Amiodarone × Hydrochlorothiazide

Hydrochlorothiazide (thiazide diuretic) increases potassium and magnesium loss. Low levels amplify amiodarone's QT-prolonging effect.

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.

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.