Amiodarone toxicity and monitoring

The MHRA describes amiodarone as generally reserved for situations when other treatments cannot be used or have failed, with treatment started and monitored under hospital or specialist supervision. It acts on the heart rhythm in several ways, but it also accumulates in tissues. Its plasma half-life of around 50 days means that any adverse effect may persist for a month or more after treatment stops.

The MHRA reminded healthcare professionals in 2022 that amiodarone has been associated with serious and potentially life-threatening effects, particularly of the lung, liver and thyroid gland, that patients should be supervised and reviewed regularly, and that the product has many drug interactions. The information was updated again in May 2026 to refresh links to the patient card and the product characteristics.

Amiodarone can commonly cause lung inflammation (pneumonitis), which in some cases progresses to thickening or scarring of the lung (fibrosis) and can be life-threatening. Symptoms can include breathlessness that seems out of proportion to the heart condition, a dry cough, fatigue, weight loss and fever. The MHRA says pulmonary toxicity is usually, but not always, reversible after early withdrawal, with or without corticosteroid treatment.

After a coroner raised concerns about the lack of a requirement for lung imaging in long-term users, the MHRA sought expert advice. The experts concluded that regular lung imaging may expose patients to unnecessary radiation, can be alarming, and is not needed because patient-reported worsening breathing is usually a good first indicator. A baseline clinical evaluation, with consideration of a chest X-ray, is advised before starting, and CT scans are more specific than X-rays if toxicity is suspected. Patients are told the lung problem may start at any time during treatment or in the month after stopping.

Amiodarone can commonly lead to an underactive or overactive thyroid, especially in people with a history of thyroid disorders, in whom the MHRA says treatment is contraindicated. Thyroid tests should be checked before treatment, at 6-monthly intervals and for several months after stopping. Possible signs include weakness, weight change, heat or cold intolerance, hair thinning, sweating, menstrual changes, a swollen neck, nervousness and trouble concentrating.

Liver function should likewise be checked before starting and at 6-monthly intervals. The warning signs given to patients are yellowing of the skin or eyes, tiredness or sickness, loss of appetite, stomach pain or a high temperature.

The MHRA lists serious reactions affecting the eyes, heart, lungs, liver, thyroid, skin and peripheral nervous system, and says patients should have tests of blood, lungs, heartbeat and eyes before and during treatment as advised. Patients are told to stop amiodarone and see a doctor or go to hospital straight away if they have any loss of eyesight, or if the heartbeat becomes more uneven or very slow.

The skin and peripheral nerves are among the organs the MHRA lists, so new rashes, tingling or weakness in the limbs should be mentioned promptly rather than put down to age or the heart condition.

Amiodarone interacts with many medicines, so the summary of product characteristics advice must be followed closely. Always show the patient card when you see a new doctor, dentist or pharmacist, and check before starting any new prescription, over-the-counter or herbal medicine. The MHRA has also published separate safety information about severe slow heart rate and heart block when amiodarone is taken with certain hepatitis C medicines.

If any of the warning symptoms appear, the MHRA advice to patients is to stop taking amiodarone and see a doctor or go to hospital straight away, during treatment or in the period after stopping. Do not stop it for other reasons without medical advice, because it is treating a significant heart rhythm problem.

Patients, carers and clinicians can report suspected reactions through the Yellow Card scheme. Between hospital and GP, agree who arranges the 6-monthly blood tests and keep a record of the results. Remember that thyroid checks continue for several months after the drug is stopped, and that reactions can still arise after the last dose because of the drug's long half-life.