Endometrial tissue and blood plasma concentration of ceftiofur and metabolites following intramuscular administration of ceftiofur crystalline free acid to mares.

This study investigates the effectiveness of ceftiofur crystalline free acid (CCFA) in treating infectious endometritis in mares, a condition often caused by a bacterium called Streptococcus equi ssp. zooepidemicus. The researchers tested whether an intramuscular injection of CCFA could maintain therapeutic levels in the horse’s endometrial tissue and blood plasma, finding that it does so for up to 25 days and should thus be a suitable treatment.

Objective and Methods

• The primary objective of this study was to ascertain if intramuscular (i.m.) administration of CCFA could exceed the minimum inhibitory concentration (MIC) of Streptococcus equi ssp. zooepidemicus in a horse’s endometrium, both after a single dose and multiple doses.
• For the experiment, the researchers used nine mares divided into three groups. The first group, consisting of three mares, was given a single i.m. dose of CCFA and monitored for 144 hours. Tissue biopsies and blood samples were collected at pre-designated intervals.
• The remaining two groups, each consisting of three mares, were given CCFA on days 0, 4, 11, and 18, and samples were collected over 25 or 49 days respectively.
• The blood and tissue samples were analysed using high-pressure liquid chromatography with tandem mass spectrometry to evaluate the concentration of desfuroylceftiofur acetamide, a direct measure of all ceftofur and ceftiofur metabolites in the sample.

Results

• Analysis revealed that the average concentration of desfuroylceftiofur acetamide in the blood plasma was 0.367 ± 0.0162 μg/ml at 96 hours post-administration.
• The average concentration in endometrial tissue was slightly higher at 0.510 ± 0.0418 μg/g at 96 hours and exceeded the MIC for Streptococcus equi ssp. zooepidemicus (0.25 μg/ml) for the entire 144-hour monitoring period in Group 1.
• Mares in Groups 2 and 3, which were given multiple doses of CCFA, maintained effective plasma concentrations for 25 days.
• Similarly, concentrations in the endometrial tissue remained above the MIC at most collection points for 25 days in these two groups.

Conclusions

• The study concluded that CCFA can maintain an effective concentration in a mare’s endometrial tissue for treating infections caused by Streptococcus equi ssp. zooepidemicus.
• Therefore, CCFA appears to be a promising method for the treatment of equine bacterial endometritis caused by this bacterium and other similar pathogens.