In vivo effects of meloxicam and aspirin on blood, gastric mucosal, and synovial fluid prostanoid synthesis in dogs

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Abstract
Objective—To evaluate in vivo activityin dogs of meloxicam or aspirin, previously shown in vitro to be a selective cyclooxygenase-2 (COX-2) inhibitor (COX-1 sparing drug), or a nonselective COX inhibitor, respectively.Animals—12 male dogs with unilateral osteoarthritis of the stifle joint.Procedure—Each dog was treated in a crossover design with aspirin or meloxicam for 21 days. Prostaglandin E2(PGE2) concentrations were measured at days 0 (baseline), 7, and 21 of each treatment period in lipopolysaccharide (LPS)-stimulated blood, synovial fluid collected by arthrocentesis, and endoscopic gastric mucosal biopsy specimens. Thromboxane B2(TXB2) was evaluated in blood on days 0, 7, and 21 of each treatment period.Results—Aspirin administration significantly suppressed PGE2concentrations in blood, gastric mucosa, synovial fluid, and suppressed TXB2concentration in blood at days 7 and 21. Meloxicam administration significantly suppressed PGE2concentrations in blood and synovial fluid at days 7 and 21, but had no effect on concentrations of TXB2 in blood or PGE2in gastric mucosa. Suppression of LPS-stimulated PGE2concentrations in blood and synovial fluid by aspirin and meloxicam administration is consistent with activity against the COX-2 isoenzyme. Suppression of concentrations of PGE2in the gastric mucosa and TXB2in blood by aspirin administration is consistent with activity against COX-1. Meloxicam, in contrast, had a minimal effect on functions mediated by COX-1.Conclusions and Clinical Relevance—Meloxicam acts in vivo in dogs as a COX-1 sparing drug on target tissues by sparing gastric PGE2synthesis while retaining antiprostaglandin effects within inflamed joints. (Am J Vet Res2002;63:1527–1531)