Major
Carbamazepine × isotretinoin
Antiepileptics. Carboxamide derivatives×Systemic retinoid (vitamin A derivative)
Mechanism
Carbamazepine is a CYP3A4 inducer. It lowers isotretinoin plasma levels, which can cause acne therapy failure. Additionally: both drugs are teratogens, absolutely contraindicated in pregnancy.
Symptoms
Recurrence of acne, no response to isotretinoin. In pregnancy on combination: severe foetal malformations (both drugs are teratogens).
Management
Avoid the combination. Alternative anticonvulsants without induction: levetiracetam, lamotrigine. Alternative acne therapy: antibiotics (doxycycline, azithromycin), topical retinoids, spironolactone in women. In women of reproductive age, mandatory dual contraception.