'Antiulcer drugs are a class of drugs, exclusive of the antibacterial agents, used to treat ulcersin the stomach anastric and duodenal ulcers are caused by Helicobacter pylori infections, and aretreated with combination treatments that incorporate antibiotic therapy with gastric acidsuppression. Additionally, bismuth compounds have been used. The primary class of drugsused for gastric acid suppression are the proton pump inhibitors, omeprazole, lansoprazole,pantoprazole and rabeprazole. The H-2 receptor blocking agents, cimetidine, famotidine,nizatidine, and ranitidine have been used for this purpose, but are now more widely used formaintenance therapy after treatment with the proton pump inhibitors . The proton pump inhibitors block the secretion of gastric acid by the gastric parietal cells.The extent of inhibition of acid secretion is dose related. In some cases, gastric acid secretionis completely blocked for over 24 hours on a single dose. In addition to their role in treatment ofgastric ulcers, the proton pump inhibitors are used to treat syndromes of excessive acidsecretion (Zollinger-Ellison Syndrome) and gastroesophageal reflux disease (GERD).