Sulphasalazine for rheumatoid arthritis: relationship between dose, acetylator phenotype and response to treatment.

Sulphasalazine is an effective treatment for rheumatoid arthritis but the response in any individual is unpredictable. We have sought to establish a relationship between dose (in mg/kg body weight) and metabolism of the drug in 79 patients selected for an extremely good response (43) or no response (36) to treatment with sulphasalazine. The dose of sulphasalazine in relationship to body weight showed no difference between the two treatment outcome groups. The distribution of acetylator phenotype showed only a trend for slow acetylators to occur more frequently in the group of good responders to treatment. There is no advantage in the routine assessment of acetylator phenotype as a predictor of response to treatment with sulphasalazine.