The combination of anti TNF alpha and MTX was also retrospectively assessed in observational studies. Most of them suggest that the systematic combination of MTX to biologic since the anti TNF alpha initiation improve survival rate of biologics (21, 24, 29, 30, 31). A retrospective cohort study including 93 patients treated with infliximab for psoriasis showed that concomitant MTX at an average weekly dose of dose of 7.5 to 17.5 mg of MTX enhanced the maintenance of response and prolonged drug survival (by a mean ± SD of 19.5 ± 8.1 months, P = 0.034) (23). In addition, time until first infliximab dose escalation was delayed in patients receiving MTX (by a mean ± SD of 12.0 ± 6.1 months, P =0 .037). In the same study, after 2 years of treatment, 25% of patients without MTX were still under the initial infliximab regimen versus 40% of patients receiving a combination of infliximab with MTX (30).