Acute effects of intravenous phenytoin on the frequency of inter-ictal spikes in man.

Phenytoin was administered intravenously to six adult epileptic patients in doses ranging from 500--1000 mg (equivalent to 5.6 mg/kg--20 mg/kg body weight). A significant decrease in the frequency of inter-ictal spikes in the EEG was seen and this effect was most marked 10--20 min after the infusion, when the mean spike count was reduced to 27% (s.d. 17%) of the control (P less than 0.05). In one subject the decrease in inter-ictal spikes coincided with a decrease in fit frequency. Adverse reactions affecting the vestibular system occurred in three patients at doses of 15--20 mg/kg. No cardiovascular complications were observed in any subject. The overall results suggest that doses of 7.5--10 mg/kg would be sufficient to significantly reduce the frequency of inter-ictal spikes in the EEG.