EquineReview: September–October 2023

The objective of this study was to measure the concentration of gentamicin and penicillin in the uterine fluid of mares following intrauterine infusion of either a standard (PPGent) or long-acting (LA-PPGent) compounded formulation of procaine penicillin and gentamicin. Ten reproductively sound mares in early estrus were administered 2378 mg of procaine penicillin and 200 mg of gentamicin via a single intrauterine infusion in either a standard (n=5) or slow-release (n=5) formulation. Penicillin and gentamicin concentrations were assessed by inserting a pre-weighed length of absorbent umbilical tape into the uterine lumen using a double guarded pipette; analyses were then performed using chromatography and mass spectrometry. Mean intrauterine drug concentrations of PPGent peaked at 0.5 hours (penicillin: 10 123.0 ± 4298.0 µg/ml; gentamicin: 3397.3 ± 1338.5 µg/ml) and exceeded the minimum inhibitory concentration for relevant organisms for 72 hours (penicillin: 2.59 ± 6.34 µg/ml; gentamicin: 2.14 ± 2.4 µg/ml). Mean concentrations of LA-PPG were lower at peak and exceeded the minimum inhibitory concentration for 24 hours for penicillin and 32 hours for gentamicin. These results support the combined use of procaine penicillin and gentamicin as an intrauterine therapy in the treatment of endometritis caused by susceptible organisms. It is important to note that this was a compounded formulation, and it cannot be assumed that the combination of commercially available preparations in practice will have the same result nor be clinically efficacious. However, this is interesting and clinically relevant research, and the author looks forward to further research from this group.