Axial spondyloarthritis is a chronic inflammatory disease that causes severe pain and disability.

The biologic agents TNFα inhibitors (TNFi) and anti-interleukin (IL)-17A antibodies have demonstrated efficacy to reduce disease activity and risk of progression, but some patients experiment lack (primary treatment failure) or loss (secondary treatment failure) of response.

As the definition of treatment failure is often vague, here we propose a definition based on loss of the following status: low disease activity according to Ankylosing Spondylitis Disease Activity Score (ASDAS)-CRP, absence of extra-articular manifestations, and low disease impact on the patients’ general health.

Physicians should carefully consider the moment and the reason for the treatment failure to decide the next therapeutic step. The main options are targeting the same biologic pathway (changing between TNFi) or switching to another class of drug (anti-IL-17).