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.