title: Stability of aqueous solutions of amoxicillin sodium in the frozen and liquid states.
abstract: The stability of aqueous admixtures of amoxicillin sodium in both the liquid and frozen (solid) states was studied. Admixtures of amoxicillin sodium were prepared in sterile water for injection to a theoretical concentration of 10 mg/mL. For each experimental run, 2-mL aliquots of the admixture were placed in stoppered glass volumetric flasks and stored at temperatures ranging from 19.5 degrees C to -30 degrees C; 16 flasks were stored at each temperature. After equilibration for approximately 20 minutes, duplicate flasks at each temperature were removed from storage conditions for time-zero assay. Subsequently, duplicate flasks were assayed at various times, depending on the storage temperature, for up to 13 days or until more than 80% of the drug had degraded. All samples were assayed at least in duplicate using high-performance liquid chromatography. When amoxicillin solutions were in the liquid state (at temperatures between 19.5 and 0 degrees C), the time required for the amoxicillin concentration to decrease to 90% of its initial value (t90) increased as temperature decreased. However, between 0 degree C and -7 degrees C, the t90 of frozen solutions decreased from two days to 1.08 hours. As temperature declined further, the rate of degradation decreased until the solution was completely frozen; at -30 degrees C, the t90 had increased to 13 days. Amoxicillin sodium is unstable in aqueous solutions stored between 0 degrees C and -20 degrees C. If admixtures of this drug are to be frozen for later use, the storage temperature should be below -30 degrees C.
mesh_terms: D000658:Amoxicillin; D002851:Chromatography, High Pressure Liquid; D004355:Drug Stability; D005612:Freeze Drying; D005615:Freezing; D006863:Hydrogen-Ion Concentration
chemical_list: D000658:Amoxicillin