Methotrexate is an antimetabolite that interferes with DNA synthesis, repair, and cellular replication by inhibiting dihydrofolate reductase. Dihydrofolate reductase reduces folic acid to tetrahydrofolic acid, which is a carrier of one-carbon groups in the synthesis of purine nucleotides and thymidylate. In general, actively proliferating tissues are more sensitive to the effect of methotrexate. In rheumatoid arthritis, the methotrexate mechanism of action is unknown, but it may have an effect on immune function [3][4]. Methotrexate controls the psoriasis process of increased proliferation in the rate of epithelial cell production in the skin