Valproate can inhibit carbamazepine metabolic pathways, resulting in raised carbamazepine-epoxide concentrations. [1] Valproate can also displace protein-bound carbamazepine and therefore increase the levels of free carbamazepine. This may result in neurotoxicity even when valproate levels are low.[2]
Carbamazepine induces metabolism of both itself and valproate via Cytochrome P450 3A3/4 system, which may decrease the serum concentrations of both drugs and increase the risk of relapse.[2]