Major
Doxycycline × isotretinoin
Tetracyclines×Systemic retinoid (vitamin A derivative)
Mechanism
Both drugs cause benign intracranial hypertension (pseudotumor cerebri). Additive risk with classic presentation: headache, diplopia, visual disturbance, optic disc oedema.
Symptoms
Persistent pressing headache (not relieved by analgesics), diplopia, transient visual disturbances, tinnitus. Examination: optic disc oedema, blind spot enlargement. Symptoms appear several weeks into combination.
Management
The combination is not prescribed. Alternative antibiotic for acne on isotretinoin: azithromycin (short course) or topical retinoids. If headache with diplopia appears, stop both drugs immediately and refer to ophthalmology.