Carbamazepine × Isotretinoin

Isotretinoin alters the absorption and clearance of carbamazepine and its active metabolite, carbamazepine-10,11-epoxide; the carbamazepine SmPC lists isotretinoin among drugs that can lower carbamazepine levels. The labels do not describe any effect of carbamazepine on isotretinoin. The second risk concerns pregnancy: carbamazepine speeds up the breakdown of hormonal contraceptives and can make them fail (carbamazepine SmPC), while isotretinoin causes severe birth defects at a high rate and is contraindicated in pregnancy (isotretinoin SmPC).

If carbamazepine levels fall, seizures may return. Excess carbamazepine epoxide causes dizziness, somnolence, ataxia and double vision. If hormonal contraception fails and pregnancy occurs, isotretinoin exposes the fetus to severe birth defects.

The pair is not banned. When isotretinoin is started or stopped, carbamazepine blood levels are checked, as the carbamazepine SmPC requires, and the carbamazepine dose is adjusted if needed (carbamazepine SmPC). Women who can become pregnant receive isotretinoin only within the pregnancy prevention programme: effective contraception without breaks from 1 month before starting, throughout treatment and for 1 month after, with at least one highly effective user-independent method or two complementary methods; pregnancy tests before, during (ideally monthly) and 1 month after treatment (isotretinoin SmPC). Hormonal contraceptives may fail with carbamazepine, so other effective methods are chosen, for example an intrauterine device (carbamazepine SmPC).