Esomeprazole
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(S)-5-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl) methyl]sulfinyl]-1H-benzimidazole | |
| Empirical formula | C34H36N6O6S2 |
| Molecular weight | 688.8 |
| Bioavailability (Oral) | 50-89% |
| Metabolism | hepatic CYP2C19, CYP3A4 |
| Elimination half life (Oral) | 1.3 hour |
| Excretion | 80% renal, 20% faecal |
| Pregnancy category | B3 (Australia) |
| Legal status | Schedule 4 (Australia) POM (UK) |
| Routes of administration | oral |
Esomeprazole is a proton pump inhibitor used in the treatment of dyspepsia, peptic ulcer disease (PUD), GERD and Zollinger-Ellison syndrome. Esomeprazole magnesium trihydrate is marketed by AstraZeneca under the tradename Nexium®. Esomeprazole is the S-enantiomer of omeprazole (marketed as Losec® & Prilosec®), and AstraZeneca claims improved efficacy of this single enantiomer product over the racemic mixture of omeprazole (see below). In other words, the only chemical difference between the two is that omeprazole has both "left handed" and "right handed" forms of the same molecule, while esomeprazole only has one form.
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Use in Helicobacter pylori eradication
Esomeprazole is combined with the antibiotics clarithromycin and amoxicillin (or metronidazole in penicillin-hypersensitive patients) in the one week eradication triple therapy for Helicobacter pylori. Infection by H. pylori is the causative factor in the majority of peptic and duodenal ulcers.
Clinical use
Main article: Proton pump inhibitor
Evidence of efficacy
AstraZeneca claims that esomeprazole provides improved efficacy, in terms of stomach acid control, over racemic omeprazole. Many health professionals have expressed the view that this improvement in efficacy is due to the increased dose of (es)omeprazole recommended for therapy rather than any superiority of esomeprazole per se.
The study usually cited by AstraZeneca to support its claims is of doubtful study power. Lind et al. (2004) compared esomeprazole to omeprazole in a study of only 36 GERD patients. It is noted that this study was financially supported by AstraZeneca itself.
An alternative rationale suggested for the use of esomeprazole was the reduction in interindividual variability in efficacy. There is, however, little evidence for even this advantage. (Somogyi et al., 2004)
Given the large difference in cost between esomeprazole and other proton pump inhibitors and the negligible advantages of esomeprazole, many doctors recommend cheaper alternatives, which in most cases work just as well.
Multiple-unit pellet system
Nexium tablets are formulated as a "multiple-unit pellet system". Essentially, the tablet consists of enteric-coated granules (pellets) of the esomeprazole formulation inside an outer shell. When the tablet is swallowed, the contents swell from water absorption, bursting the shell - releasing the tablet contents. The multiple-unit pellet system is often demonstrated to pharmacists and doctors by AstraZeneca sales representatives despite having little advantage, pharmacokinetically, over a regular enteric-coated tablet.
References
- Lind T., Rydberg L., Kyleback A., Jonsson A., Andersson T., Hasselgren T., Holmberg J., Rohss K. (2004). Esomeprazole provides improved acid control vs omeprazole in patients with symptoms of gastro-oesophageal reflux disease. Aliment Pharmacol Ther 14, 861-867.
- Somogyi A., Bochner F., Foster D. (2004). Inside the isomers: the tale of chiral switches. Aust Prescr 27, 47-49.
- Gladwell M., High Prices (http://www.newyorker.com/critics/atlarge/?041025crat_atlarge), New Yorker, Oct 2004. This article describes AstraZeneca's strategy for developing Nexium as a follow-on for Losec as the latter approached patent expiry.