Daily oral phenobarbital reduces the frequency of recurrences, but has a high incidence of behavioral and cognitive side effects.
Furthermore, in a placebo-controlled study of children with FS, the mean IQ of those who had received daily phenobarbital was 7 points lower than controls after 2 years and 5 points lower after the medication had been discontinued.
Daily oral valproic acid is also effective in reducing the frequency of recurrent FS but the high incidence of fatal liver failure in infants and young children 30 suggests that the risks of this drug outweigh the benefits in this situation.
Daily carbamazepine and phenytoin are not effective in preventing recurrences.