Lilly's Combination Therapy Shows Superior Efficacy in First-of-Kind Trial for Psoriatic Arthritis Patients with Obesity
Key Insights
Eli Lilly's TOGETHER-PsA Phase 3b trial demonstrated that combining Taltz (ixekizumab) with Zepbound (tirzepatide) achieved superior outcomes compared to Taltz monotherapy in patients with active psoriatic arthritis (search) and obesity (search) or overweight.
The combination therapy met the primary endpoint with 31.7% of patients achieving both ACR50 response and ≥10% weight reduction at 36 weeks, compared to just 0.8% on Taltz alone (p<.001).
This represents the first controlled study to evaluate an incretin therapy with a psoriatic arthritis (search) biologic, potentially establishing a new paradigm for integrated treatment of these commonly co-occurring conditions.
Eli Lilly and Company announced positive topline results from the groundbreaking TOGETHER-PsA Phase 3b trial, demonstrating that the combination of Taltz (ixekizumab) and Zepbound (tirzepatide) delivered superior efficacy compared to Taltz monotherapy in adults with active psoriatic arthritis (search) and obesity (search) or overweight. The 36-week results mark a significant milestone as the first controlled study to evaluate an incretin therapy used with a psoriatic arthritis biologic.
Primary Endpoint Achievement
The combination therapy met its primary endpoint with remarkable efficacy. At 36 weeks, 31.7% of patients in the Taltz plus Zepbound treatment arm achieved both a 50% improvement in psoriatic arthritis (search) activity based on American College of Rheumatology 50 (ACR50) criteria and weight reduction of at least 10%, compared to just 0.8% of patients on Taltz monotherapy (p<.001).
In a key secondary endpoint, the combination delivered a 64% relative increase over Taltz monotherapy in the proportion of patients who achieved ACR50 response (33.5% versus 20.4%, respectively, p<.05). This finding demonstrates that treatment of obesity (search) or overweight with Zepbound reduced the burden of psoriatic arthritis (search).
Clinical Significance and Patient Population
The study addressed a significant unmet medical need, as an estimated 65% of adults with psoriatic arthritis (search) in the U.S. also have obesity (search) (BMI ≥30 kg/m²) or overweight (BMI 27-29.9 kg/m²) with at least one additional weight-related comorbidity. The trial enrolled a challenging patient population with high disease burden at baseline and an average BMI of 37.6 kg/m² across both treatment arms. Patients demonstrated high disease activity and meaningful functional impairment, with more than 60% having prior experience with one or more advanced therapies.
"TOGETHER-PsA represents a pioneering first step leveraging Lilly's leadership in incretin science to deliver a major advance in disease outcomes for people living with the cumulative burden of psoriatic arthritis (search) and obesity (search) or overweight," said Mark Genovese, M.D., senior vice president of Lilly Immunology development. "This is the first controlled pharmacologic study to demonstrate that treatment of obesity improved PsA disease measures."
Safety Profile
Adverse events in participants treated with the combination therapy were generally mild to moderate, consistent with the known safety profiles of each medicine. The most common adverse events occurring in ≥5% of participants were nausea, diarrhea, constipation, and injection site reactions in the combination treatment arm, compared to injection site reactions and upper respiratory tract infections in the Taltz monotherapy arm.
Expert Perspective on Treatment Paradigm
Joseph F. Merola, M.D., Professor and Chair of the Department of Dermatology and Professor of Internal Medicine in the Division of Rheumatic Diseases at UT Southwestern Medical Center, emphasized the clinical significance of these findings. "While treatment guidelines for psoriatic arthritis (search) recommend management of obesity (search), the reality is these two chronic diseases are often addressed separately and moving the needle in psoriatic arthritis has remained challenging," he said. "The observed benefit with treatment using Taltz and Zepbound appears to meaningfully impact psoriatic disease activity, indicating that for many patients, PsA is an obesity-related condition."
Study Design and Methodology
TOGETHER-PsA (NCT06588296) is a 52-week Phase 3b, randomized, multicenter, assessor-blinded, open-label study. A total of 271 participants were randomized 1:1 to receive either Taltz alone or concomitantly with Zepbound, both administered subcutaneously. Patients in both arms received counseling on a reduced-calorie diet and increased physical activity. Participants were required to have a BMI ≥30 kg/m², or ≥27 to <30 kg/m² with at least one weight-related comorbidity.
Mechanism of Action
Taltz is a monoclonal antibody that selectively binds with interleukin 17A (search) (IL-17A) cytokine and inhibits its interaction with the IL-17 receptor, thereby inhibiting the release of pro-inflammatory cytokines and chemokines. Zepbound is the only FDA-approved dual GIP (search) (glucose-dependent insulinotropic polypeptide) and GLP-1 (search) (glucagon-like peptide-1) receptor agonist obesity (search) management medication, which lowers body weight by decreasing calorie intake and appetite.
Future Developments
Detailed 36-week results from the TOGETHER-PsA trial will be presented at an upcoming medical meeting and discussed with regulators. Additionally, topline results from the ongoing TOGETHER-PsO trial, investigating the efficacy and safety of treating adults with moderate-to-severe plaque psoriasis and obesity (search) or overweight with the combination therapy compared to Taltz monotherapy, are expected in the first half of 2026.
With these results, Taltz becomes the first and only biologic for psoriatic arthritis (search) with data supporting a potential comprehensive treatment approach alongside an incretin therapy for patients who also have obesity (search) or overweight with at least one weight-related condition.