Amitriptyline × Citalopram

Amitriptyline is a tricyclic antidepressant, and tricyclics are named among QT-prolonging drugs in both SSRI labels. Its own SmPC calls for caution with SSRIs because of serotonin syndrome. The citalopram SmPC lists ongoing treatment with any drug capable of prolonging the QT interval among its contraindications, with no exceptions. The kinetic part is weaker here than with escitalopram: the SmPC calls citalopram a weak CYP2D6 inhibitor and notes that with substrates of that enzyme, amitriptyline included, no clinically meaningful changes were seen. QT and serotonin remain the drivers.

QTc prolongation on ECG, palpitations, dizziness, syncope, with torsade at the far end. Serotonin syndrome is tracked separately: agitation, confusion, tremor, myoclonus, sweating, hyperthermia. Arrhythmia risk is higher with hypokalaemia, hypomagnesaemia and bradycardia.

The pair sits in the citalopram SmPC contraindications, so the question is which drug stays, not how far to cut the dose. Beyond QT there is kinetics: amitriptyline runs through CYP2D6 and CYP2C19, and inhibiting either path raises its levels. For such combinations the amitriptyline label describes plasma level monitoring and dose adjustment.