In vitro evaluation of nasogastric administration methods for phenytoin

The effect on phenytoin recovery of various methods of nasogastric administration of phenytoin suspension was studied. Phenytoin acid suspension 4 mL (100 mg) was administered through a nasogastric (NG) tube using 10 methods designed to simulate clinical situations. The suspension was given either undiluted or diluted, with or without irrigation of the NG tube. Solutions of 5% dextrose injection, 0.9% sodium chloride injection, sterile water for irrigation, and lactated Ringer's injection were used as diluents or irrigants. After each administration, 40 mL of air was forced through the NG tube to expel any remaining suspension. Phenytoin concentration was assayed by high-performance liquid chromatography before and after administration through the NG tube. In the method that used no diluent or irrigation, 75.5 +/- 5.3% of the initial dose volume was lost, significantly more loss than with any of the other methods. The mean dose volume lost for all of the other nine methods was 6.4 +/- 3.4%. The type of fluid used for dilution or irrigation had little influence on phenytoin recovery. Until other methods can be evaluated, phenytoin suspension should be diluted and irrigated with at least 20 mL of fluid when given by nasogastric tube. Evacuation of the tube with 40 mL of air after phenytoin administration is also recommended.