Kiniksa Bets on Unproven Pericarditis Follow-On KPL-387 as ARCALYST Revenue Soars

Kiniksa Reports Strong Q2 ARCALYST Sales, Advances KPL-387 to Phase 3

Kiniksa Pharmaceuticals reported robust second-quarter 2026 financial results, with ARCALYST® (rilonacept) net product revenue reaching $243.6 million, representing approximately 55% year-over-year growth. This strong performance led the company to raise its 2026 ARCALYST net product revenue guidance to between $980 million and $995 million. In its clinical portfolio, Kiniksa announced positive interval analysis data from the KPL-387 Phase 2/3 trial in recurrent pericarditis, showing rapid and sustained reductions in pain and inflammation with a 300 mg SC once-monthly dose. Consequently, the pivotal Phase 3 PASTORALE trial for KPL-387 is now actively enrolling and dosing patients, with potential commercialization anticipated in 2028/2029. Additionally, the company is on track to initiate a Phase 1 trial for KPL-1161 by the end of 2026.

• Kiniksa's commercial product, ARCALYST, demonstrated strong financial performance in Q2 2026, generating $243.6 million in net product revenue, a substantial 55% increase year-over-year. This growth was attributed to increased new and repeat prescribers for recurrent pericarditis. As a result of this sustained momentum, Kiniksa has raised its full-year 2026 ARCALYST net sales guidance to a range of $980 million to $995 million, an increase from its previous guidance.
• The company announced positive Phase 2 data for KPL-387, an investigational IL-1R1 antagonist, in recurrent pericarditis. An interval analysis showed that the 300 mg SC once-monthly dose led to rapid and sustained reductions in Numeric Rating Scale (NRS) pain and inflammation, with a median time to treatment response of 4.0 days and C-Reactive Protein (CRP) normalization in 8.0 days. These compelling results supported the initiation of the pivotal Phase 3 PASTORALE trial, which is now enrolling and dosing patients.
• Kiniksa is actively advancing its pipeline, with the PASTORALE trial for KPL-387 evaluating a 300 mg SC once-monthly liquid formulation in up to approximately 85 participants with recurrent pericarditis, aiming for potential commercialization in 2028/2029. Furthermore, the company is progressing KPL-1161, an Fc-modified IL-1R1 antagonist designed for quarterly subcutaneous dosing, with plans to initiate a Phase 1 first-in-human clinical trial by the end of 2026, expanding its focus on cardiovascular indications.

KPL-387 PASTORALE Trial Design and Phase 2 Outcomes

The therapeutic landscape for recurrent pericarditis has been defined by key clinical trials evaluating targeted immunomodulatory agents and established anti-inflammatory treatments. The pivotal Phase 3 RHAPSODY trial and its long-term extension established the efficacy of the IL-1α/β inhibitor rilonacept. Other notable studies have assessed the IL-1 inhibitor anakinra, colchicine, and the investigational agent goflikicept.

| Trial / Analysis | Study Drug / Intervention | Key Design Parameters - - - - - - - - - - - - - - - - - - - -ja | Key Efficacy Outcomes - - - - - - - |
| RHAPSODY (Phase 3) | Rilonacept | Design: Double-blind, placebo-controlled, randomized-withdrawal trial in patients (≥12 years) with recurrent pericarditis.
Enrollment: N=61 were randomized 1:1 to rilonacept or placebo after a 12-week open-label run-in period where background medications were discontinued and patients achieved clinical response (CRP ≤0.5 mg/dL, NRS pain score ≤2.0). - - - - - - - | Primary Endpoint: Time to first adjudicated pericarditis recurrence.
• Significantly lower risk of recurrence vs. placebo (HR 0.04; P < 0.001).
• Recurrence rate: 7% (2/30) in the rilonacept group vs. 74% (23/31) in the placebo group.
• Patient-reported outcomes (PROs) significantly improved during the run-in period and were maintained with rilonacept treatment. - - - - - - - |
| RHAPSODY (Long-Term Ext.) | Rilonacept | Design: 24-month open-label extension (N=74).
Key Feature: An 18-month decision point where investigators opted to continue rilonacept, suspend for observation, or discontinue study participation. - - - - - - - | Key Outcomes:
• Annualized recurrence rate on rilonacept was 0.04 events/patient-year (vs. 4.4 pre-study).
• Risk of recurrence was reduced by 98% in patients who continued treatment vs. those who suspended it (HR 0.02; P<0.0001).
• 75% (6/8) of patients in the suspension group experienced a recurrence. - - - - - - - |
| AIRTRIP | Anakinra | Design: Randomized, placebo-controlled trial. - -- - - - - - - | Key Outcomes:
• Recurrence incidence was significantly reduced: 18.2% in the anakinra group vs. 90% in the placebo group.
• For patients who experienced a recurrence, the mean time to flare was 76.5 days for anakinra vs. 28.4 days for placebo.

Why New Options are Needed for Recurrent Pericarditis

Recurrent pericarditis (RP) remains a burdensome condition, marked by repeated hospitalizations, emergency visits, and treatment-related complications that erode patient quality of life. Despite the emergence of IL-1 blockade as a paradigm-shifting therapy, significant gaps persist in treatment standardization, mechanistic understanding, and equitable access — underscoring the need for continued innovation and targeted development across diverse patient populations.

• Lack of standardized treatment protocols: There is no universally accepted regimen for full-dose administration duration or tapering strategies across individual medications, leaving clinicians to rely on empirical, case-by-case decision-making rather than validated guidelines.

• Narrow therapeutic armamentarium: Available options remain limited to aspirin/NSAIDs, glucocorticoids, colchicine, and immunosuppressants (IL-1 blockers, azathioprine, IV immunoglobulins) — with over 10% of patients still experiencing recurrent symptoms despite colchicine plus conventional anti-inflammatory therapy.

• Need for individualized, mechanism-based care: Deeper insight into RP pathophysiology — spanning a continuum from autoinflammatory to mixed autoinflammatory/autoimmune phenotypes involving IL-1, IL-6, TNF-α, and JAK/STAT signaling — is needed to enable biomarker-driven, endotype-specific treatment selection.

• Access disparities in resource-limited settings: A real-world gap exists between genetic/mechanistic advances and practical accessibility to IL-1 inhibitors, particularly in low-resource and TB-endemic regions, where empirical anti-TB therapy is often unnecessarily prolonged due to an infection-centered rather than autoinflammatory diagnostic framework.

• Underserved high-risk subgroups: Patients with refractory or multiply recurrent disease, systemic immune-mediated disease (SID)-associated pericarditis, idiopathic recurrent pericarditis, and those excluded from pivotal trials (e.g., RHAPSODY) represent populations with distinct unmet needs requiring tailored therapeutic approaches.

• Risk of disease progression to constriction: Delayed recognition and late initiation of IL-1 inhibition may fail to halt progression to constrictive pericarditis, highlighting the need for earlier identification of high-risk patients and clarity on optimal timing of biologic intervention.

• Economic and comparative evidence gaps: Pharmacoeconomic data for newer agents such as rilonacept remain scarce — particularly in newly recognized markets (e.g., China, where RP was designated a rare disease in 2023) — limiting full definition of their role and value within the RP treatment paradigm.

Kiniksa's IL-1 Pathway Strategy in Recurrent Pericarditis

In addition to rilonacept, several other IL-1 inhibitors are being investigated for recurrent pericarditis, employing a similar mechanism of action. Competitors including anakinra, canakinumab, and goflikicept have been evaluated in clinical trials with varying intervention models to establish efficacy and safety in this indication. The table below outlines these other IL-1 inhibitors and their respective trial designs for treating recurrent pericarditis.