A PK/PD model for the evaluation of clinical rifaximin dosage for the treatment of dairy cow mastitis induced by Escherichia coli

Abstract

Escherichia coli (E. coli) is an opportunistic pathogen that can cause clinical mastitis in dairy cows worldwide. Mastitis produces severe symptoms in dairy cows, such as udder inflammation, the production of harmful substances, reduced milk production, and altered milk quality. Intramammary injections of rifaximin have a beneficial effect on dairy cow mastitis, especially for mastitis caused by E. coli. However, we do not know whether the currently accepted clinical administration scheme is reasonable. Therefore, the purpose of this experiment was to evaluate the clinical dosing regimen for curing mastitis induced by E. coli. In this study, the pharmacokinetics of four single dose groups (50, 100, 200, and 400 µg/gland) were studied in CD-1 lactating mice, and the main pharmacokinetic parameters were obtained by non-compartment and two-compartment model of Phoenix 8.1 software. A total of 5,000 colony-forming units (CFU) of E. coli ATCC25922 were injected into the mammary glands of mice under anatomic microscope guidance. After 12 h of growth in vivo, the mouse mastitis model was successfully developed. In pharmacodynamics experiment, 12 different dosing regimens (doses ranged from 25 to 800 µg/gland and two dosing intervals of 12 and 24 h) were used to study the therapeutic potential of rifaximin for mastitis. The PK/PD model was established by integrating pharmacokinetics and pharmacodynamics using the inhibitory sigmoid E_max model. The optimal antibacterial effect was 2log₁₀CFU/gland reduction of bacterial colony counts in vivo, when the magnitude of AUC₂₄/MIC exceeded 57.80 h. A total of 57.80 h of AUC₂₄/MIC was defined as a target value in the Monte Carlo simulation. The clinically recommended dosage regimen of 100 mg/gland every 12 h in a day achieved a 91.08% cure rate for the treatment of bovine mastitis caused by E. coli infection.

Keywords: Escherichia coli; Mastitis; Monte Carlo simulation; PK/PD model; Rifaximin.

Fig. 1

In vitro time bactericidal curve of rifaximin against E. coli ATCC 25,922 with different initial bacterial load. A 10⁶ CFU/ml initial inoculum group. B 10⁷ CFU/ml initial inoculum group

Fig. 2

The curve of concentration vs time of rifaximin in CD-1 mouse mammary glands following intramammary administration doses of 50, 100, 200, and 400 µg/gland (n = 6)

Fig. 3

The effect of rifaximin on mastitis induced by E. coli in mouse after 12 dose regimens designed with 25, 50, 100, 200, 400, and 800 µg/gland and dosing intervals 12, and 24 h, which was expressed as ∆logl0CFU/gland

Fig. 4

The relationship between PK/PD parameters and bactericidal effect of rifaximin (∆log10CFU/gland) analyzed by the sigmoid model. The dots represented the antibacterial effect of rifaximin (E = final log10CFU/gland-initial logl0CFU/gland) and the line represented the predicted value of E

Fig. 5

The probability distribution of AUC/MIC for rifaximin using a 10,000-subject Monte Carlo analysis based on the measured PK parameters obtained following mammary gland injection at 100 mg/gland with 24-h (a and b), 12-h (c and d) and 8-h (e and f) dosing interval in dairy cows and E. coli MIC distribution in this study. The areas of blue columns represent the probability of target attainment (PTA) for the 2log10CFU/gland decrease and the 2.5log10CFU/gland decrease of E. coli