Lowering of plasma isoxicam concentrations with acetylsalicylic acid.

The pharmacokinetics of isoxicam 200 mg administered orally in 10 healthy male volunteers was studied before and during administration of acetylsalicylic acid 3.9 g daily by mouth starting 5 days after isoxicam. There was a statistically significant decrease in plasma isoxicam concentrations, but no significant change in time to reach maximum plasma concentration or disappearance time. The mechanisms of this interaction is probably competitive displacement of isoxicam from albumin by acetylsalicylic acid or salicylate. These results are consistent with the known effect of ASA in producing competitive displacement of other protein bound antiinflammatory drugs.