Free level monitoring of carbamazepine and valproic acid: clinical significance.

The recently available ultrafiltration technique facilitates determination of the free drug serum concentration of several antiepileptic drugs. For this reason a reappraisal of the clinical significance of free level monitoring was thought necessary. In this study on 203 patients receiving carbamazepine monotherapy and 101 patients receiving valproic acid monotherapy, the total and free drug levels were correlated with therapeutic outcome and side effects. Our investigations indicated no closer correlation between free concentration and seizure reduction or side effects than between total concentration and effectiveness or side effects. However, we found a close correlation between total and free concentrations.