Unusual Features
Amiodarone has several characteristics that make it unique among the antiarrhythmic drugs, and even among drugs in general.
Long Loading Time
When taken by mouth, amiodarone takes weeks to achieve its maximum effectiveness, and for a very unusual reason. While most drugs circulate in the bloodstream for a while until they are metabolized or excreted, amiodarone is stored in the body’s tissues.
The full antiarrhythmic effects of the drug are not achieved until the tissues are sufficiently saturated with amiodarone. So, the drug has to be “loaded” before it becomes optimally effective.
Amiodarone also can be administered intravenously (with much more rapid effect) when treating arrhythmia is urgent. However, switching from intravenous to oral dosing has to be done carefully, since the drug still has to be loaded for a prolonged period of time for chronic usage.
Long Half-Life
Amiodarone leaves the body very, very slowly. It is not excreted to an appreciable extent by the liver or the kidneys. (Amiodarone is metabolized in the liver to desethylamiodarone, which has the same antiarrhythmic and toxic effects as amiodarone, and which also remains in the body for a very long time.)
For the most part, amiodarone and its metabolites are removed from the body when amiodarone-containing cells are lost. These include, for example, skin cells or cells from the gastrointestinal tract, which are shed by the millions each day. This is a long, slow process.
Thus, even if it is determined that it is necessary to stop amiodarone (because of side effects, for instance), the drug remains in the body in measurable quantities for a very long time after the last dose is taken.
Different Mechanisms
Amiodarone works through many different mechanisms, unlike most drugs. It is a both a Class I and a Class III antiarrhythmic drug, and it also acts as a beta-blocker and as a calcium blocker (Class II and IV).
It dilates blood vessels and often acts to modify the effect of thyroid hormone.
All of these effects contribute to its ability to treat arrhythmias and probably account for amiodarone’s unique effectiveness.
Side Effects
Because amiodarone is stored in many different tissues within the body, it can produce side effects affecting many different organs. Some of these side effects can take months or years to develop, so anyone taking this drug must always be on the lookout.
Furthermore, the side effects of amiodarone tend to be very unusual for antiarrhythmic drugs—or any drug, for that matter.
For these reasons, when amiodarone first came into clinical usage, it took more than a decade for healthcare providers to recognize that many of the strange symptoms they were seeing were being caused by amiodarone.
Here are some of the more distinctive side effects that can be seen with amiodarone:
Deposits on the corneas: Amiodarone commonly causes deposits to form on the cornea of the eyes, occasionally leading to “halo vision,” where looking at bright lights at night is like looking at the moon on a foggy evening. Skin discoloration: Amiodarone can cause a disfiguring (and possibly permanent) blue-grey discoloration of the skin, generally in areas of sun exposure. Sun sensitivity: Amiodarone often sensitizes the skin to sunlight to the point that even trivial exposure can cause a sunburn. Thyroid problems: Amiodarone can cause thyroid disorders, both hypothyroidism (low thyroid) and hyperthyroidism (high thyroid). These thyroid problems are quite common with amiodarone and can be serious. For this reason, patients taking this drug should have their thyroid function routinely monitored. Liver toxicity: Since amiodarone can cause liver toxicity, liver enzymes need to be monitored periodically. Stomach upset: Amiodarone often causes some nausea, vomiting, or loss of appetite. Lung toxicity: The most dreaded side effect of amiodarone, lung toxicity can take several forms. It may cause an acute lung syndrome that makes patients desperately ill, requires intensive care, and often results in death. Or, it can cause a more insidious, gradual, unnoticeable, stiffening of the lungs that both the healthcare provider and patient can overlook until severe, probably irreversible lung damage is done.
When Should Amiodarone Be Used?
Because of the unique difficulties and risks of using amiodarone, this drug should be used only in people whose arrhythmias are life-threatening or very disruptive to life, and only when there are no other reasonable therapies.
Despite its drawbacks, amiodarone truly is uniquely effective and has helped restore many thousands of people with disabling arrhythmias to a nearly normal life.
A Word From Verywell
When used appropriately, amiodarone can be a major benefit to people with severe cardiac arrhythmias. But because of its potential toxicity, its use should be limited.
Healthcare providers who prescribe amiodarone owe their patients a careful discussion of the many potential problems that can occur with the drug. Practitioners must commit to becoming long-term partners of their patients, carefully monitoring for new side effects for as long as this unique drug is being used.
