Inability to interpret toxic salicylate levels in patients taking aspirin and diflunisal.
Diflunisal, a nonsteroidal antiinflammatory drug, is not metabolized to the free salicylate moiety, but yields serum salicylate levels. We describe 2 patients who unexpectedly had toxic range serum salicylate levels while taking diflunisal and aspirin for rheumatoid arthritis. Diflunisal is measured by standard salicylate assays, a fact not widely appreciated. Serum salicylate levels by these assays cannot be used to determine salicylate toxicity when a patient is taking both aspirin and diflunisal. High pressure liquid chromatography can be used to distinguish true salicylate toxicity from interference with diflunisal.
Adelman
H M
HM
Department of Internal Medicine, University of South Florida College of Medicine, Tampa 33612.
Wallach
P M
PM
Flannery
M T
MT
D001172:Arthritis, Rheumatoid / Q000097:blood / Q000188:drug therapy*; D001241:Aspirin / Q000627:therapeutic use*; D004061:Diflunisal / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012459:Salicylates / Q000097:blood / Q000506:poisoning*
D012459:Salicylates; D004061:Diflunisal; D001241:Aspirin