This study highlights data from two existing clinical trials to capture PASI 50 and PASI 75 responder rates which represent a common metric used in current psoriasis clinical trials. In study A 3. a multicenter Canadian trial, a total of 63 patients (42 men, 21 women) with severe psoriasis were enrolled. A 12 month treatment of severe psoriasis with acitretin: results of a Canadian open multicenter study. Received 20 July 2001; Accepted 12 October 2001. Etretinate was the first synthetic retinoid used in the therapy of psoriasis. Over the subsequent 2 months his symptoms improved and his liver tests normalized. A 12-month treatment of severe proriasis with acitretin: Results of a Canadian open multicenter study. R.K., Ross, J.B., Stewart, W.D. et al, A 12-month treatment of severe psoriasis with acitretin: results of a Canadian open multicenter study. J Am Acad Dermatol.