Amiodarone

How it works

It predominantly blocks potassium channels to prolong the cardiac action potential and refractory period, with additional sodium and calcium channel blockade and non-competitive beta-adrenergic antagonism.

Prescribing in practice

• Amiodarone causes serious cumulative organ toxicity (thyroid, hepatic, pulmonary and ocular) and prolongs the QT interval, so it requires baseline assessment, ongoing surveillance and careful review of QT-prolonging and interacting drugs.
• Its very long half-life means effects and interactions, including potentiation of warfarin and raised digoxin levels, persist for weeks after stopping.
• Intravenous use can cause severe hypotension and, with peripheral lines, phlebitis, so central access is preferred for prolonged infusion.

Monitoring

Monitor thyroid and liver function at baseline and periodically, with chest imaging and ophthalmic review as indicated, alongside ECG surveillance.

Counselling the patient

• Use sun protection as the skin becomes very sensitive to sunlight.
• Report breathlessness, persistent cough, visual changes or symptoms of thyroid disturbance.
• Avoid grapefruit juice and tell any prescriber you take amiodarone, as interactions persist after stopping.

Evidence & guidelines

Amiodarone features in resuscitation guidance for shock-refractory ventricular fibrillation and pulseless ventricular tachycardia and in NICE atrial fibrillation guidance, with MHRA advice reinforcing its monitoring requirements.