The goal of this research is to assess the percentage of non-responders to ≥ 2 NSAIDs candidates a biological therapy that could adequately respond to treatment with etoricoxib This study confirm the result of a previous study in a wider similar population. Basing on previous results, the response rate will be assessed by ASASBIO criteria. The efficacy of the treatment with etoricoxib 90 mg will be assessed at week 4 in a population of patients with AS who didn't respond adequately to a previous therapy with ≥ 2 NSAIDs.