Stability of Antibiotic Admixtures Frozen in Minibags

This study investigated the stability of frozen antibiotic admixtures prepared in minibags containing 50 ml of 0.9 percent normal saline and 5 percent dextrose in water. The minibag antibiotic admixtures studied were ampicillin sodium 1 g, carbenicillin disodium 2 g, cephalothin sodium 1 g, cloxacillin sodium 1 g, cefazolin sodium 1 g, gentamicin sulfate 50 mg, penicillin G potassium 2 million units, erythromycin gluceptate 500 mg and rolitetracycline base 275 mg. The stability of each antibiotic was determined by a quantitative microbiological agar gel diffusion assay. The minibags were frozen within an hour of the admixtures being prepared. During storage in a freezer at −20 °C (–4 °F), the minibags were placed in a storage module to reduce unnecessary handling. Assays were conducted on minibags which had been frozen for 24 hours, 7 days and 30 days. All thawed samples were re-assayed after storage at 5–6 °C (21–23 °F) for 21 hours. The results of the study indicated that minibag admixtures of carbenicillin disodium, cephalothin sodium, cloxacillin sodium, gentamicin sulfate, penicillin G potassium, erythromycin gluceptate, cefazolin sodium and rolitetracycline base in the concentrations tested can be frozen for 30 days without a significant loss in activity. These antibiotics were also stable when thawed and stored at 5–6 °C (21–23 °F) for 21 hours. Ampicillin sodium admixtures were not stable when frozen. A handling procedure for the frozen minibags is described. Specific recommendations are also included for freezing and thawing the minibags and in the use of a specially designed storage module.