Ilaprazole (IY-81149) is a proton pump inhibitor; inhibits H⁺/K⁺-ATPase with an IC₅₀ of 6.0 μM. IC50 & Target: IC50: 6.0 μM (H⁺/K⁺-ATPase)^[1] In Vitro: In rabbit parietal cells, ilaprazole irreversibly inhibits H⁺/K⁺-ATPase in dose-dependent manner with an IC₅₀ of pump inhibitory activity of 6.0 μM. The IC₅₀ of ilaprazole is 9.0 nM on cumulation of ¹⁴C-aminopyrine in histamine stimulated parietal cells^[1]. In Vivo: In pylorus-ligated rats, ilaprazole shows strong inhibitory activity against gastric acid secretion. The ED₅₀ of ilaprazole administered intraduodenally is 1.6 mg/kg. For oral administration, the ED₅₀ of ilaprazole is 1.94 mg/kg. Ilaprazole also significantly inhibits pentagastrin-stimulated gastric secretion. Its ED₅₀ is 2.1 mg/kg. In Heidenhain pouch dogs, the acid output is completely blocked at 0.3 mg/kg, 135 min after i.v. administration^[1]. Intravenous ilaprazole exhibits high antiulcer activity in a dose-dependent manner. Ilaprazole at a dose of 3 mg/kg decreases ulcer number and index to the same extent as 20 mg/kg esomeprazole. Moreover, the potency of intravenous ilaprazole is superior to that of intragastric ilaprazole. In anesthetized rats, the inhibitory effect of intravenous ilaprazole on histamine-induced acid secretion is faster and longer-lasting than that of intraduodenal ilaprazole^[2].