Serum histidine in rheumatoid arthritis: changes induced by antirheumatic drug therapy

Serum free histidine levels were studied in 15 patients with rheumatoid arthritis treated with D-penicillamine and 15 patients treated with hydroxychloroquine for 6 months. Both drugs produced improvement in the majority of patients, measured in terms of changes in 5 clinical parameters and plasma viscosity. A significant increase in serum histidine was observed only with D-penicillamine. This action, not seen with other specific antirheumatoid drugs may reflect a specific action of the drug.