Nimesulide is a selective cyclooxygenase-2 (COX-2) inhibitor. The IC₅₀ values are 70 and 1.27 µM for human recombinant COX-1 and -2 (at 20 µM arachidonic acid), respectively, and 22 and 0.03 µM for ovine COX-1 and -2 (at 100 µM arachidonic acid), respectively.