Therapeutic Drug Monitoring of Lamotrigine in Patients Suffering from Resistant Partial Seizures

Sixty patients, all potential candidates for ongoing lamotrigine (LTG) treatment as add-on therapy for resistant partial seizures and receiving carbamazepine (CBZ) and/or valproate (VPA) treatment, were submitted to therapeutic drug monitoring (TDM). The aim was to evaluate the possible relation between serum levels and the clinical effect of LTG, to verify whether CNS toxicity has to be considered the result of a pharmacokinetic or a pharmacodynamic interaction with CBZ, and to investigate whether possible changes in the clinical response during long-term treatment are dependent on LTG serum level variations. Sixteen patients achieved complete control, 26 a ≧50% reduction in seizures, the remainder did not respond. Mean LTG serum concentrations were higher in responders than in nonresponders, the difference being statistically insignificant. The best results were observed in VPA-cotreated patients with the highest LTG blood levels. CNS toxicity occurred after giving LTG to subjects who subsequently developed the highest LTG concentrations, whereas CNS toxicity seemed unrelated to CBZ and CBZ-epoxide serum concentrations. No decrease in LTG, CBZ and VPA serum levels was observed even in patients showing a reduction in the response during long-term treatment.