Characterization of etoricoxib, a novel, selective COX-2 inhibitor

Etoricoxib is a potent selective COX-2 inhibitor in man. Ex vivo whole-blood assays assessed COX-2 inhibition after oral administration of etoricoxib in single (5-500 mg) and multiple (25-150 mg) once-daily doses to healthy human subjects. A separate study examined ex vivo gastric mucosal PGE2 synthesis after etoricoxib (120 mg qd), naproxen (500 mg bid), or placebo for 5 days. The effect of etoricoxib 120 mg qd on the COX-1-mediated antiplatelet effects of low-dose aspirin (ASA) was also assessed. The mean (time)-weighted average inhibition (WAI) of lipopolysaccharide (LPS)-stimulated PGE2 (COX-2 assay) vcrsus placebo was dose related after single (range: 3.1%-99.1%) and multiple doses (range: 52.5%-96.7%). PGE2 remained significantly inhibited 24 hours postdose at steady state. Inhibition of LPS-stimulated PGE2 showed a strong relationship with etoricoxib plasma concentrations; ex vivo, IC50 was almost identical to in vitro. Multiple dosing of etoricoxib (up to 150 mg qd) showed no important effects on serum TXB2, bleeding time, or platelet aggregation (COX-1-mediated effects). The nonselective nonsteroidal anti-inflammatory (NSAID) naproxen significantly inhibited (approximately 78%) ex vivo prostaglandin synthesis in gastric mucosa; etoricoxib had no effect. Etoricoxib did not interfere with the antiplatelet effects of low-dose ASA, as assessed by serum TXB2 and platelet aggregation. Etoricoxib was generally well tolerated, even at doses above the clinical dose range. Based on these results, etoricoxib is a potent selective inhibitor of COX-2 after single and multiple dosing regimens and does not inhibit prostaglandin synthesis in the gastric mucosa, even at doses above the clinical dose range of 60 to 120 mg.