Low dose methotrexate is usually a relatively safe therapy for rheumatoid arthritis, psoriasis and other immune-based conditions. However, some patients may develop bone marrow depression with significant pancytopenia.


Risk factors for bone marrow suppression with low dose methotrexate therapy:

(1) dose error made by the physician

(2) error made by the pharmacist in reading or filling the prescription

(3) error by the patient in taking too much of the drug (typically since the drug is often given only once a week)

(4) transient or progressive renal insufficiency

(5) drug interference

(6) marked decrease in oral folic acid intake


Drugs which may interfere with methotrexate elimination:


(2) antibiotics (penicillin, tetracycline, chloramphenicol, kanamycin, trimethroprim, co-trimoxazole)

(3) corticosteroids

(4) cyclosporine

(5) cisplatin

(6) nitrous oxide (most exposures should be infrequent unless the patient is an anesthetist or abusing the drug)

(7) opremazole

(8) probenecid

(9) retinoids

(10) triameterene


In some patients none of these risk factors can be found. The differential diagnosis may include myelodysplasia, viral infection or toxic exposure.


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