Amiodarone: heart rhythm medicine, monitoring and long-lasting effects

Amiodarone is a prescription-only medicine that stabilises the heart's electrical activity. The SmPC describes it for severe rhythm disorders when other treatments cannot be used, naming atrial fibrillation, ventricular tachycardias and Wolff-Parkinson-White syndrome.

Because it can affect several organs, the SmPC stresses using the minimum effective dose to keep side effects down.

The SmPC sets out a loading phase: 200mg three times daily for one week, then 200mg twice daily for a week, then a maintenance dose of 200mg daily or less. Your specialist adapts this to you, so follow the label you have been given.

Its very long half-life, around 50 days according to the SmPC, means that a missed dose does not cause an immediate loss of effect. Even so, take it as prescribed and speak to your doctor or pharmacist if you miss doses.

The SmPC lists these contraindications: a slow heart rate (sinus bradycardia) or heart block without a pacemaker, a history of thyroid dysfunction, hypersensitivity to iodine, pregnancy and breastfeeding, and use alongside medicines that prolong the QT interval.

Because thyroid dysfunction is on the contraindication list and the SmPC asks for baseline testing, a thyroid assessment before treatment is part of getting started.

Thyroid: amiodarone can cause an underactive or overactive thyroid, so baseline testing and ongoing monitoring, described in the SmPC as about every six months, are needed. Lungs: inflammation or scarring of lung tissue is a risk, so new breathlessness or cough should be reported, and chest imaging is part of assessment. Liver: liver function is monitored and the dose reduced if enzyme levels rise above three times normal.

Eyes and skin: corneal deposits, usually harmless, can occur, and the skin may burn easily in sunlight, so sun protection matters. Rare severe skin reactions such as Stevens-Johnson syndrome are also described. Cardiac effects include a very slow heart rate and conduction problems, especially in older people.

• Report new breathlessness, dry cough or chest discomfort promptly.

• Use high-factor sun protection and cover up in strong sunlight.

• Keep blood test appointments for thyroid and liver checks.

The SmPC highlights these: beta blockers and the calcium channel blockers diltiazem and verapamil increase the risk of a slow heart rate; amiodarone significantly raises digoxin levels, so the digoxin dose is halved; it inhibits the metabolism of warfarin and so INR monitoring needs to be more frequent; hepatitis C treatments containing sofosbuvir carry a risk of serious bradycardia; and grapefruit juice should be avoided.

Because amiodarone lingers for months, interactions can persist long after the last tablet. Always tell new prescribers you have taken it recently.

Amiodarone is contraindicated in pregnancy and breastfeeding according to the SmPC, so talk to your doctor before conception if you are on it. Do not stop suddenly without cardiology advice, since the rhythm problem may return.

Suspected side effects can be reported through the MHRA Yellow Card scheme. The patient leaflet for the 200mg tablets is available from the emc.