Serum levels of phenytoin and phenobarbital in epileptic patients treated with mixture antiepileptic tablets, Comital-L or Hydantol-F.

Serum levels of both phenytoin and phenobarbital were determined by homogenous enzyme immunoassay in 59 epileptic patients treated chronically with either Comital-L or Hydantol-F tablets. The majority of the patients receiving Comital-L tablets showed low serum levels of phenytoin and high serum levels of phenobarbital, while patients treated with the usual daily dosage of Hydantol-F tablets showed adequate therapeutic serum levels of both phenytoin and phenobarbital. From the results obtained, the dose ratio of phenobarbital to phenytoin in Comital-L tablet seemed inappropriate to obtain adequate therapeutic serum levels of both drugs simultaneously. Since the dosage of each anticonvulsant drug used concurrently should be established individually, the use of such fixed-dosage mixture tablets of antiepileptic drugs as Comital-L or Hydantol-F in daily clinical practice should be reconsidered from the viewpoint of serum level monitoring of antiepileptic drugs.