Investigation of the Crystallization of Phenytoin in Normal Saline

Abstract
A study was designed to determine if the admixture of phenytoin in normal saline would remain physically stable for a suitable period of time to allow for intravenous infusion. Five phenytoin concentrations (1.0 mg/ml, 2.5 mg/ml, 5.0 mg/ml, 7.5 mg/ml, and 10.0 mg/ml) were prepared in triplicate by adding a sufficient volume of normal saline to the appropriate volume of phenytoin sodium injection to produce a total volume of 100 ml. Aliquots of all solutions were withdrawn at zero, 1, 8, 16, and 24 hours. Solutions were filtered through a 0.22 micron millipore filter and the concentration of phenytoin and pH of each solution was determined. A significant concentration difference was not seen between zero time and 24 hours. The pH of the samples ranged from 9.75 to 11.00. While phenytoin sodium appears to be stable in the concentrations tested when sodium chloride 0.9% is the vehicle, several important factors must be considered and caution must be used if the admixture is administered intravenously.

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