Oral and intramuscular phenytoin.

Twelve epileptic patients, after 1 wk on their previously established oral dose of phenytoin, were given a 50% larger dose intramuscularly for 1 wk after which they were put on an oral phenytoin regimen for 1 wk on a dose one-half the original oral dose. Plasma phenytoin levels did not show a sharp decrease in the intramuscular (im) nor a dangerous increase in the second oral phase. Those receiving drug once a day maintained remarkably stable levels. By the end of the im phase, patients receiving drug in multiple daily doses had some increase in plasma levels proportional to the dose increase. Seizure control was maintained equally well throughout all phases of the study. Except for local irritation at the site of injection, there were no adverse experiences. The data indicate that the dosage regimen described is suitable for patients on oral phenytoin who have to be transferred to im drug for short periods.