Clinical Characteristics and Predictors of Primary Non-Response to Biologic Therapy in Rheumatoid Arthritis and Axial Spondyloarthritis.

Aim: According to EULAR treat-to-target recommendations, biologic (bDMARD) and targeted synthetic (tsDMARD) therapies are recommended for patients with rheumatoid arthritis (RA) and axial spondyloarthritis (axSpA) who have an inadequate response to conventional treatment. However, some patients either fail to achieve the desired response (primary non-response) or lose efficacy over time (secondary non-response). This study aimed to determine the rates and predictors of primary non-response to bDMARD/tsDMARDs in RA and axSpA. Methods: This was a retrospective study including RA and axSpA patients who received bDMARD/tsDMARD therapy at X University between January 2017 and March 2025. Primary non-response was defined as no clinical improvement within six months of treatment initiation, and secondary non-response as loss of initial response within 6-12 months (early) or after 12 months (late). Statistical analyses were performed using SPSS 23.0. Results: A total of 495 patients (167 RA, 328 axSpA) were analysed. Primary non-response was higher in RA (45.1%) than axSpA (15.9%), as was secondary non-response (80.4% vs. 39.3%, p<0.001). In RA, longer disease duration was independently associated with primary non-response (OR 1.054, 95% CI 1.008- 1.102; p = 0.021). In axSpA patients, higher BMI was independently associated with primary non-response (OR 1.079; 95% CI 1.025-1.136; p = 0.004). No other demographic or clinical variables remained significantly associated with primary non-response after multivariable adjustment in either group. Conclusion: Longer disease duration in RA and higher BMI in axSpA were independent predictors of primary non-response, highlighting the importance of early treatment in RA and metabolic considerations in axSpA.