Impact of methotrexate therapy on the folate status of psoriatic patients

Folate status was assessed in 20 patients with psoriasis on long‐term methotrexate therapy and in 17 psoriatics not receiving methotrexate or any other systemic treatment. In the long‐term treated group the erythrocyte folate concentration was significantly lower (P < 0.01) (reflecting low polyglutamate storage) and the plasma concentration of oxidized folate forms (pteroylgluta‐mate and dihydrofolate) was significantly higher (P < 0.005) (reflecting decreased dihydrofolate reductase activity) than in the control group. The values of haemoglobin, mean cellular volume, aspartate aminotransferase and alkaline phosphatase did not differ statistically significantly in the two groups. The study shows that there is a potential for an intracellular folate depletion during long‐term methotrexate therapy.