From the Guidelines
Monitoring for amiodarone therapy should include baseline and periodic assessments of thyroid, liver, and pulmonary function, as well as regular electrocardiograms (ECGs), as recommended by the most recent guidelines 1. When initiating amiodarone therapy, it is essential to obtain baseline measurements, including:
- Thyroid function tests (TSH, free T4)
- Liver enzymes (AST, ALT)
- Chest X-ray
- Pulmonary function tests
- ECG
- Ophthalmologic examination
During therapy, the following monitoring schedule is recommended:
- Thyroid function every 3-6 months
- Liver enzymes every 6 months
- Annual chest X-rays and pulmonary function tests
- Regular ECGs to assess QT interval and detect potential arrhythmias
- Routine ophthalmologic exams to check for corneal deposits and optic neuropathy
This comprehensive monitoring is necessary due to amiodarone's long half-life and potential to cause toxicity in multiple organ systems, including hypothyroidism or hyperthyroidism, hepatotoxicity, pulmonary fibrosis, and cardiac conduction abnormalities, as highlighted in the guidelines 1 and supported by earlier studies 1. Patients should be educated to report symptoms such as shortness of breath, cough, visual changes, tremors, weight changes, or yellowing of the skin, which may indicate developing toxicity.
From the FDA Drug Label
Because of the slow elimination of amiodarone and its metabolites, high plasma iodide levels, altered thyroid function, and abnormal thyroid-function tests may persist for several weeks or even months following amiodarone withdrawal. Hypothyroidism has been reported in 2 to 4% of patients in most series, but in 8 to 10% in some series Hyperthyroidism occurs in about 2% of patients receiving amiodarone, but the incidence may be higher among patients with prior inadequate dietary iodine intake IF ANY NEW SIGNS OF ARRHYTHMIA APPEAR, THE POSSIBILITY OF HYPERTHYROIDISM SHOULD BE CONSIDERED.
The recommended monitoring for amiodarone therapy includes:
- Thyroid function tests: to monitor for hypothyroidism and hyperthyroidism, as amiodarone can cause altered thyroid function and abnormal thyroid-function tests.
- Serum TSH levels: to identify hypothyroidism, as elevated serum TSH levels can indicate this condition.
- Serum T3 and T4 levels: to monitor for hyperthyroidism, as abnormally elevated levels of these hormones can indicate this condition.
- Clinical symptoms and signs: to monitor for signs of hypothyroidism and hyperthyroidism, such as arrhythmias, and to consider the possibility of hyperthyroidism if new signs of arrhythmia appear. 2
From the Research
Recommended Monitoring for Amiodarone Therapy
- Laboratory monitoring rates for liver, thyroid, and pulmonary function should be performed regularly in patients treated with amiodarone, as recommended by guidelines 3, 4.
- Baseline measurements of renal, liver, thyroid, and pulmonary function, as well as electrocardiogram and chest X-ray, should be taken before initiating amiodarone therapy 4.
- Thyroid function tests, including TSH, free T4, and free T3, should be performed regularly during amiodarone treatment, as thyroid dysfunction is a common adverse effect 5, 6.
- Monitoring of liver function, including ALT, should be performed regularly during amiodarone treatment, as liver toxicity is a potential adverse effect 3.
- Pulmonary function tests, including diffusion capacity of carbon monoxide tests (DLCO) and annual chest X-rays (CXR), should be performed regularly during amiodarone treatment, as pulmonary toxicity is a potential adverse effect 3.
- Regular follow-up of thyroid function under amiodarone usage is crucial, but the rate of adherence to guidelines is often suboptimal 7.
Factors Associated with Adequate Monitoring
- Physicians' expertise, particularly cardiologists and electrophysiologists, is significantly associated with adequate thyroid monitoring 7.
- Years of service are also associated with adequate monitoring, with less experienced physicians being more likely to adhere to guidelines 7.
- Patient characteristics, such as younger age and female sex, are associated with a higher likelihood of baseline thyroid function testing 7.