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Stability of Fosphenytoin Sodium with Intravenous Solutions in Glass Bottles, Polyvinyl Chloride Bags, and Polypropylene Syringes

OBJECTIVE: To determine the stability of fosphenytoin sodium admixtures with NaCl 0.9% injection and dextrose 5% (D5W) injection when stored in glass or polyvinyl chloride (PVC) containers, to evaluate the compatibility of fosphenytoin with 11 other intravenous solutions, and to determine the stability of fosphenytoin repackaged in polypropylene syringes. METHODS: Dilutions of fosphenytoin sodium 1, 8, and 20 mg phenytoin sodium equivalents (PE)/mL were prepared in NaCl 0.9%, D5W, and 11 other intravenous fluids. Aliquots of each solution in NaCL 0.9% or D5W were transferred to three glass bottles for storage at 25 °C and 21 PVC bags for storage at 25, 4, or −20 °C Aliquots of each admixture with the other intravenous fluids were transferred to three PVC bags and stored at 25 °C for 7 days. In addition, 63 syringes were filled with fosphenytoin sodium 50 mg PE/mL (undiluted) and stored at 25, 4, or −20 °C. Samples of each solution from the three containers were analyzed for visual compatibility, pH, and fosphenytoin concentration initially and at 0.5, 1, 2, 3, 7, 14, and 30 days during storage at 25 and 4 °C and at 1, 7, 14, and 30 days during storage at–20 °C. Following removal of containers from the freezer, additional samples were obtained after 7 days at 4 or 25 °C, and 7 days at 25 °C, and then 7 days at −20 °C. RESULTS: No visible precipitation or change in color or clarity was observed in any of the fosphenytoin solutions during the study. The concentration of fosphenytoin at each sampling time remained within 97–104% of initial concentration, regardless of container, concentration, intravenous admixture, or storage temperature. CONCLUSIONS: Fosphenytoin sodium, either undiluted in polypropylene syringes or diluted with NaCl 0.9% or D5W in PVC bags, remains stable for at least 30 days at room temperature, under refrigeration, or frozen. After removal from the freezer, fosphenytoin can be thawed, kept at 4 or 25 °C for 7 days, and then returned to the freezer for another 7 days. Admixtures of fosphenytoin sodium in various other intravenous fluids are stable for at least 7 days at room temperature.