Amiodarone
NICE BNF Amiodarone
Monitoring
Thyroid Function Tests (TFTs)
Rationale: amiodarone can induce thyroid dysfunction – both hypothyroidism and thyrotoxicosis (common to very common)
- Amiodarone-induced thyrotoxicosis can be sub-classified depending on the pathophysiology
- Type 1: iodine-induced hyperthyroidism (amiodarone is iodine-rich) (goitre and increased Dopper flow are common)
- Type 2: destructive thyroiditis (lack of goitre and Doppler flow)
- Amiodarone-induced hypothyroidism results from amiodarone’s iodine content due to the Wolff-Chaikoff effect (excess iodine temporarily inhibits thyroid hormone synthesis)
Timing
- Before treatment
- During treatment: 6-monthly
- After treatment: for several months (especially in the elderly)
Management of amiodarone-induced thyroid dysfunction:
| Condition | Pathophysiology | Amiodarone discontinuation | 1st line management | Further management |
|---|---|---|---|---|
| Amiodarone-induced thyrotoxicosis type 1 | Iodine-induced hyperthyroidism | Consider if feasible (e.g. an alternative antiarrhythmic is possible)
Amiodarone is continued in many cases, due to the lack of an alternative antiarrhythmic. Decision should be made with cardiology, weighing the risk of arrhythmia recurrence against further thyrotoxicosis |
High-dose thionamides (e.g. carbimazole, methimazole) | Potassium perchlorate (blocks iodine uptake) |
| Amiodarone-induced thyrotoxicosis type 2 | Destructive thyroiditis | Oral steroids | IV steroids
Last resort: thyroidectomy |
|
| Amiodarone-induced hypothyroidism | Wolff-Chaikoff effect | Usually continued | Levothyroxine replacement |
Liver Function Test (LFT)
Rationale
- Hepatotoxic medication
- If severe LFT abnormalities OR clinical signs of liver disease develop ⇒ Stop amiodarone
Timing
- Before treatment
- During treatment: 6-monthly
Chest X-Ray
Rationale:
- Pulmonary toxicity: especially pulmonary fibrosis (common to very common)
- Pulmonary toxicity is usually reversible if amiodarone is stopped promptly
Timing:
- Before treatment (baseline)
NB – If pulmonary toxicity suspected during treatment a repeat CXR or CT scan should be conducted
Electrolytes (Potassium)
Rationale
- Normal potassium levels maximise the therapeutic benefit of amiodarone, and decrease its pro-arrhythmic risk
Timing
- Before treatment: Serum potassium
Additional (IV use)
- Ensure ECG monitoring and available resuscitation facilities
- Close LFT monitoring
Summary Table
| Test | Timing |
|---|---|
| TFTs |
|
| LFTs |
|
| CXR |
|
| Electrolytes (K+) |
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