Rilzabrutinib in Antihistamine-Refractory Chronic Spontaneous Urticaria: The RILECSU Phase 2 Randomized Clinical...

Chronic spontaneous urticaria (CSU) is a skin disease driven mainly by the activation of cutaneous mast cells through various mechanisms. Bruton tyrosine kinase (BTK), expressed in B cells and mast cells, plays a critical role in multiple immune-mediated disease processes.

To determine the efficacy and risk profile of rilzabrutinib (SAR444671), an oral, reversible, covalent, next-generation BTK inhibitor, in treating patients with CSU.

The Rilzabrutinib Efficacy and Safety in CSU (RILECSU) randomized clinical trial was a 52-week phase 2 study comprising a 12-week, double-blind, placebo-controlled, dose-ranging period, followed by a 40-week open-label extension. The trial was conducted from November 24, 2021, through April 23, 2024. Fifty-one centers enrolled and randomized participants across 12 countries in Asia, Europe, North America, and South America. The trial participants included adults aged 18 to 80 years with moderate to severe CSU (weekly Urticaria Activity Score [UAS7] of 16 or more; weekly Itch Severity Score [ISS7] of 8 or more) not adequately controlled with H1-antihistamine treatment.

Patients were randomized 1:1:1:1 to rilzabrutinib, 400 mg, once every evening (400 mg/d), twice per day (800 mg/d), 3 times per day (1200 mg/d), or matching placebo.

The primary end point was change from baseline at week 12 in ISS7 (for US and US reference countries) or UAS7 (for non-US reference countries).

A total of 160 omalizumab-naive and omalizumab-incomplete responders were randomized (mean [SD] age, 44.1 [13.4] years; 112 [70.0%] female). The primary analysis population included only the 143 omalizumab-naive patients. Significant reductions at week 12 were observed with rilzabrutinib, 1200 mg/d, vs placebo from baseline in ISS7 (least squares [LS] mean, -9.21 vs -5.77; difference, -3.44 [95% CI, -6.25 to -0.62]; P = .02) and UAS7 (LS mean, -16.89 vs -10.14; difference, -6.75 [95% CI, -12.23 to -1.26]; P = .02). In addition, improvements in weekly Hives Severity Score (HSS7) and weekly Angioedema Activity Score (AAS7) were observed. Improvements in ISS7, UAS7, HSS7, and AAS7 were observed as early as week 1. CSU-related biomarkers, including soluble Mas-related G protein-coupled receptor X2, immunoglobulin (Ig)-G antithyroid peroxidase, IgG anti-Fc-ε receptor 1, and interleukin-31, were reduced compared to placebo at week 12. Rilzabrutinib demonstrated a favorable risk-benefit profile; adverse events occurring at a higher frequency with rilzabrutinib vs placebo included diarrhea, nausea, and headache.

The results of the RILECSU randomized clinical trial demonstrated efficacy and rapid onset of action of rilzabrutinib, 1200 mg/d, over 12 weeks, in addition to an acceptable adverse event profile. Together, these data support the use of rilzabrutinib in treating patients with moderate to severe CSU refractory to H1-antihistamines. Further research is needed to determine long-term efficacy and potential harms.

ClinicalTrials.gov Identifier: NCT05107115.