Will BRINSUPRI's gross-to-net adjustment remain below 35% through FY2026?

Management guided GTN at mid-20s to low 30s. First-in-class monopoly drugs in rare disease typically maintain lower GTN than mass-market drugs for 2-3 years post-launch. BRINSUPRI has no approved alternative, giving Insmed strong payer negotiating leverage. The 35% threshold is at the upper end of guidance — management would need to be significantly wrong about payer dynamics for GTN to exceed this level. Historical rare disease GTN trajectories support staying below 35% in the first full year.

The primary risk to GTN exceeding 35% would be a shift in payer mix toward Medicaid/340B patients as coverage expands to lower-income populations. As more patients gain access, the proportion covered by government programs may increase, mechanically raising GTN. However, bronchiectasis patient demographics skew older (Medicare) rather than lower-income (Medicaid), limiting this risk. The 35% threshold provides meaningful buffer above the guided range.

Insmed has existing GTN experience with ARIKAYCE, providing internal benchmarking. The ARIKAYCE GTN trajectory informs BRINSUPRI contracting strategy. Management's guidance of mid-20s to low 30s likely reflects actual contracted rates with major PBMs. Exceeding 35% would require unanticipated payer actions (prior auth denials forcing co-pay assistance, mandatory rebate increases) that are unlikely in the first full year of a rare disease monopoly drug.

Specialty pharma GTN has trended upward 1-2pp annually industry-wide, but BRINSUPRI's monopoly status provides insulation. The 35% threshold is generous relative to the guided range. The most likely GTN outcome for FY2026 is 28-32%, well below the 35% resolution threshold. Probability of staying below 35% is meaningfully above coin-flip.

The question is essentially asking whether management's GTN guidance is directionally correct. Management has strong visibility into contracted rates and there's no structural reason to expect a >5pp miss to the upside. First-in-class rare disease drugs in their first full year almost never exceed 35% GTN.

A modest discount from the strong base case to account for tail risks: unexpected state-level pricing regulation, a surprise Medicaid coverage mandate that increases rebate exposure, or aggressive pharmacy benefit manager renegotiations. These are low-probability events but would directly impact GTN. The 62% probability reflects 70%+ base case minus tail risk discount.

Monopoly pricing power plus management guidance well below 35% makes this a clearly favorable probability. Rare disease GTN patterns support staying below threshold. 70% probability.

First-in-class status and management guidance of mid-20s to low 30s provide strong buffer below 35%. The full-year time horizon and payer mix evolution create some risk. Probability above 60%.

The combination of monopoly status, management guidance, and rare disease GTN patterns creates a clear favorable probability. Only significant regulatory or payer disruption would breach 35%. Probability in mid-to-high 60s.