Drug interactions during anticonvulsant therapy in childhood: diphenylhydantoin, primidone, phenobarbitone, clonazepam, nitrazepam, carbamazepin and dipropylacetate.

It is well known that the concomitant use of different drugs may alter the reactions of the body towards the individual components. This is particularly important in long-term anticonvulsant therapy which is frequently a combined therapy. By carrying out statistical analysis of more than 6000 assays of the serum levels of antiepileptic drugs an attempt was made to gain insight into the possible drug interactions. The following results were obtained: 1. There was an increase in serum levels of diphenylhydantoin when either clonazepam or dipropylacetate (short-term therapy) was given concomitantly. 2. There was a decrease in serum levels of diphenylhydantoin when carbamazepine, primidone or dipropylacetate (long-term therapy) were administered concomitantly. 3. There was an increase in the serum level of phenobarbitone when it was administered together with diphenylhydantoin. 4. There was an increase in the serum level of primidone when it was administered together with clonazepam. 5. There was a decrease in the serum level of primidone if it was administered concomitantly with either carbamazepine or dipropylacetate (long-term therapy).