Smoking history and underlying lung disease are associated with poor outcome in patients developing interstitial pneumonia during low‐dose amiodarone therapy

Background Amiodarone is a useful antiarrhythmic drug, especially in patients with serious heart diseases, but amiodarone‐induced interstitial pneumonia (AMD‐IP) is sometimes lethal. Methods and results We retrospectively analyzed the clinical characteristics of 280 patients who were treated with daily oral amiodarone. Among the patients, 29 (10.2%) developed AMD‐IP during the follow‐up period of 66.0±38.2 months. The average dose of amiodarone in the AMD‐IP group (173±10 mg) was significantly higher than that in the non‐AMD‐IP group (150±3 mg). The prevalence of smoking history (AMD‐IP group: 70.0%; non‐AMD‐IP group: 42.2%; P <0.01) and underlying lung disease (AMD‐IP group: 17.2%; non‐AMD‐IP group: 5.6%; P <0.05) was significantly higher in the AMD‐IP group than in the non‐AMD‐IP group. Furthermore, multiple stepwise logistic regression analysis demonstrated that smoking history was an independent predictor of AMD‐IP (OR, 3.56; 95% CI, 1.08–10.23; P <0.001). Among patients who developed AMD‐IP, those with chronic obstructive pulmonary disease (COPD) had a higher relapse rate and a worse prognosis. Conclusions During the mean follow‐up period of >5 years, 10.2% of patients receiving low‐dose amiodarone therapy developed AMD‐IP. Higher maintenance doses, smoking history, and preexisting lung disease were related to the development of AMD‐IP. The AMD‐IP patients with COPD had a poor prognosis.