Esomeprazole is a proton pump inhibitor developed by Astra Zeneca in 2001 and marked under the trade name Nexium. Esomeprazole is the S-enantiomer of omeprazole (the racemate) and is an example of the controversial so-called “chiral switch” in with single isomers are developed and marked as having improved pharmacodynamic or phmacokinetic properties over the originally