NS-398 is a non-steroidal an-inflammatory agent with analgesic and antipyretic effects, and selectively inhibits prostaglandin G/H synthase 2/cyclooxygenase 2 (COX-2) activity, with an IC₅₀ of 3.8 μM, and has no effect on COX-1 at 100 μM. IC50 & Target: IC50: 3.8 μM (COX-2)^[1] In Vitro: NS-398 is a non-steroidal an-inflammatory agent, selectively inhibits prostaglandin G/H synthase/cyclooxygenase (COX-2) activity, with an IC₅₀ of 3.8 μM, and has no effect on COX-1 at 100 μM^[1]. NS-398 weakly inhibits PG endoperoxide synthase activity from sheep seminal vesicle microsomes (IC₅₀, 11 μM)^[2]. In Vivo: NS-398 (0.5-10 mg/kg, p.o.) dose-dependently inhibits paw edema in rats, with an ED₃₀ of 1.14 mg/kg, shows therapeutic effects on adjuvant arthritis (ED₃₀, 4.69 mg/kg), exhibits dose-dependent analgesic activity (ED₅₀, 1.65 mg/kg), and has antipyretic effect (ED₅₀, 1.84 mg/kg) in rats. In mice, NS-398 suppresses writhing reactions induced by acetic acid with an ED₅₀ of 8.2 mg/kg^[2].