Azathioprine in rheumatoid arthritis: double-blind study of full versus half doses versus placebo

Abstract

To test whether azathioprine in effective in rheumatoid arthritis in doses smaller than those normally used the drug was tested at 2 dosage levels, 2.5 and 1.25 mg/kg/day (2.5 AZ and 1.25 AZ), against placebo under double-blind conditions over 24 weeks. Dropouts were 7 out of 15 in the 2.5 AZ group, 4 out of 14 in the 1.25 AZ group, and 2 out of 13 in the placebo group. Some significant improvement occurred in all 3 groups, including those on placebo. However, the 2.5 AZ group fared significantly better than the placebo group, while the 1.25 AZ group results tended to fall between the other 2 groups. We conclude that, in order to obtain the reported effectiveness of azathioprine in rheumatoid arthritis, it is necessary to start treatment with 2.5 mg/kg/day. Halving this dosage reduces the effectiveness of the drug.