Twelve patients with psoriasis have been treated with parenteral methotrexate at weekly intervals. Ten patients showed varying degrees of clinical improvement within six weeks, but two did not respond. In some cases, there was a dramatic fall in the mitotic activity of psoriatic epidermis at three and 24 hours after methotrexate, but the count rose again by the third day although in the patients who improved clinically the mitotic index did not return to the pretreatment level by seven days. In other cases there was a gradual fall in the mitotic count from the first to the seventh day. There was a marked fall in the mitotic index of the small intestinal epithelium after methotrexate, but unlike the psoriatic epidermis the mitotic count returned to the preinjection level by the seventh day. The results support the theory that the "healing" action of methotrexate in psoriasis is primarily a direct one on the premitotic and mitotic cells of the epidermis.
FRY L, McMINN RMH. Action of Methotrexate on Skin and Intestinal Epithelium in Psoriasis. Arch Dermatol. 1966;93(6):726–730. doi:10.1001/archderm.1966.01600240092019
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