# The Apparent pH Stability of Antibiotic Preparations Used for Uterine Infusions in Mares

## TL;DR

This study evaluates how pH stability of antibiotic uterine infusions in mares is affected by storage conditions and solution types.

## Contribution

The study provides new insights into how pH stability of antibiotic solutions for mares' uterine infusions is influenced by storage and formulation factors.

## Key findings

- Aminoglycoside antibiotics showed increased pH over time, suggesting buffering agents like sodium bicarbonate can improve stability.
- Other antibiotics exhibited decreased pH, especially at higher temperatures, potentially reducing their effectiveness.
- pH stability of uterine infusions is significantly influenced by storage conditions and vehicle solutions.

## Abstract

Endometritis is the primary cause of subfertility in mares. Treatment often involves ecbolics, antibiotics, and uterine lavage. Antibiotics may be administered systemically or directly infused into the uterus. Although many recommendations exist on preparing uterine infusions in mares, their effectiveness has not been thoroughly evaluated. This study aimed to assess in vitro the apparent stability of various preparation methods for antibiotic uterine infusions based on these recommendations. The most frequently used antibiotics in clinical practice were tested, and guidelines for field veterinarians were developed.

Infectious endometritis is a primary cause of subfertility in mares. Many manuals and guidelines are available for administering intrauterine infusions of antibiotics and biofilm-disrupting solutions, detailing concentrations, vehicle solutions, and buffers. However, the stability of these combinations has not been documented. Therefore, our study investigated how factors such as storage temperature, concentration, buffer types, combinations of biofilm disruptors, and vehicle solutions affected pH stability over 24 h in uterine infusion preparations commonly used by veterinary theriogenologists to treat endometritis in mares. In experiment 1, amikacin, ampicillin, ceftiofur, ciprofloxacin, gentamicin, penicillin G potassium, penicillin G procaine, and ticarcillin clavulanate were diluted in saline and lactated Ringer’ s solution and stored at 5 ° C, 21 ° C, and 37 ° C for 24 h. Solutions were evaluated for pH and physical characteristics at 0, 1, 3, 6, and 24 h after storage. In experiment 2, 1- and 2-g doses of amikacin, ampicillin, and gentamicin were compared, evaluating the same volume at different concentrations and their stability over 24 h. Experiment 3 combined biofilm chelators (i.e., Tris-EDTA, hydrogen peroxide, and dimethyl sulfoxide) with antibiotic solutions and evaluated interactions among products. Experiment 4 compared the stability of each antibiotic diluted in saline and lactated Ringer’ s solution. Statistical analysis was performed using GraphPad Prism 9.3.0. Significance was set at p < 0.05. The results indicated that the stability of antibiotic solutions for uterine infusions in mares is significantly influenced by storage conditions and pH fluctuations. Solutions containing aminoglycosides showed an increase in pH over time, suggesting that buffering agents like sodium bicarbonate can enhance stability. In contrast, other antibiotics exhibited a decrease in pH, particularly at elevated temperatures, which may reduce their effectiveness. In conclusion, the pH stability of uterine infusions is affected by various storage conditions and vehicles, underscoring the importance of evaluating antibiotic treatments for quality control. While pH changes were observed, the potential impact on the overall stability or antimicrobial activity of the solutions requires further investigation.