Discriminant Capacity of Clinical Efficacy and Nonsteroidal Antiinflammatory Drug-sparing Endpoints, Alone or in Combination, in Axial Spondyloarthritis.

Objective: Using data from a randomized, double-blind, placebo-controlled study, we assessed the capacity of clinical and nonsteroidal antiinflammatory drug (NSAID)-sparing endpoints, alone and in combination, to discriminate between treatment effects in axial spondyloarthritis (axSpA).

Methods: Patients with active NSAID-resistant axSpA received etanercept (ETN) 50 mg/week or placebo for 8 weeks and tapered/discontinued NSAID. In posthoc logistic regression analyses, OR were calculated that indicated the capacity of the following endpoints to discriminate between the effects of ETN and placebo at Week 8: Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) 50; BASDAI ≤ 3; Assessment of Spondyloarthritis international Society (ASAS) 20; ASAS40; Ankylosing Spondylitis Disease Activity Score (ASDAS) with C-reactive protein (CRP) < 1.3 and ASDAS-CRP < 2.1; ≥ 50% decrease from baseline in ASAS-NSAID score, score < 10, and score = 0; and each clinical and/or each NSAID measure.

Results: In 90 randomized patients (ETN, n = 42; placebo, n = 48), disease activity was similar between groups at baseline: mean (± SD) BASDAI (ETN vs placebo) 6.0 ± 1.6 versus 5.9 ± 1.5. NSAID intake was high: ASAS-NSAID score 98.2 ± 39.0 versus 93.0 ± 23.4. OR ranged from 1.6 (95% CI 0.5-5.4) for ASDAS-CRP < 1.3 to 5.8 (95% CI 1.2-29.1) for BASDAI50 and NSAID score of 0; most measures (34/45) reached statistical significance (α = 0.05) favoring ETN. Most combined outcome variables using OR were more discriminant than single outcome measures.

Conclusion: These findings suggest that changes in NSAID intake during treatment do not prevent demonstration of clinically relevant effects of biologic treatment, and combined (i.e., clinical with NSAID-sparing) endpoints were frequently more discriminant than single (i.e., clinical) endpoints. ClinicalTrials.gov (NCT01298531).