YH4808, as a selective K+- competitive acid blocker (P-CAB), is no need for activation by gastric acid since it competitively inhibits proton pump with K+. Thus, the inhibition of gastric acid secretion by YH4808 is prompt and effective. In addition, the inhibitive effect of gastric acid secretion by stimulation of histamine is proved to be more powerful than PPI (esomeprazole) and sustained in in-vitro/in-vivo model, and 24-h inhibition of gastric acid secretion and especially nocturnal inhibition of gastric acid secretion was observed to be superior to esomeprazole with repeat doses for 7 days in healthy volunteers.