Methotrexate in erythrocytes of patients with psoriasis

Methotrexate (MTX) concentrations in erythrocytes in 32 psoriatics treated weekly with MTX p.o. or i.m. have been studied. When treatment had been constant for at least 5 weeks, there was only small variation in erythrocyte MTX (ery-MTX) in the week between two courses of treatment. The ery-MTX was correlated with the weekly dose of MTX. For patients treated with MTX i.m. r = 0.87, and in patients given divided oral doses r was 0.68. There was no difference in ery-MTX between the two routes of administration. No correlation was observed between ery-MTX and the total MTX dose or the length of treatment. During constant MTX administration small variations in ery-MTX were observed. Small changes in the weekly dose of MTX resulted in marked changes in ery-MTX in 4 of the 5 patients studied.