Omeprazole is a proton pump inhibitor used in the treatment of dyspepsia, peptic ulcer disease (PUD), gastroesophageal reflux disease (GORD/GERD), laryngopharyngeal reflux (LPR), and Zollinger-Ellison syndrome. It was first marketed in the US in 1989 by AstraZeneca under the brand names Losec and Prilosec, and is now also available from generic manufacturers under various brand names. AstraZeneca markets omeprazole as Losec, Antra, Gastroloc, Mopral, Omepral, and Prilosec. Omeprazole is marketed as Zegerid by Santarus, Prilosec OTC by Procter & Gamble and Zegerid OTC by Schering-Plough. In India it is available as OMEZ (FGP). Omeprazole is one of the most widely prescribed drugs internationally and is available over the counter in some countries. Pharmacology
Omeprazole is a racemate. It contains a tricoordinated sulfur atom in a pyramidal structure and therefore can exist in equal amounts of both the S and R enantiomers. In the acidic conditions of the stomach, both are converted to achiral products, which react with a cysteine group in H+/K+ ATPase, thereby inhibiting the ability of the parietal cells to produce gastric acid. Name change
In 1990, at the request of the U.S. Food and Drug Administration (FDA), the brand name Losec was changed to Prilosec to avoid confusion with the diuretic Lasix (furosemide). Unfortunately, the new name has led to confusion between omeprazole (Prilosec) and fluoxetine (Prozac), an antidepressant. Clinical use
Use in Helicobacter pylori eradication
Omeprazole is combined with the antibiotics clarithromycin and amoxicillin (or metronidazole in penicillin-hypersensitive patients) in the 7-14 day eradication triple therapy for Helicobacter pylori. Infection by H. pylori is the causative factor in the majority of peptic and duodenal ulcers.
Some of the most frequent side effects of omeprazole (experienced by over 1% of those taking the drug) are headache, diarrhea, abdominal pain, nausea, dizziness, trouble awakening and sleep deprivation, although in clinical trials the incidence of these effects with omeprazole was mostly comparable to that found with placebo. Proton pump inhibitors may be associated with a greater risk of hip fractures, and clostridium difficile-associated diarrhea. ] Patients are frequently administered the drugs in intensive care as a protective measure against ulcers, but this use is also associated with a 30% increase in occurrence of pneumonia. Other side effects may include bone rebuild interference and B12 vitamin reduction.
Omeprazole is a competitive inhibitor of the enzymes CYP2C19 and CYP2C9, and may therefore interact with drugs that depend on them for metabolism, such as diazepam, escitalopram, and warfarin; the concentrations of these drugs may increase if they are used concomitantly with omeprazole.Clopidogrel (Plavix) is an inactive prodrug that partially depends on CYP2C19 for conversion to its active form; inhibition of CYP2C19 blocks the activation of clopidogrel, thus reducing its effects and potentially increasing the risk of stroke or heart attack in people taking clopidogrel to prevent these events.Omeprazole is also a competitive inhibitor of p-glycoprotein, as are other PPIs. Drugs that depend on stomach pH for absorption may interact with omeprazole; drugs that depend on an acidic environment (such as ketoconazole or atazanavir) will be poorly absorbed, whereas drugs that are broken down in acidic environments (such as erythromycin) will be absorbed to a greater extent than normal. St. John's wort (Hypericum perforatum) and Gingko biloba significantly reduce plasma concentrations of omeprazole through induction of CYP3A4 and CYP2C19.
Absorption and distribution
The absorption of omeprazole takes place in the small...
Bibliography: Omeprazole Monograph. Oxford Clinical Communications, 1988.
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