Precursor to metabolite: Carbamazepine XR to Carbamazepine-10,11-epoxide

Carbamazepine XR is converted to Carbamazepine-10,11-epoxide by CYP3A4.

The pair

Carbamazepine XR — Extended-release carbamazepine for seizures and trigeminal neuralgia; potent enzyme inducer.
Carbamazepine-10,11-epoxide — Active epoxide metabolite of carbamazepine; cleared by epoxide hydrolase, which valproate inhibits.

Anything that inhibits or induces CYP3A4 shifts the balance between Carbamazepine XR and Carbamazepine-10,11-epoxide.