Head-to-Head Trial Finds Stronger Joint Response With Bimekizumab

New topline results from the phase 3 BE BOLD trial suggest that the dual interleukin-17 inhibitor bimekizumab (Bimzelx; UCB) may provide greater improvement in joint symptoms than the interleukin-23 inhibitor risankizumab (Skyrizi; AbbVie) in adults with active psoriatic arthritis (PsA). The randomized study met its primary endpoint, demonstrating statistically significant superiority of bimekizumab in achieving an ACR50 response at week 16, a relatively stringent measure of clinical improvement.¹

The findings were announced by UCB, the developer of bimekizumab, and add to a growing body of head-to-head evidence evaluating biologic therapies across immune-mediated inflammatory diseases.

Psoriatic Arthritis and the Need for Effective Therapies

PsA is a chronic inflammatory condition affecting both the musculoskeletal system and the skin. Although prevalence estimates vary globally, the disease affects roughly 0.02% to 0.25% of the population. Among individuals with psoriasis, up to 30% may eventually develop PsA.²

Because of the heterogeneity of the condition, treatment strategies often require individualized approaches. Biologic therapies targeting key inflammatory pathways—including tumor necrosis factor (TNF), IL-17, and IL-23—have become central to disease management in patients who do not respond adequately to conventional disease-modifying antirheumatic drugs (DMARDs).

Trial Design: BE BOLD

The BE BOLD trial was designed to directly compare the efficacy and safety of bimekizumab and risankizumab in adults with active PsA.

In this multicenter, randomized, double-blind, parallel-group study, 553 participants were assigned in a 1:1 ratio to receive either bimekizumab or risankizumab. Eligible participants included patients who were biologic-naïve or who had previously received one tumor necrosis factor inhibitor but experienced inadequate response or intolerance.

The study’s primary endpoint was the proportion of patients achieving ACR50 at week 16. This outcome measure requires at least a 50% improvement in tender and swollen joint counts along with similar improvement in multiple additional parameters, including physician and patient global assessments, pain, functional status, and inflammatory markers such as C-reactive protein. Compared with ACR20—commonly used in many trials—ACR50 is generally considered a more demanding threshold of clinical response.

Key Topline Findings

According to the topline results, treatment with bimekizumab resulted in a statistically significant improvement in ACR50 response rates at week 16 compared with risankizumab. While detailed response percentages and subgroup analyses have not yet been publicly released, researchers reported that the primary endpoint was met with superiority.

From a safety perspective, bimekizumab was generally well tolerated, and no new safety signals were identified through the 16-week analysis period. Longer-term safety outcomes will likely become clearer when full data from the study are presented and published.

The trial remains double-blinded through week 24, and further analyses are expected to include additional clinical outcomes relevant to PsA, such as skin response, enthesitis resolution, physical function, and patient-reported outcomes.

Mechanistic Considerations

Bimekizumab is a humanized monoclonal IgG1 antibody designed to selectively inhibit both IL-17A and IL-17F, cytokines that play key roles in inflammatory signaling. Most currently available IL-17–targeted therapies focus on IL-17A alone. Dual inhibition of IL-17A and IL-17F may offer broader suppression of inflammatory pathways implicated in psoriatic disease.

In contrast, risankizumab targets the IL-23 pathway by selectively binding to the p19 subunit of the cytokine. IL-23 inhibition has shown strong efficacy in psoriasis and has demonstrated benefits in PsA as well, though the pathways targeted differ from IL-17–focused therapies.

Head-to-head trials between biologic classes remain relatively uncommon in rheumatology and dermatology, making comparative studies such as BE BOLD potentially informative for treatment selection.

Clinical Context

Bimekizumab is already approved in several regions for multiple inflammatory conditions, including moderate to severe plaque psoriasis and PsA. It has also been approved in Europe for axial spondyloarthritis and hidradenitis suppurativa.

The BE BOLD results represent the fourth reported head-to-head study in which bimekizumab demonstrated superiority versus another biologic therapy. For clinicians managing PsA, such comparative trials may help clarify differences in efficacy among biologic classes, particularly when choosing therapies after inadequate response to conventional DMARDs or TNF inhibitors.

What Comes Next

Full efficacy and safety results from BE BOLD are expected to be presented at a future international medical congress and submitted for peer-reviewed publication. These forthcoming analyses will likely provide greater detail on response rates, subgroup outcomes, and longer-term safety.

For clinicians treating psoriatic arthritis, the study highlights a continuing shift toward direct comparative evidence among targeted therapies—an approach that may help refine treatment strategies in a disease where both joint and skin manifestations must often be addressed simultaneously.

References

1. BIMZELX[®]▼(bimekizumab) superior to SKYRIZI[®] (risankizumab) in BE BOLD: first head-to-head study in active psoriatic arthritis (PsA) to demonstrate superiority in ACR50. News release. UCB. Published March 11, 2026. Accessed March 11, 2026. https://www.ucb.com/newsroom/press-releases/article/bimzelxrvbimekizumab-superior-to-skyrizir-risankizumab-in-be-bold-first-head-to-head-study-in-active-psoriatic-arthritis-psa-to-demonstrate-superiority-in-acr50
2. Lembke S, Macfarlane GJ, Jones GT. The worldwide prevalence of psoriatic arthritis-a systematic review and meta-analysis. Rheumatology (Oxford). 2024;63(12):3211-3220. doi:10.1093/rheumatology/keae198