Insmed shares fell ~20% after its 1Q2026 earnings call despite reporting $207.9 million in Brinsupri revenue, ahead of VA consensus of $198 million. The market reaction was partly driven by management’s commentary that early launch momentum had benefited from a pool of “ready-and-waiting” patients built up ahead of approval. Investors also appeared to question whether Insmed’s stated Brinsupri persistence was strong enough to support continued growth as new patient additions normalized, despite management confidently reiterating its guidance of $1 billion in 2026.
Consumer Edge has unique insight into Brinsupri utilization data through Phoenix, a closed-claims dataset. The data supports the view that launch demand was front-loaded, but also shows that returning patients are increasingly driving prescription growth.
The “ready-and-waiting” dynamic is clearly visible in Phoenix data. Weekly new-to-brand prescriptions spiked in 4Q2025, consistent with providers working through a backlog of interested patients shortly after approval. Since then, new starts have settled into a steadier range, with volumes trending lower in recent months. At the same time, Brinsupri’s prescription mix has shifted sharply toward returning patients, with refills surpassing new-to-brand fills by November 2025 and now accounting for more than 90% of weekly volume.
This points to generally strong Brinsupri persistence. On the earnings call, management cited drugs such as generic statins as retaining ~70% of patients at six months and said Brinsupri was tracking “slightly above” that level. While statins are not clinically comparable to Brinsupri, they offer a familiar benchmark for persistence in chronic oral therapy given their broad use and well-studied adherence. The Phoenix data broadly corroborates this, where we see Brinsupri persistence is ~70% at 6 months, though we see atorvastatin and rosuvastatin persistence slightly higher, at ~80%. While the commentary appeared to contribute to a negative market reaction, the Phoenix data suggests persistent Brinsupri patients are contributing meaningfully to transaction growth.
The key forward-looking question is whether growth from persistent returning patients can continue to offset a smaller, more stable base of new starts. Early launch demand has clearly normalized, but refill volume is now the dominant driver of total prescriptions. If Brinsupri maintains current persistence levels, total volume can continue to grow even as new patient additions moderate, though the pace of growth will increasingly depend on sustaining adherence and broadening the new patient funnel beyond the initial backlog.
Notes: Analysis based on Consumer Edge Phoenix closed-claims data, normalized to a 2023 patient enrollment panel. Statin comparison is an imperfect analog cited for persistence context only; patient population, access dynamics, and out-of-pocket costs differ from Brinsupri.
