Opportunistic infection during treatment with low dose methotrexate.

Two patients receiving low dose methotrexate, one with rheumatoid arthritis and the other with pityriasis rubra pilaris, developed disseminated histoplasmosis and Mycobacterium avium intracellulare pneumonia, respectively. Twenty-three cases of opportunistic infection in patients receiving low dose methotrexate have been reported previously, with Pneumocystis carinii pneumonia being the most common infection (10 of 23, 43%). Patients receiving low dose methotrexate are at risk for opportunistic infection despite normal leukocyte counts.