Macrocytic anaemia in patients treated with sulfasalazine for rheumatoid arthritis.

Sulphasalazine is a "disease modifying" drug that is now widely used in rheumatoid arthritis, having fewer and milder side effects than gold or penicillamine.' One potential side effect, which is easily missed and may become life threatening, is macrocytic anaemia. This occurs in 2-3% of prising and possibly to "reflect the brittle state of folate metabolism in rheumatoid arthritis." Since then the development of macrocytic anaemia during treatment with sulphasalazine has been mentioned in reports but has drawn little attention. Recently it was suggested that sulphasalazine does not cause folate deficiency in rheumatoid arthritis at a dose below 2 g/day,5 but the number of patients and duration of the study do not allow a definite conclusion to be reached. Certainly, folic acid deficiency is more likely to occur when additional causes of it are present and when sulphasalazine is given in higher dosage. It is an important complication as it is potentially serious, easily treated, and not an indication for stopping sulphasalazine.