Stability of intravenous admixtures of aztreonam and ampicillin

The stability of aztreonam and ampicillin in intravenous admixtures containing both drugs was studied. Each of the following drugs and combinations of drugs was added to both 5% dextrose injection and 0.9% sodium chloride injection: aztreonam 10 and 20 mg/mL, ampicillin sodium 5 and 20 mg/mL, aztreonam 20 mg/mL and ampicillin sodium 20 mg/mL, aztreonam 20 mg/mL and ampicillin sodium 5 mg/mL, aztreonam 10 mg/mL and ampicillin sodium 20 mg/mL, and aztreonam 10 mg/mL and ampicillin sodium 5 mg/mL. One of each of these admixtures was stored at 25 degrees C for 48 hours and 4 degrees C for seven days. At various storage times the admixtures were inspected for visual changes and 2-mL samples were examined microscopically for crystalline and particulate matter, tested for pH, and assayed by high-performance liquid chromatography. No visual changes were observed. In the two-drug solutions, pH was influenced by concentrations of the two drugs and stability of the drugs was influenced by the solution pH. The pH of single-drug aztreonam admixtures did not change during storage, but the pH of single-drug and two-drug admixtures containing ampicillin decreased. In single-drug admixtures, aztreonam loss under both storage conditions was less than 10% but ampicillin loss was more than 10% in 0.9% sodium chloride injection and more than 50% in 5% dextrose injection. The stability of ampicillin was increased in the presence of aztreonam, and the stability of aztreonam was decreased in the presence of ampicillin.(ABSTRACT TRUNCATED AT 250 WORDS)