MajorClass III antiarrhythmics (Vaughan Williams)×Thiazide diuretics
Updated · Methodology
Mechanism
Hydrochlorothiazide (thiazide 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.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Summary of a multi-drug list →
Medicine list: everything you take in one place →
Sources
- Lexicomp: Lexicomp Drug Interactions (2024)– Wolters Kluwer Clinical Drug Information, Inc. Lexi-Interact Online, 2024
- Pharmaceutical Press: Stockley's Drug Interactions, 12th edition (2024)– Preston CL (ed.). Stockley's Drug Interactions. 12th ed. London: Pharmaceutical Press; 2024
- AEMPS: Ficha técnica: Hidroclorotiazida (nº registro 86487), sección 4.5 (2026)– AEMPS, CIMA, nº registro 86487, revisión 09/2026, sección 4.5