SUMMARY
Cefuroxime sodium (Zinacef®) is a new semisynthetic, broad spectrum cephalosporin antibiotic for parenteral administration which is stable to most of the β‐lactamases.
The stability of cefuroxime sodium in aqueous solutions, with or without phosphate buffer, and in 5% dextrose and 0.9% sodium chloride injections was studied using a stability‐indicating high‐pressure liquid chromatographic method developed in our laboratory. The optimum pH range of stability was determined to be ˜ 4.5–7.3. Both buffered and unbuffered solutions followed first‐order decomposition. In 5% dextrose and 0.9% sodium chloride injections, cefuroxime was stable for 1 day (more than 90% potent) at 25°C and for at least 30 days at 5°C. At — 10°C, there was negligible decomposition after 30 days. The pH values of the solutions stored at 5°C and — 10°C remained in the maximum stability range and the solutions were clear even after 30 days of storage. Thawing the frozen solutions in a microwave oven adversely affected the stability.
A stability-indicating HPLC assay method has been developed to quantify metronidazole benzoate in suspensions. A study of the stabilities of two suspensions (16.0 mg/ml) of metronidazole benzoate in commercially available vehicles, Ora-Plus and a mixture of Ora-Plus and Ora-Sweet, showed that both suspensions were stable for at least 90 days at room temperature. The mobile phase required to elute metronidazole benzoate contained 40% acetonitrile versus approximately 10% for the free base. The solubility of the ester in water at 25 degrees C was found to be approximately 0.1 mg/ml versus 10 mg/ml for the free base. The ester did not hydrolyse significantly to the free base after storage for 8 h at 37 degrees C in simulated gastric fluid, and 5 h at 37 degrees C in simulated intestinal fluid. The bitter tasting metronidazole may not be satisfactorily substituted with its tasteless ester in the treatment of local gastrointestinal infections.
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