Amiodarone is an effective anti-arrhythmic medication which belongs to class III of the Vaughan-Williams classification.
The half life of amiodarone is long at 20 to 107 days – this means there is the potential for drug interactions to occur even months after treatment has stopped.
Multiple drug interactions may occur, including:
- Warfarin – inhibits metabolism → enhanced anti-coagulant effect
- TCA – avoid concurrent use as increased risk of ventricular arrhythmias
- Phenytoin – inhibits metabolism → increased plasma concentration
- Digoxin – increases plasma concentration; half digoxin dose
- Beta blockers – risk of AV block and ventricular arrhythmias
- Calcium channel blockers – risk of AV block
- Grapefruit juice – increases the plasma concentration of amiodarone
- Cimetidine – increases plasma concentration of amiodarone
Amiodarone is also renowned for its side effects which include:
- Slate-grey discoloration of the face
- Occurs in 1-7%
- Corneal microdeposits
- reversible on stopping treatment
- associated with night glare
- found in nearly 100% of patients
- Taste disturbance
- Photosensitivity
- Thyroid dysfunction (hyper and hypothyroidism)
- Occurs as amiodarone contains iodine
- If thyrotoxicosis occurs – should usually withdraw amiodarone at least temporarily
- If hypothyroidism occurs amiodarone can be continued if it is essential
- Between 2 and 12% of patients may develop thyrotoxicosis and between 6 to 13% develop hypothyroidism
- Pulmonary toxicity
- occurs in 5-10%
- may be pulmonary fibrosis or interstitial pneumonitis
- Arrhythmias
- Hepatotoxicity
- raised serum transaminases occur in 15-20%
- Neurological side effects
- Peripheral neuropathy
- Tremor
- Ataxia – very rarely
- Alopecia – very rarely
- Hypokalaemia
LFTs and TFTs should be done before commencing treatment and then every 6 months. A CXR should also be performed prior to commencing treatment.
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