Hills RJ, Ive FA.
DOI: 10.2340/0001555572438440

Many combinations of methotrexate and folic or folinic acid have been used to limit the side effects of methotrexate therapy in psoriasis or psoriatic arthropathy. Methotrexate inhibits the enzyme dihydrofolate reductase and prevents the formation of DNA and RNA. Folinic acid, the 5-formyl derivative of tetrahydrofolic acid, is the active form of folic acid. We have confirmed in 5 patients that continuous administration of folinic acid with weekly oral methotrexate prevents improvement of psoriasis. When folinic acid was ceased on the day of methotrexate in these patients their psoriasis improved. Five other patients with previous sensitivity to methotrexate, forcing cessation of therapy, were given weekly oral methotrexate and folinic acid every day except the day of methotrexate. Marked improvement of psoriasis or arthropathy occurred in each case without side effects. This method precisely limits the exposure to methotrexate, allowing a therapeutic effect without complication even in those patients who exhibit methotrexate sensitivity.