Amiodarone Lung Toxicity

Amiodarone (Cordarone, Pacerone) is the most effective drug yet developed for the treatment of cardiac arrhythmias. Unfortunately, it is also potentially the most toxic antiarrhythmic drug and the most challenging to use safely. Common side effects of amiodarone include thyroid disorders, corneal deposits which lead to visual disturbances, liver problems, bluish discoloration of the skin, and photosensitivity (easy sunburning).

Because of its potential to produce several kinds of toxicity, amiodarone should only be prescribed for people who have life-threatening or severely disabling arrhythmias, and who have no other good treatment options.

The most feared side effect of amiodarone, by far, is pulmonary (lung) toxicity.

What Is Amiodarone Lung Toxicity?

Amiodarone lung toxicity probably affects up to 5% of patients taking this drug. It is not known whether the lung problems caused by amiodarone are due to direct damage by the drug to the lung tissues, an immune reaction to the drug, or to some other mechanism. Amiodarone can cause numerous kinds of lung problems, but in most cases, the problem takes one of four forms. 

Acute Respiratory Distress Syndrome (ARDS)

The most dangerous type of amiodarone lung toxicity is a sudden, life-threatening, diffuse lung problem called acute respiratory distress syndrome (ARDS). With ARDS, damage occurs to the membranes of the lung’s air sacs, causing the sacs to fill with fluid, and greatly impairing the ability of the lungs to transfer sufficient oxygen into the bloodstream.

People who develop ARDS experience sudden, severe dyspnea (shortness of breath) and usually must be placed on mechanical ventilators. The mortality rate, even with intensive therapy, is quite high, approaching 50%.

Interstitial Pneumonitis

The most common form of amiodarone lung toxicity is a chronic, diffuse lung problem called interstitial pneumonitis (IP). In this condition, the air sacs of the lungs gradually accumulate fluid and various inflammatory cells, impairing the exchange of gasses in the lungs.

Usually, IP has an insidious and gradual onset, with slowly progressing dyspnea, cough, and rapid fatigue. Since many people taking amiodarone have a history of heart problems, the symptoms are easy to mistake for heart failure. For this reason, IP is often missed.

Pneumonia

Much less common are the "typical-pattern" types of pneumonia (also called organizing pneumonia) that are sometimes seen with amiodarone.

In this condition, the chest X-ray shows a localized area of congestion virtually identical to those seen with bacterial pneumonia. This form of amiodarone lung toxicity is easily mistaken for bacterial pneumonia—and treatment may be misdirected accordingly. It is usually when pneumonia fails to improve with antibiotics that the diagnosis of amiodarone lung toxicity is finally considered.

Pulmonary Mass

Rarely, amiodarone can produce a solitary pulmonary mass that is detected by a chest X-ray. The mass is most often thought to be a tumor or infection, and only when the biopsy is taken is amiodarone lung toxicity finally recognized.

How Amiodarone Lung Toxicity Is Diagnosed

There are no specific diagnostic tests that clinch the diagnosis, though there are strong clues that can be obtained by examining lung cells. These can be obtained from a biopsy or pulmonary lavage (flushing the airways with fluid), usually by means of a bronchoscopy. 

The key to diagnosing amiodarone lung toxicity, however, is to be alert to the possibility. For anybody taking amiodarone, lung toxicity needs to be strongly considered at the first sign of a problem. Unexplained pulmonary symptoms for which no other likely cause can be identified should be judged as probable amiodarone lung toxicity, and stopping the drug should be strongly considered.

Who's at Risk?

Anybody taking amiodarone is at risk for lung toxicity.

You may be at higher risk if you're:

• Taking higher doses (400 mg per day or more)
• Taking the drug for 6 months or longer
• Over 60 years old

Some evidence suggests that people with preexisting lung problems are also more likely to have pulmonary problems with amiodarone.

While monitoring with chest X-rays and pulmonary function tests often reveals changes attributable to the drug, few people with these changes go on to develop frank pulmonary toxicity. Although annual chest X-rays are often performed on people taking this drug, there is little evidence that such monitoring is useful in detecting those who eventually will develop overt pulmonary problems, or who ought to stop taking amiodarone because of a potential for lung toxicity.

Treatment of Amiodarone Lung Toxicity

There is no specific therapy that has been shown to be effective. The mainstay of treatment is stopping amiodarone.

Unfortunately, it takes many months to rid the body of amiodarone after the last dose. For most patients with the less severe forms of lung toxicity (IP, typical pneumonia, or a pulmonary mass), the lungs often eventually improve if the drug is stopped. Amiodarone should also be stopped for people who develop ARDS, but the damage might not be reversible in these cases.

High doses of steroids are most often given to treat amiodarone-induced ARDS, and while there are case reports of benefits from such therapy, it's unknown whether steroids actually make a significant difference. Steroids are also commonly used for all the other forms of amiodarone lung toxicity, but evidence that they are helpful in these conditions is sparse.

A Word From Verywell

Amiodarone lung toxicity is the most feared adverse effect of this drug, and pulmonary toxicity is unpredictable. It can be severe and even fatal. It can be a challenge to diagnose, and there is no specific therapy for it. Talk to your doctor about the risks, as well as the signs so you can seek medical attention immediately if you begin to develop pulmonary side effects.