5-Aminosalicylic acid or sulphapyridine. Which is the active moiety of sulphasalazine in rheumatoid arthritis?

Thirty patients with active rheumatoid arthritis participated in an open study of 6 months' treatment with either 5-aminosalicylic acid or sulphapyridine, the two moieties of sulphasalazine. Patients were assessed at regular intervals using a number of clinical and biochemical tests designed to detect specific antirheumatic activity. Patients taking sulphasalazine showed significant improvement in most parameters of disease activity, but those taking 5-aminosalicylic acid did not improve despite the fact that high serum concentrations of 5-aminosalicylic acid and acetyl 5-aminosalicylic acid were achieved. These results suggest that sulphapyridine is the active moiety of sulphasalazine. Its possible mode of action is discussed. Nausea was a frequent problem in patients taking sulphapyridine. Unless this problem can be overcome, sulphapyridine is unlikely to offer any therapeutic advantages over sulphasalazine in the treatment of rheumatoid arthritis.