Stability of Important Veterinary Antibiotics Amoxicillin, Sulfadiazine, and Trimethoprim in Practice-Relevant Model Solutions.

Due to the frequent use of veterinary drugs in animal husbandry, it is important to know their environmental behavior. In this context, little attention has been paid to the stability of the active ingredients in solutions prepared for administration. This is particularly problematic for antibiotics that trigger resistance when administered subtherapeutically. In order to investigate a possible influence of the preparation and storage of veterinary drugs on compound stability, three widely used antibiotics (amoxicillin, sulfadiazine, trimethoprim) were prepared in different model solutions. Depending on their individual stabilities, the incubation period lasted up to 70 days. Samples were analyzed at regular intervals by high-performance liquid chromatography-diode array detection and ultraviolet spectrophotometry. Following official recommendations, the investigations covered various parameters, e.g., pH, buffer substances, influence of light, and temperature. Sulfadiazine was incubated together with trimethoprim at concentrations of 120 mg L