A phenylbutazone dose-finding study in rheumatoid arthritis

Different doses of phenylbutazone have been compared in a double blind study on 32 patients with rheumatoid arthritis in order to determine the minimum effective dose. Of 8 different dose levels studied (90 mg, 150 mg, 180 mg, 240 mg, 270 mg, 300 mg, 360 mg and 450 mg/day) the most efficacious was found to be 300 mg/day. Doses below this did not produce full benefit; no further improvement occurs with higher doses. Although 7/32 patients developed adverse reactions there was no relationship between these and the plasma levels of either phenylbutazone or oxyphenbutazone. An attempt was made to distinguish ‘responders’ from ‘non-responders’. We found no relationship between response and plasma levels of phenylbutazone or oxyphenbutazone.