Plasma antiepileptic drug monitoring in a neurological practice: a 25-year experience.

Rates for being free of all epileptic seizures for at least 1 year and for ceasing therapy after 3-5 years of full seizure control were similar in 548 treated epileptic patients referred from 1962 to 1970, during which period plasma antiepileptic drug concentration monitoring became available (32.7 and 17.0%, respectively), in 960 patients referred from 1971 to 1979, when such monitoring was used increasingly (29.6 and 14.9%, respectively), and in 348 patients referred from 1980 to 1989, when this monitoring was widely available (30.5 and 10.1%, respectively). However, monitoring was associated with higher rates of full seizure control in patients seen within 6 months of their first seizure, even when patients with only a solitary seizure were excluded. Possibly, monitoring then helped achieve early complete suppression of not yet established seizure processes, but had less effect on already entrenched seizure mechanisms. Plotting cumulative percentages of patients with fully controlled seizures versus plasma antiepileptic drug concentrations yielded data that were broadly in keeping with conventional 'therapeutic' ranges for phenytoin, carbamazepine, phenobarbital, and ethosuximide monotherapy. With a given plasma phenobarbital (but not phenytoin or carbamazepine) concentration, rates of full seizure control were appreciably higher for generalized onset than for partial onset seizures. Use of a second antiepileptic drug was associated with improved full seizure control in both generalized onset and partial onset seizures, which had not been controlled by monotherapy; adding a third drug yielded little further benefit.