Emergency phenytoin loading by constant intravenous infusion

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We evaluated the efficacy of constant intravenous (IV) phenytoin infusion. Thirty-eight patients were evaluated prospectively for complications of continuous-infusion phenytoin loading. A total dose of 18 mg/kg was administered as a solution of 500 mg phenytoin in 50 mL normal saline using a constant infusion pump. The initial delivery rate was 40 mg/min. Cardiac rhythm was monitored by telemetry, and rhythm strips and vital signs were obtained every 15 minutes during infusion. Therapeutic phenytoin blood levels (greater than 10 micrograms/mL) were achieved in 37 patients (97%). Infusion was discontinued in one patient because of IV site irritation shortly after initiation of the infusion. Phenytoin levels in the toxic range were seen immediately postinfusion in 22 patients and in the four-hour postinfusion samples of 16 patients. Thirteen of 18 levels drawn 12 to 24 hours after infusion were therapeutic. Phenytoin levels greater than 20 micrograms/mL were tolerated without significant change in rhythm, QRS interval, or QT interval. A small statistically significant (P less than .05) decrease in systolic and mean arterial pressure was noted during the infusion. Complications included burning at the IV infusion site in four patients; the discomfort was relieved in three cases by reducing the rate of infusion to 20 mg/min. Seizures occurred in two patients during the infusion, requiring the additional use of diazepam or phenobarbital. Administration of a loading phenytoin dose by constant IV infusion is an effective means for achieving therapeutic levels quickly.