The ability of MTX to prolong drug survival was also suggested in psoriatic arthritis in several observational studies (26, 27, 52, 56). In a longitudinal observational study, the 1-year retention rate of anti-tumor necrosis factor alpha medications in patients with RA and PsA were 65.4% and 77.3%, respectively with concomitant MTX associated with a better drug survival (52). In this study, the combination with MTX was also associated with a crude 1-year survival of 85% in PsA versus 70% without concomitant MTX, p=0.02 (52). In the Danish biologics registry DANBIO, male sex, CRP level >10 mg/liter, concomitant methotrexate use, and low patient health visual analog scale score at baseline were associated with longer drug survival in PsA patients (27).