Precursor to metabolite: Carbamazepine ER (Equetro) to Carbamazepine-10,11-epoxide

Carbamazepine ER (Equetro) is converted to Carbamazepine-10,11-epoxide by CYP3A4.

The pair

Carbamazepine ER (Equetro) — Carbamazepine ER capsule - the only carbamazepine approved for acute bipolar mania.
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 ER (Equetro) and Carbamazepine-10,11-epoxide.