Endometrial tissue concentrations of ceftiofur derivatives following intrauterine infusion in both non-infected mares and mares with experimentally induced endometritis

Abstract

Intrauterine infusion of antimicrobials is common practice for the treatment of bacterial
endometritis, however evidence based guidelines are lacking. The objective of this study was to
determine endometrial concentrations of ceftiofur derivatives following intrauterine infusion in noninfected
mares and those with experimentally induced endometritis. It was hypothesized that endometrial
tissue concentrations of desfuroylceftiofur-acetamide (DCA; active metabolite of ceftiofur) would remain
above the minimum inhibitory concentration (MIC) for common uterine pathogens for greater than 24 h
in both groups of mares. Endometrial biopsy samples were collected from six mares during estrus
immediately prior to intrauterine infusion of 1g ceftiofur and at 4, 8, 12, 24, 36 and 48 h after infusion.
Desfuroylceftiofur-acetamide levels in endometrial tissue were measured using liquid chromatographymass
spectrometry (LC-MS) at each time point. Six further mares were then chosen that had been shown
to be susceptible to breeding induced endometritis. Once in estrus they were inoculated with 107 colonyforming
units (CFU) of Streptococcus equi zooepidemicus (S. zooepidemicus). 24 h following inoculation,
1g of ceftiofur was infused into the uterus and endometrial biopsies taken immediately prior to and at 6,
12, 24, 48, 72 and 96 h after infusion to determine tissue concentrations of DCA. In non-infected mares,
concentrations of DCA were above MIC90 for S. zooepidemicus and Escherichia coli (E. coli) for the 48
h-testing period. In mares with experimentally induced endometritis, concentrations of DCA were only
above MIC90 for E. coli for 6 h and S. zooepidemicus for 24 h.