Therapeutic drug level monitoring in the management of epilepsy.

A selected group of poorly controlled epileptic patients had their drug plasma concentrations measured. Of those on a single drug, 33% were noncompliant, 33% had drug concentrations in the subtherapeutic or toxic ranges and 34% had levels in the therapeutic range, 86% of which were in the low therapeutic range. In only 9% of the group on multiple drugs were both drug levels in the therapeutic range. Twenty-two per cent of patients were non-compliant for both drugs. Patients were followed up over 12 months with drug level monitoring and dosage adjustments; 49% were seizure-free and 36% had a reduction in seizure frequency of at least 50% over an 8-month period. All but 3.9% were put on a single-drug regimen, and 15.6%, which matched well with the number of non-compliant patients, had no change in seizure frequency. Therapeutic drug level monitoring is a most useful aid in rationalising drug therapy and improving seizure control.