Methotrexate (MTX) interferes with the normal metabolism of folate, a B vitamin. It inhibits the growth of cells. Cells that grow rapidly, such as skin cells in psoriasis, are more susceptible to MTX than normal cells.
A major drawback to the use of methotrexate is that users must undergo a liver biopsy every few years (after each 1,500 mg total cumulative dose) to check for liver disease (cirrhosis). The real and perceived risks of this procedure have been a factor in the success of the newer biologic drugs, which do not share this requirement.
Methotrexate is recommended for those who have psoriasis over a good portion of their body. It should be used when other treatments, such as phototherapy or acetretin, have already failed. It is also a very effective drug against psoriatic arthritis. In these instances, MTX can be considered a first-line treatment choice.
Methotrexate is a very effective weapon against difficult psoriasis, such as exfoliative erythroderma (where the entire body turns red) and generalized pustular psoriasis.
Methotrexate should be avoided or used with extreme caution in patients with current or planned pregnancy, alcoholism, hepatitis, cirrhosis, renal failure, immunodeficiency and blood disorders.
Methotrexate is a relatively toxic drug, and care must be taken to monitor for problems, such as oral ulcerations, bone marrow suppression, lymphoma, birth defects, sun sensitivity, and lung, liver, and kidney toxicity. The more serious of these, however, are relatively rare with the low doses of methotrexate used to treat psoriasis.
Source: Camisa C. Handbook of Psoriasis, 2nd Ed. Blackwell Publishing, USA 2004.
