Stability of cephapirin sodium admixtures after freezing and conventional or microwave thaw techniques

The freeze-microwave thaw technique has important advantages compared with conventional piggyback delivery systems. A requirement for the implementation of this technique, however, is the documentation of antibiotic stability following freezing and microwave thawing. The purpose of this study was to assess the stability of a commonly used cephalosporin, cephapirin sodium, following freezing and conventional or microwave thawing. This data was not previously available. Cephapirin sodium was admixed with either 5% dextrose injection or 0.9% sodium chloride injection in polyvinylchloride minibags at concentrations of 10 and 40 mg/ml and then frozen for 14 days. Admixtures were then thawed conventionally or by microwave heating. Cephapirin concentrations were determined spectrophotometrically after reconstitution, immediately after thawing, and 6, 12, and 24 hours after thawing. No significant differences in admixture potency after reconstitution, immediately after thawing, or at 6, 12, and 24 hours after thawing were observed when thaw techniques were compared. All admixtures retained at least 90% of labeled content regardless of thaw technique, type of diluent, or initial concentration. In addition, all admixtures retained at least 90% potency 24 hours after thawing when compared with the actual concentration determined immediately after reconstitution. The rate of cephapirin degradation was not influenced by thaw technique, type of diluent, or initial admixture concentration. The results of this study suggest that cephapirin sodium may be added to the list of drugs capable of withstanding freeze-microwave thaw treatment.