Stability of intravenous admixtures containing aztreonam and cefazolin.

The stability of aztreonam and cefazolin in intravenous admixtures was studied. Each of the following combinations of drugs was added to both 5% dextrose injection and 0.9% sodium chloride injection in polyvinyl chloride containers: aztreonam 20 mg/mL and cefazolin 20 mg/mL (as the sodium salt); aztreonam 10 mg/mL and cefazolin 5 mg/mL; aztreonam 20 mg/mL and cefazolin 5 mg/mL; and aztreonam 10 mg/mL and cefazolin 20 mg/mL. One of each of these admixtures was stored at 23-25 degrees C for 48 hours and at 4-5 degrees C for seven days. At various storage times the admixtures were inspected for visual changes, and 1-mL samples were tested for pH and assayed using a stability-indicating high-performance liquid chromatographic assay. No visual changes were observed, and changes in pH were negligible. Concentrations of aztreonam and cefazolin under both storage conditions decreased by less than 3%. Intravenous admixtures of aztreonam and cefazolin at the concentrations studied are stable for at least 48 hours at 23-25 degrees C and for seven days at 4-5 degrees C.