Phenylbutazone is a member of the class of pyrazolidines that is 1,2-diphenylpyrazolidine-3,5-dione carrying a butyl group at the 4-position. It has a role as a non-narcotic analgesic, a non-steroidal anti-inflammatory drug, an antirheumatic drug, a peripheral nervous system drug, a metabolite and an EC 1.1.1.184 [carbonyl reductase (NADPH)] inhibitor.