Milk Disposition Kinetics, Residue and Efficacy of Rifaximin After Intramammary Administration in Lactating Cow

<b>Background:</b> Rifaximin is a non-aminoglycoside antibiotic utilized for the treatment of mastitis in cows, but its milk disposition kinetics, residue, and bacteriological status in lactating cow milk have hardly been reported. This study aimed to assess the milk disposition kinetics and residue of rifaximin in milk and to evaluate the bacteriological status in milk after intramammary treatment with rifaximin. <b>Methods:</b> An ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) approach was developed to assess rifaximin concentrations in milk. Milk disposition kinetics parameters of rifaximin in cow milk were obtained by non-compartment model analysis. Rifaximin residues in milk were analyzed up to 108 h post-administration to estimate the withdrawal period. Clinically, the efficacy of Rifaximin Intramammary Infusion (Lactating Cow) was evaluated in mastitis cases caused by various pathogens and compared with lincomycin as the control drug, including clinical cure rate, bacteriological cure rate, and somatic cell count (SCC) at D21 post-treatment. <b>Results:</b> The C_max of rifaximin in milk was 54,273.3 ± 12,421.32 ng/mL, the area under the curve (AUC) was 340,731.8 ± 43,968.82 h⋅ng/mL, the T_1/2 was 5.57 ± 0.68 h, the mean resident time (MRT) was 7.3927 ± 1.34 h, and the area under the moment curve (AUMC) was 2,475,745 ± 230,305.1 h⋅h⋅ng/mL. Based on rifaximin residues in milk, the withdrawal period for cow milk was calculated to be 95.1 h. Clinically, Rifaximin Intramammary Infusion (Lactating Cow) demonstrated a clinical cure rate of 83.33% and a bacteriological cure rate of 76.67% in mastitis cases caused by various pathogens, with both rates being 10% higher than those of lincomycin. At D21 post-treatment, the rifaximin group had a significantly lower SCC than the lincomycin group (<i>p</i> < 0.05). <b>Conclusions:</b> Rifaximin exhibits favorable milk disposition kinetics, an acceptable withdrawal period of 95.1 h, and good clinical and bacteriological cure rates in bovine mastitis. These findings support rifaximin as a useful intramammary option and contribute to rational antimicrobial use and milk safety in dairy.