Decrease of in vitro serum protein binding of salicylate in rheumatoid arthritis.

Free and bound fractions of salicylates were separated by equilibrium dialysis and measured by spectrofluorimetry in 27 patients with rheumatoid arthritis and in 16 controls. The results showed that in patients with rheumatoid arthritis, the binding of salicylate to proteins decreased in an overproportional manner with the decrease of serum albumin concentrations. This phenomenon was linked with the severity of the inflammatory syndrome. The saturation binding capacity per unit of protein concentration was lower in the patients suffering from active forms of the condition, a finding which suggests that the changes observed are not due only to quantitative changes in the serum albumins. This study confirms the importance of determining free salicylate concentrations in the treatment of patients with inflammatory diseases.