In Vivo PK/PD Relationship Of Cefquinome Against Streptococcus Agalectiae In Mice Mastitis Model

Streptococcus agalactiae is one of the most common pathogens causing mastitis in dairy cows,which has seriously hindered the development of dairy farming worldwide.Cefquinome is forth generation cephalosporins antibiotic for animals use exclusively.It has high effectiveness in the treatment of respiratory diseases and dairy mastitis.PK/PD model is a pharmacological research method which combines pharmacokinetics with pharmacodynamics.It can effectively show the relationship between dosage and response of drugs and provide scientific basis for the treatment of certain diseases.Compared with previous durg titirtion studies,it is more convincing and can reflect the relationship between drug concentration and antimicrobial efficacy in real time.This model is considered to be the dawn of pharmacological research.In this study,the PK/PD model that cefquinome against streptococcus agalactiae mice mastitis was established to evaluate the relationship between dosage and the effectiveness,to find the most appropriate PK/PD parameter and to calculate the corresponding values.Based on the calculation,the goal of this study was to provide the precise pharmacodyanmics targets for the different antibacterial efficacy.Those values will provide a certain theoretical basis for clinical use.The MIC and MBC detection were conducted in the mice plasma and MH broth adding 5% calf serum according to the micro broth dilution method guideline of CLSI.The results showed that MIC was 0.03 μg/m L,MBC was 0.06 μg/m L and MPC was 0.24 μg/m L.In vitro killing curve,for the experiment group started with 106 CFU/m L density,cefquinome concentration of 4×MIC and above could make 3~4log10 CFU/m L reduction of bacterial density.For the experimental group started with 107 CFU/m L density,cefquinome concentration of 4×MIC and above could cause 1~2log10 CFU/m L reduction of bacterial density.The antimicrobial effect of low bacterial concentration group was significantly higher than that of high bacterial concentration group(p<0.05).Cefquinome showed time-dependent drug characteristic in two vitro killing curves.The bacterial fluid was injected to the mammary gland of mice.After 9 h,bacterial colonization in the mammary gland of mice met the requirements of mastitis model.Single intramammary gland administration of cefquinome was done to against S.agalactiae-induced mice mastitis model including 30 μg/gland,60 μg/gland,120 μg/gland and 240 μg/gland respectively.And these administration groups were set as the experimental groups.After the administration,the mammary gland was collected and homogenized for the visible counting to show the effectiveness.The results showed that compared with the 30 μg/gland and 60 μg/gland groups,the dosages of 120 μg/gland and 240 μg/gland could significantly reduce the concentration of bacteria,the decrease number was approximately at the 2~3log10 CFU/gland value(p<0.05).The antibacterial effect of cefquinome on mammary gland of mice showed time-dependent drug characteristic.In the mean time,the plasma of mice was collected to analyze the concentration of cefquinome by HPLC-MS/MS.The data was analyzed using the One-compartment absorption model of the Winnonlin software 5.2.1.The key pk parameters were T1/2α(0.07±0.005 h),T1/2β(0.49±0.083h),Tmax(0.21±0.02h),MRT(0.95±0.128 h)and Vss(0.23±0.041 L/kg).The PK/PD model was constructed by combing the pharmacokinetic data with the vivo pharmacodynamics data.The best appropriate PK/PD parameter was %f T>MIC,the correlation coefficient was 0.9863,and the second appropriate was f AUC/MIC,the correlation coefficient was 0.9582,and the lowest was f Cmax/MIC,the correlation coefficient was 0.8774.The new PK/PD parameters constructed by replacing MIC with MPC were fitted with pharmacodynamics,%f T>MPC,the correlation coefficient was 0.9917,f AUC/MPC,the correlation coefficient was 0.9817,and f Cmax/MPC,the correlation coefficient was 0.9517.When inhibited the growth of bacteria in vivo,the pharmacodyanmics target value of %f T>MIC was 31%,%f T>MPC was 8.1%.When the concentration of bacteria decreased by 1log10 CFU/gland,the pharmacodyanmics target value of %f T>MIC was 47%,%f T>MPC was 9.8%.When the concentration of bacteria decreased by 2log10 CFU/gland,the pharmacodyanmics target value of f T>MIC was 81%,%f T>MPC was 24.5%.The PK/PD targets values for different antimicrobial effects of cefquinome in the mice mastitis model of Streptococcus agalactiae were obtained,which provided a basis for rational drug use in clinic.