Insmed Delivers Rare Disappointment as Brinsupri Flops in Mid-Stage Rhinosinusitis Study
Insmed reported that its DPP1 inhibitor brensocatib (Brinsupri) failed a Phase 2/2b mid‑stage study in patients with chronic rhinosinusitis without nasal polyps, showing no efficacy benefit at either of two tested doses versus placebo in reducing nasal inflammation or symptoms.1234
The setback breaks a recent “win streak” for Insmed, which had seen strong data in bronchiectasis in May 2024 and subsequently gained regulatory approval of Brinsupri in August 2025 for non‑cystic fibrosis bronchiectasis, where it is already commercially available.1
Following the rhinosinusitis trial failure announcement, Insmed’s share price dropped roughly 17–20% in late Wednesday/early Thursday trading, erasing part of a steep run‑up that had recently taken the stock above $200 per share.134
Insmed is ending development of brensocatib/Brinsupri in chronic rhinosinusitis, with analysts noting that this indication was always a high‑risk, proof‑of‑concept bet due to the lack of reliable animal models for the disease.13
Despite the nasal study flop, analysts such as RBC Capital Markets’ Leonid Timashev maintain a positive broader outlook, projecting ~$700 million in Brinsupri sales in 2026 from its approved bronchiectasis indication and continued contributions from Insmed’s other marketed drug Arikayce.1
Insmed attempted to offset the negative news by announcing the acquisition of INS1148, a monoclonal antibody ready for Phase 2 trials targeting respiratory, immunologic, and inflammatory diseases, with initial studies planned in interstitial lung disease and moderate‑to‑severe asthma.14
Analysts report that Insmed paid about $40 million upfront to privately held Opsidio for INS1148, plus potential development, commercial milestones, and royalties, signaling continued investment in its inflammation and respiratory pipeline despite the Brinsupri rhinosinusitis failure.1
The failed rhinosinusitis trial is viewed more as a setback for pipeline expansion than a threat to the core investment thesis, as it does not affect Brinsupri’s existing bronchiectasis approval or ongoing development in other indications such as hidradenitis suppurativa.13
Sources:
1. https://www.biopharmadive.com/news/insmed-brensocatib-birch-rhinosinusitis-study-results/808251/
2. https://www.statnews.com/2025/12/18/biotech-news-insmed-nasal-inflammation-trial-flops/
3. https://firstwordpharma.com/story/6774073
4. https://www.tradingview.com/news/zacks:5e008e711094b:0-insm-stock-plummets-on-sinus-study-failure-adds-new-pipeline-asset/