Compatibility and stability of cefazolin sodium, clindamycin phosphate, and gentamicin sulfate in two intravenous solutions

We studied the compatibility and stability of clindamycin phosphate admixed with gentamicin sulfate and cefazolin sodium in small-volume diluents under specific storage conditions. In two replicate 100 ml dilutions of NaCl 0.9% injection and dextrose 5% (D5W) injection, clindamycin phosphate 900 mg was admixed with gentamicin sulfate 80 mg and cefazolin sodium 1 g. Drug concentrations were determined at the time of preparation and at 1, 4, 8, 12, 24, and 48 hours. Clindamycin and cefazolin were assayed by high-performance liquid chromatography and gentamicin was assayed by fluorescence polarization immunoassay. Visual inspections and pH determinations of each solution were performed at each assay time. Test solutions were maintained at constant room temperature and fluorescent lighting. Concentrations of clindamycin and gentamicin remained greater than 90 percent of the original concentrations throughout the study. Cefazolin concentrations dropped below 90 percent in D5W injection at 4 hours after admixture and at 12 hours after admixture in NaCl 0.9% injection. Visual analyses and pH changes revealed no significant changes. The combination of clindamycin phosphate 900 mg, gentamicin sulfate 80 mg, and cefazolin sodium 1 g in D5W 100 ml was found to be compatible for up to 4 hours. The duration of compatibility for these three drugs in 100 ml of NaCl 0.9% was 12 hours.