Major
Amitriptyline × citalopram
Tricyclic antidepressants (TCA)×SSRI (selective serotonin reuptake inhibitor)
Mechanism
Both drugs prolong QT and are serotonergic. Citalopram weakly blocks CYP2D6, a partial amitriptyline route, so amitriptyline levels rise modestly.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
Avoid the combination. Alternative antidepressants if citalopram fails: mirtazapine or agomelatine. For neuropathic pain, replace amitriptyline with gabapentin or pregabalin.