Phenytoin monotherapy for epilepsy: a long-term prospective study, assisted by serum level monitoring, in previously untreated patients.

Of 31 previously untreated patients with grand mal and/or partial seizures referred to a neurological clinic and treated with phenytoin monotherapy, assisted by serum level monitoring, 26 have been followed up for a mean of 42 months. Seizures were completely controlled in 80%. Failure of optimum phenytoin monotherapy occurred in 12%. The degree of seizure control was significantly related to phenytoin serum levels. The success of monotherapy was probably related to availability of serum level monitoring and to the study of a previously untreated population with a relatively short history of epilepsy. The main reasons for failure of monotherapy were poor compliance and the presence of additional neuropsychiatric handicaps, which commonly occur together. The place for polytherapy in the event of failure of monotherapy has still to be defined.