Decrease in Serum Diphenylhydantoin Levels after Withdrawal of Phenobarbital in Epileptics Treated with Both Drugs

Abstract

In six epileptic children who had been treated with diphenylhydantoin, phenobarbital, and/or mysoline, a decrease in serum diphenylydantoin levels was found in five cases on the 23 rd to 35 th day of withdrawal of phenobarbital and mysoline, among which four cases might be explained by enhanced activity of drug metabolizing enzymes which were persisting even after withdrawal of phenobarbital, and one case might be due to elimination of inhibitory action of phenobarbital upon diphenylhydantoin metabolism