Impact of temperature and water hardness on the stability of mixed tetracyclines (chlortetracycline, oxytetracycline, and tetracycline) used in veterinary medicine.

Objective: This study examines how temperature and water hardness affect the stability of tetracycline (TC), oxytetracycline, and chlortetracycline (CTC) in a mixed solution using liquid chromatography-tandem mass spectrometry to simulate typical livestock treatment conditions.

Methods: Calibration curves (0.8 to 8 mg/L) and quality control spikes (1.33, 2.56, and 5.30 mg/L) were utilized to ensure accuracy. Reagent, soft, and hard waters were tested at 22 and 35 °C. The stability of 7 commercial TC products was then evaluated under the same conditions.

Results: Tetracycline and oxytetracycline exhibited stability across all conditions with consistent recoveries, regardless of water hardness or temperature. In reagent water, CTC was stable for 25 hours, but in soft and hard water, the recoveries diminished over time. Temperature further adversely affected CTC stability, with marked degradation at 35 °C. Upon validation, the stability of 7 commercial TC products was tested using the same conditions, mirroring the behavior of the neat standards. Notably, CTC-containing products like Chloronex and Pennchlor 64 showed similar degradation profiles, reinforcing the impact of water hardness and temperature on CTC stability.

Conclusions: The findings emphasize the significant influence of water hardness and temperature on CTC stability. Proper handling and storage practices for TC-based medications are essential to ensure control of CTC-containing products like Chloronex and Pennchlor 64.

Clinical relevance: This study underscores the importance of proper storage for CTC-based medications, as their stability is significantly affected by water hardness and temperature, impacting treatment efficacy in livestock.