu/ml both in artificial medium and in skimmed milk. The initial inoculum is an important factor on time-killing curve accounting for weakened killing pattern of cefquinome. The AUC_0-24 h /MIC index correlated well with ex vivo efficacy. The AUC_0-24 h /MIC values for bactericidal effect were 50, 016, and 67,644, respectively, for initial inoculum of 10⁶ and 10⁸  cfu/ml, indicating the bacterial loading or the severity of infection would infect the PK/PD modeling results. The ex vivo PK/PD-based population dose prediction indicated a target attainment rate (TAR) at the existing daily dose (75 mg/udder) of 84.77% against E. coli. Thus, it was recommended as rational dosage. The COPD of cefquinome against E. coli was determined as 8 μg/ml at the dose of 75 mg/udder. The derived ECOFF, COPD, together with ex vivo PK/PD-based population dose prediction served as important steps in the establishment of optimum dose regimen and provided a useful interpretative criterion to categorize the antimicrobial susceptibility testing results of cefquinome.

The Role of PK/PD Analysis in the Development and Evaluation of Antimicrobials

Pharmacokinetic/pharmacodynamic (PK/PD) analysis has proved to be very useful to establish rational dosage regimens of antimicrobial agents in human and veterinary medicine. Actually, PK/PD studies are included in the European Medicines Agency (EMA) guidelines for the evaluation of medicinal products. The PK/PD approach implies the use of in vitro, ex vivo, and in vivo models, as well as mathematical models to describe the relationship between the kinetics and the dynamic to determine the optimal dosing regimens of antimicrobials, but also to establish susceptibility breakpoints, and prevention of resistance. The final goal is to optimize therapy in order to maximize efficacy and minimize side effects and emergence of resistance. In this review, we revise the PK/PD principles and the models to investigate the relationship between the PK and the PD of antibiotics. Additionally, we highlight the outstanding role of the PK/PD analysis at different levels, from the development and evaluation of new antibiotics to the optimization of the dosage regimens of currently available drugs, both for human and animal use.