Omeprazole is a cell-permeable, selective proton pump inhibitor. Omeprazole undergoes an acid-catalyzed rearrangement to a thiol-reactive cationic sulfenamide that inhibits (H+-K+)-ATPase in the gastric milieu. Omeprazole also acts as an aryl hydrocarbon-like inducer of cytochrome P450 secretion in human liver. This compound is an inhibitor a variety of CYP isoenzymes, including CYP2C19, CYP2C9 and CYP3A.