CARBAMAZEPINE AND LAMOTRIGINE

Most studies have found that lamotrigine has no effect on the pharmacokinetics of carbamazepine or its active epoxide metabolite. However, some studies have found that lamotrigine raises the serum levels of carbamazepine-epoxide. Carbamazepine reduces lamotrigine levels. Toxicity has been seen irrespective of changes in levels.
Overall lamotrigine does not appear to significantly alter carbamazepine levels. However, toxicity has occurred, therefore patients should be well monitored if lamotrigine is added, and the carbamazepine dose reduced if CNS adverse effects occur. Carbamazepine induces the metabolism of lamotrigine, and the recom- mended starting dose and long-term maintenance dose of lamotrigine in patients already taking carbamazepine is twice that of patients receiving lamotrigine monotherapy. However, if they are also taking valproate in addition to carbamazepine, the lamotrigine dose should be reduced.