Major
citalopram × Mirtazapine
SSRI (selective serotonin reuptake inhibitor)×Other antidepressants (NaSSA)
Mechanism
Mirtazapine increases serotonergic transmission via α2-adrenergic blockade and blocks 5-HT2A/2C. Serotonin syndrome is rare with citalopram but possible at high doses. Citalopram itself prolongs QT.
Symptoms
Serotonin syndrome: agitation, confusion, tremor, myoclonus, hyperreflexia. Autonomic features: sweating, tachycardia, hypertension, fever. First signs appear within hours of co-administration.
Management
The combination is used for antidepressant augmentation. Cap citalopram at 20 mg and mirtazapine at 30 mg/day. Monitor blood pressure, pulse, and mental status in the early weeks.