Proton pump inhibitors (PPIs) are the most potent acid suppressants available. PPIs undergo hepatic metabolism via the CYP2C system for the isoforms CYP2C19 and CYP3A4 in particular. Genetic polymorphisms in CYP2C19 may affect the metabolism of individual PPIs to different extents. Although PPIs are highly effective as a class, differences in their pharmacokinetics, such as bioavailability and metabolism, may translate into differences in clinical outcomes. In Helicobacter pylori infection, a significantly lower eradication rate was seen in extensive metabolizers with omeprazole but no with rabeprazole.