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Atrial fibrillation - Management
What key drug interactions should I be aware of for amiodarone?
- Beta-blockers
- Only specialists should co-prescribe beta-blockers and amiodarone. Hypotension, bradycardia, ventricular fibrillation, and asystole have been seen in a few people given amiodarone with propranolol, metoprolol, or sotalol.
- Calcium-channel blockers
- Amiodarone should be avoided or used with caution with diltiazem or verapamil because cardiac depression can occur.
- Drugs that prolong the QT interval
- Only specialists should co-prescribe drugs that prolong the QT interval. This is because of the risk of additive effects, which may lead to serious and potentially life-threatening torsades de pointes arrhythmias. Examples of drugs that are known to have a high risk of causing QT prolongation include:
- Antiarrhythmics, such as sotalol, disopyramide, and quinidine.
- Antihistamines, such as astemizole.
- Antipsychotics, such as amisulpride, haloperidol, and droperidol.
- Simvastatin
- Rarely, myopathy and rhabdomyolysis have been reported in people taking amiodarone with high doses of simvastatin. The dose of simvastatin should not exceed 20 mg each day in people taking amiodarone unless the clinical benefit is likely to outweigh the increased risk of myopathy and rhabdomyolysis.
- Warfarin
- The anticoagulant effects of warfarin are increased by amiodarone. The onset of this interaction may be slow (up to 2 weeks), with the peak effect occurring about 7 weeks after warfarin treatment is started. The dose of warfarin should be reduced by one-third to two-thirds if amiodarone is added. The international normalized ratio should be monitored once a week for the first 7 weeks of concurrent treatment.
- Digoxin
- Amiodarone increases levels of digoxin because of reduced renal digoxin clearance. The dose of digoxin should be reduced by half, and concentrations of digoxin should be monitored closely in view of potential toxicity.
- Grapefruit
- People taking amiodarone should not eat grapefruit or drink grapefruit juice. Grapefruit appears to completely inhibit the metabolism of amiodarone to its major active metabolite.
Amiodarone has a long half-life (25–100 days); thus, interactions may occur for some time after drug withdrawal.
Basis for recommendation
- These recommendations are based on Stockley's drug interactions: a source book of interactions, their mechanisms, clinical importance and management [Baxter, 2008] and published expert opinion [DTB, 2003].
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