Carbamazepine is extensively metabolised by CYP3A4 to the active 10,11-epoxide
metabolite, which is then further metabolised. Concurrent use of CYP3A4 inhibitors or inducers may therefore lead to
toxicity or reduced
efficacy. However, importantly,
carbamazepine also induces CYP3A4 and so induces its own
metabolism (auto- induction). Because of this, it is important that drug interaction studies are multiple- dose and carried out at steady state. Auto-induction also means that moderate inducers of CYP3A4 may have less effect on steady-state
carbamazepine levels than expected.
Carbamazepine can also act as an inhibitor of CYP2C19.