Psoriasis – Methotrexate

March 28th, 2011

Methotrexate is a systemic medicine FDA approved for the treatment of severe Psoriasis and has efficacy in the treatment of Psoriatic arthritis and I occasionally manage and prescribe this medicine in both my The Woodlands dermatology and Conroe dermatology offices.  Methotrexate is usually prescribed in pill form which is taken once a week.  There is a subcutaneous injectable form in patients who are on doses over 20mg per week or who cannot tolerate the pills.  Methotrexate functions in Psoriasis by binding to and inhibiting an enzyme that causes the rapid proliferation of skin cells.  Methotrexate is very effective but does have serious side effects.  Patients who should not take Methotrexate include alcoholics, patients with cirrhosis of the liver, patients with immunodeficiency, patients with an infectious disease, patients with bone marrow defects, patients who are pregnant/breastfeeding/attempting to conceive, and patients with renal insufficiency.  Both men and women should not conceive while taking Methotrexate as it can cause serious birth defects. Men must be off Methotrexate for 3 months prior to attempting to conceive and women must have stopped the medicine for at least 4 months.  Liver damage is a major concern for patients on Methotrexate.  Liver biopsies must be obtained at certain intervals while on Methotrexate to monitor for liver damage.  Lung damage can occur on Methotrexate in which patients may have an acute toxicity or a chronic fibrosis may develop.  Bone marrow suppression may arise resulting in low levels of red blood cells, white blood cells, and platelets.  Thus, cell blood counts are obtained weekly for the first month then every month for three months then every 3 months.  Some patients have GI intolerance such as abdominal pain, diarrhea, mouth ulcers so daily supplementation with folic acid is recommended to reduce these symptoms.  Patients on Methotrexate may have increased risk of cancer development as this medicine suppresses the immune system.  The following medicines should be avoided while of Methotrexate: NSAIDS, Sulfonamides, Chloramphenicol, Phenytoin, Tetracycline, Bactrim, Trimethoprim, Dapsone, Retinoids, and Alcohol.