Abstract
BACKGROUND: Ankylosing spondylitis (AS) is a form of rheumatic disease caused by chronic inflammation of the axial skeleton. Patients with AS experience significant functional limitations and reduced quality of life. Consequently, AS imposes a substantial economic burden on society due to productivity loss and work disability. Biologics, including tumor necrosis factor (TNF) inhibitors and human anti-interleukin-17A monoclonal antibody (IL-17A) agents, are effective treatment strategies in relieving symptoms and slowing down disease progression. Currently, 5 TNF inhibitors and 2 IL-17A antibody agents are approved by the FDA for the management of AS. Of these agents, there is no clear preferred agent in initial biologic therapy, although an IL-17A antibody agent or alternative TNF inhibitor agent is recommended after failure of the initial TNF inhibitor therapy. OBJECTIVE: To assess cost-effectiveness of treatment strategies with biologics, TNF inhibitor or IL-17A, in accordance with the treatment guidelines for patients with AS. METHODS: An economic patient-level simulation combining decision-tree and Markov models was constructed from the U.S. health care payer's perspective over a 10-year time horizon. The current model examined 5 treatment strategies: (1) conventional care treatment with nonsteroidal anti-inflammatory drugs, (2) 1 TNF inhibitor, (3) an IL-17A antibody agent, (4) sequential therapy with 2 TNF inhibitors, and (5) sequential therapy with a TNF inhibitor followed by an IL-17A antibody agent. Initially, treatment responses were determined after 12-week treatments. Patients who responded to treatment entered a "responders" Markov model. Patients entered a "nonresponders" Markov model if they inadequately responded to treatment. In sequential treatment strategies, patients who inadequately responded to treatment with the first TNF inhibitor received a second TNF inhibitor or an IL-17A antibody agent. Health utility was estimated based on the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Functional Index (BASFI) scores. The models accounted for real-world adherence to TNF inhibitor treatment. Scenario and probabilistic sensitivity analyses were performed to test the robustness and uncertainty of the model results. RESULTS: Over a 10-year time horizon and 100,000 simulated patients for each treatment strategy, base-case results produced average total discounted per-patient costs of $19,765, $130,302, $159,934, $190,553, and $179,118 and quality-adjusted life-years (QALYs) of 4.675, 5.410, 5.499, 5.919, and 5.893 for conventional care, treatment strategies with 1 TNF inhibitor, an IL-17A, 2 TNF inhibitors, and a TNF inhibitor followed by an IL-17A, respectively. The optimal treatments at willingness-to-pay (WTP) thresholds ≤ $130,813 per QALY, between $130,813 per QALY and $442,728 per QALY, and > $442,728 per QALY were conventional care and sequential treatment strategies with 1 TNF inhibitor, followed by an IL-17A agent and 2 TNF inhibitors, respectively. CONCLUSIONS: Study findings suggested that all treatment strategies with biologics, TNF inhibitors or IL-17A antibody agents, in the treatment guidelines for AS were not cost-effective at the common WTP of $100,000 per QALY. However, the sequential treatment with 1 TNF inhibitor followed by an IL-17A antibody agent was considered cost-effective at a higher WTP of $150,000 per QALY. DISCLOSURES: No outside funding supported this study. The authors have nothing to disclose. Primary findings of this study were presented in part at the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) in Baltimore, MD, May 2018.