Major
Haloperidol × tacrolimus
First-generation antipsychotics. Butyrophenone derivatives×Calcineurin inhibitor (immunosuppressant)
Mechanism
Additive QT prolongation. Haloperidol strongly prolongs QT, especially parenterally (IV). Tacrolimus prolongs QT with hypomagnesaemia. Combined action raises torsades de pointes risk.
Symptoms
QT prolongation on ECG, dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.
Management
Avoid the combination, especially IV haloperidol. Alternative antipsychotics with minimal QT effect post-transplant: olanzapine or aripiprazole. For acute delirium: dexmedetomidine (no QT effect).