Major
Amiodarone × Indapamide
Class III antiarrhythmics (Vaughan Williams)×Thiazide-like diuretics
Mechanism
Indapamide (thiazide-like diuretic) increases potassium and magnesium loss. Low levels amplify amiodarone's QT-prolonging effect.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
The combination is common (hypertension plus atrial fibrillation). Check potassium and magnesium every 3 months; if potassium drops below 4.0 mmol/L, add a potassium-sparing diuretic or potassium supplement.