Use of total and free anticonvulsant serum levels in clinical practice

Total and free (unbound) anticonvulsant drug levels in serum (361 analyses) were measured in a series of 117 patients who attended for routine management of epilepsy. Comparison of predetermined therapeutic ranges for the two types of level demonstrated disagreement in as many as 30% of assessments. The clinical significance of this finding is discussed and wider acceptance of the use of free drug levels in the management of epilepsy is advocated.