Stability and compatibility of cimetidine hydrochloride and aminophylline in dextrose 5% in water injection

A controlled study was conducted to assess the physical compatibility of cimetidine hydrochloride (HCl) and aminophylline and the chemical stability of an admixture of the two medications in dextrose 5% in water (D5W) injection, over 48 hours at room temperature. Three one-liter admixtures were prepared, each containing cimetidine HCl 1200 mg and aminophylline 500 mg in D5W. One liter of only cimetidine HCl 1200 mg in D5W and one liter of only aminophylline 500 mg in D5W served as controls. Samples drawn from the five admixtures and immediately frozen were analyzed for cimetidine and theophylline content at times 0, 1, 6, 24, and 48 hours using high-performance liquid chromatography. Chemical stability of each drug was assessed relative to its time-zero concentration. Samples were also drawn from each test and control solution at every time interval to assess the pH. Admixtures were stored at room temperature out of direct sunlight for the duration of the study, and were visually inspected for color change, turbidity, cloudiness, and precipitation. Recovery of cimetidine and theophylline at all test intervals, pH assessments, and visual inspections of the admixtures showed that cimetidine HCl and aminophylline are both chemically stable and physically compatible for 48 hours at room temperature in one liter of D5W.