Major
citalopram × venlafaxine
SSRI (selective serotonin reuptake inhibitor)×SNRI (serotonin-norepinephrine reuptake inhibitor)
Mechanism
SSRI + SNRI – serotonin syndrome, additive QT prolongation at high venlafaxine doses.
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 not prescribed. When switching antidepressants, allow a 1-week washout. For augmentation, use mirtazapine or agomelatine.