Introduction

Amiodarone is a medicine used in the treatment of tachyarrhythmias. Here, we review the top facts about amiodarone that you need to know; what it’s used for, how it works, and what side effects and drug interactions it’s linked to.

Amiodarone was first discovered in 1961 and, one year later, it entered mainstream medical use in the treatment of angina. However, its side effect profile proved to be a challenge and so the drug was briefly withdrawn in 1967.

Seven years later, though, and amiodarone was found to be effective in the treatment of arrhythmias – and what it continues to be used today for. It remains on the WHO List of Essential Medicines.

It trades under a variety of brands including Cordarone and Nexterone.

Amiodarone is available by mouth and intravenous use.

Let’s now take a deeper look at what amiodarone is, how it works and what side effects and drug interactions it’s linked to. You can expect at least one NAPLEX question on amiodarone over the course of your pharmacy license exam.

Facts about Amiodarone

Here are our top ten facts about amiodarone that you need to know!

• Amiodarone is used in the management of a wide range of tachyarrhythmias including atrial fibrillation, atrial flutter, supraventricular tachycardia, ventricular tachycardia and refractory ventricular fibrillation. Amiodarone is most likely used when other treatment options have proven insufficient.
• Amiodarone works by reducing automaticity (spontaneous depolarisation), slowing conduction velocity and increasing refractoriness (resistance to depolarisation) – including the AV node. Due to its effects at the AV node, amiodarone reduces the ventricular rate in patients with AF and atrial flutter. Amiodarone also works by breaking re-entry circuits and restoring sinus rhythm (in, for example, SVT with a re-entry circuit that includes the AV node).
• Amiodarone is classified as a Class III antiarrhythmic drug. As well as blocking potassium channels, the drug also blocks sodium and calcium channels too. Amiodarone also antagonises both alpha- and beta-adrenergic receptors.
• The major active metabolite of amiodarone is desethylamiodarone.
• Amiodarone is renowned for its pronounced adverse effect profile. Side effects include hypotension, interstitial lung disease, thyroid abnormalities (both overactive and underactive), corneal microdeposits, abnormal liver enzymes, light-sensitive blue-gray skin discoloration and, particularly with long-term use, peripheral neuropathies. Amiodarone can also cause serious cardiac effects such as bradycardia and AV block. Many serious effects are typically a consequence of long-term, chronic use.
• Amiodarone should be avoided in patients with heart block, severe hypotension and in cases of active thyroid disease.
• Amiodarone increases plasma concentrations of drugs such as diltiazem, digoxin and verapamil – increasing the risk of bradycardia, heart failure and AV block. Preferably doses are reduced (often by half) if they must be taken alongside amiodarone.Amiodarone inhibits the clearance of warfarin.
• Concurrent use of amiodarone with grapefruit juice elevates serum amiodarone levels. Amiodarone is extensively metabolised by CYP 3A4.
• Amiodarone should be avoided in pregnancy. Furthermore, amiodarone can be expressed in breast milk and so mothers may be advised to stop nursing.
• Amiodarone is often a last-line treatment option, once other safer means have been exhausted. Given the serious nature of the drug, it always required senior medical involvement. It should not be administered by a foundation doctor. However, cardiac arrest is often an exception to this rule. For VF or pulseless VT immediately after the third shock of an ALS algorithm, the standard dose is 300mg IV, followed by 0.9% sodium chloride (or 5% glucose as a flush).

Amiodarone is an effective, but serious medicine. Above, we’ve put together the top ten facts about amiodarone you at least need to know.Of course, don’t stop there. Use these facts as the basis upon which to learn more about this important drug.

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