Bone marrow suppression can occur even with low doses of methotrexate

Methotrexate is an antimetabolite that, apart from its use in malignant disorders, is taken orally in low doses for the control of conditions such as rheumatoid arthritis and psoriasis. When used in chemotherapy it causes profound suppression of bone marrow. However, even at a low dose it may be associated with bone marrow suppression—particularly in the presence of renal insufficiency or when other drugs are taken concomitantly (box 1). Its unusual weekly dosing regimen can result in dose error by patients or clinicians. We present three cases of bone marrow suppression in patients taking low dose methotrexate who presented at a district general hospital during a period of four years (table).