Abstract
The stability and compatibility of clindamycin phosphate with three aminoglycosides, amikacin sulfate, tobramycin sulfate, and gentamicin sulfate, admixed in either glass bottles or plastic bags, were studied under various storage conditions. In addition to the various two-drug combinations, each antibiotic was studied alone in the same solutions under the same storage conditions investigated for the various combinations. Clindamycin phosphate was admixed with amikacin sulfate in 100 ml glass bottles of both dextrose 5% in water (D5W) and NaCl 0.9%. The resultant solutions were examined for visual clarity; both pH and antibiotic concentrations were measured at the time of mixing and at 1, 4, 8, 12, 24, and 48 hours later. The solutions were maintained at room temperature under ambient lighting conditions throughout the observation period. Clindamycin phosphate was also admixed with tobramycin sulfate and gentamicin sulfate, in separate experiments, in 50 ml plastic bags of D5W and NaCl 0.9%. These solutions were examined, at the time of mixing, for visual clarity, pH, and antibiotic concentration and then frozen at −20°C. They were thawed 14 and 28 days later and reexamined. Clindamycin phosphate concentrations were measured by high performance liquid chromatography; those of the aminoglycosides were determined by a fluorescence polarization immunoassay. A working definition of significant instability or incompatibility was defined as a greater than 10 percent loss of original antibiotic concentration. All single antibiotic solutions were stable throughout the observation periods. The clindamycin phosphate-amikacin sulfate combination was stable for 48 hours. While most frozen solutions were stable for 28 days, the tobramycin sulfate-clindamycin phosphate solution was only stable for 14 days, with the tobramycin sulfate concentration decreasing by 16.6 percent from its original concentration at 28 days.
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