Which medication is most likely causing a patient’s interstitial lung disease and dyspnea on exertion?

Nitrofurantoin is known for its potential to induce pulmonary complications, including interstitial lung disease. This medication is often used as an antibiotic for urinary tract infections, and while generally well-tolerated, it has been associated with both acute and chronic pulmonary toxicity.

In particular, chronic use can lead to a condition often referred to as nitrofurantoin-induced pulmonary fibrosis, which can manifest as interstitial lung disease. Symptoms such as dyspnea on exertion may occur as the lung tissue becomes increasingly damaged, leading to impaired gas exchange.

The other options do not typically cause interstitial lung disease. Ciprofloxacin, although an antibiotic, is not known for significant pulmonary toxicity. Amiodarone, while it can cause pulmonary toxicity as well, is less common compared to nitrofurantoin with respect to interstitial lung disease development. Beta-blockers generally have cardiovascular effects and do not directly induce lung pathology like interstitial lung disease. Therefore, nitrofurantoin is the most likely medication among the choices provided to cause the described symptoms.