Dec 17 (Reuters) - Insmed said on Wednesday it had discontinued the development of its experimental anti-inflammatory drug to treat a chronic sinus condition after it failed to show benefit in a mid-stage study, sending its shares down nearly 19% in extended trading.

The drug, brensocatib, failed to meet the main goal of improving sinus-related symptoms such as nasal congestion in patients with chronic rhinosinusitis without nasal polyps, an inflammatory condition of the sinuses.

Brensocatib, branded as Brinsupri, is approved in the U.S. to treat non-cystic fibrosis bronchiectasis, a chronic lung condition characterized by permanently damaged airways.

The mid-stage study tested two doses of brensocatib against a placebo in 288 patients for 24 weeks in addition to a nasal spray treatment to relieve symptoms.

The drug was generally safe, with no new safety signals, the company said, adding that it plans to present these data at a future meeting.

Insmed also announced it had acquired a new experimental antibody, INS1148, which it plans to develop for lung and immune diseases such as interstitial lung disease and moderate-to-severe asthma.