Amitriptyline × Escitalopram

The escitalopram SmPC (AEMPS, sections 4.3 and 4.5) lists tricyclic antidepressants among QT-prolonging drugs and contraindicates their concomitant use. The combination has not been studied, and an additive effect on repolarisation cannot be excluded. Two more mechanisms sit on top of QT. Serotonergic: the amitriptyline SmPC calls for caution with SSRIs because of serotonin syndrome. Kinetic: amitriptyline is metabolised mainly through CYP2D6 and CYP2C19, escitalopram inhibits CYP2D6, and tricyclic levels rise. The amitriptyline label does not name escitalopram among potent CYP2D6 inhibitors, but the Lexapro label reports a direct tricyclic experiment: escitalopram 20 mg/day raised desipramine Cmax by 40% and AUC by 100%.

Serotonin syndrome: agitation, confusion, tremor, myoclonus, hyperthermia, tachycardia. QT prolongation on ECG up to torsade de pointes. The amitriptyline label singles out marked bradycardia, decompensated heart failure and electrolyte disturbance (hypokalaemia, hyperkalaemia, hypomagnesaemia) as the vulnerable situations. As amitriptyline levels rise, its dose-dependent effects grow stronger: dry mouth, constipation, urinary retention, orthostatic hypotension, confusion in older patients.

The escitalopram label files this combination under contraindications, so ECG monitoring and dose reduction do not settle it, and one of the two drugs goes. Where a tricyclic is already running alongside a CYP2D6 inhibitor, the amitriptyline label describes monitoring tricyclic plasma levels and adjusting the dose. The two regulators diverge. The FDA Lexapro label stops at caution and monitoring, the AEMPS SmPC files the combination under contraindications, and the severity here follows the stricter European document. For neuropathic pain NICE CG173 puts four drugs in the first line – amitriptyline, duloxetine, gabapentin and pregabalin – so dropping amitriptyline leaves three. Duloxetine among them is serotonergic too.