Esomeprazole is the S-isomer of omeprazole and a proton pump inhibitor that irreversibly blocks the H+/K+-ATPase enzyme in gastric parietal cells. Its enantiomerically pure formulation offers more predictable plasma levels and sustained acid suppression compared with racemic omeprazole. Indicated for gastro-oesophageal reflux disease (GERD), erosive oesophagitis, prevention of NSAID-associated gastric ulcers, eradication of Helicobacter pylori in combination with antibiotics, and management of Zollinger-Ellison syndrome.