Article: Omeprazole

Omeprazole
Systematic (IUPAC) name
5-methoxy-2-[(4-methoxy-3,5-dimethyl- pyridin-2-yl)methylsulfinyl]-3H-benzimidazole
Identifiers
CAS number	73590-58-6
ATC code	A02BC01
PubChem	4594
DrugBank	APRD00446
Chemical data
Formula	C17H19N3O3S
Mol. weight	345.4
Pharmacokinetic data
Bioavailability	35–60%
Metabolism	Hepatic (CYP2C19, CYP3A4)
Half life	1 - 1.2 hours
Excretion	80% Renal 20% Faecal
Therapeutic considerations
Pregnancy cat.	B3 (Australia)
Legal status	S4(AU) POM(UK)
Routes	Oral, IV

Omeprazole (INN) (IPA: [oʊˈmɛprəzoʊl]) is a proton pump inhibitor used in the treatment of dyspepsia, peptic ulcer disease (PUD), gastroesophageal reflux disease (GORD/GERD) and Zollinger-Ellison syndrome. It was first marketed by AstraZeneca as the magnesium salt omeprazole magnesium under the trade names Losec and Prilosec, and is now also available from generic manufacturers under various trade names. Omeprazole is one of the most widely prescribed drugs internationally and is available over the counter in some countries.

Faced with the loss of patent protection and competition from generic manufacturers, AstraZeneca developed, launched, and heavily marketed esomeprazole (Nexium), a single enantiomer form of omeprazole.

In 1990, in the U.S., at the FDA's request, the brand name Losec was changed to Prilosec to avoid confusion with the diuretic Lasix (furosemide).^[1] Unfortunately, the new name has lead to confusion between omeprazole (Prilosec) and fluoxetine (Prozac), an antidepressant.^[1]

Clinical use

Main article: Proton pump inhibitor

Use in Helicobacter pylori eradication

Omeprazole 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.

Dosage forms

Omeprazole is available as tablets and capsules (containing omeprazole or omeprazole magnesium) in strengths of 10 mg, 20 mg, and in some markets 40 mg; and as a powder (omeprazole sodium) for intravenous injection. Most oral omeprazole preparations are enteric-coated, due to the rapid degradation of the drug in the acidic conditions of the stomach. This is most commonly achieved by formulating enteric-coated granules within capsules, enteric-coated tablets, and the multiple-unit pellet system.

Multiple unit pellet system

Omeprazole tablets manufactured by AstraZeneca (notably Losec/Prilosec) are formulated as a "multiple unit pellet system" (MUPS). Essentially, the tablet consists of extremely small enteric-coated granules (pellets) of the omeprazole formulation inside an outer shell. When the tablet is immersed in an aqueous solution, as happens when the tablet reaches the stomach, water enters the tablet by osmosis. The contents swell from water absorption causing the shell to burst, releasing the enteric-coated granules. For most patients, the multiple-unit pellet system is of no advantage over conventional enteric-coated preparations. Patients for which the formulation is of benefit include those requiring nasogastric tube feeding and those with difficulty swallowing (dysphagia).

The granules are manufactured in a fluid air bed system. sugar spheres in suspension are sequentially sprayed with aqueous suspensions of omeprazole, a protective layer, an enteric coating and an outer layer to reduce granule aggregation. The granules are mixed with other excipients and compressed into tablets. Finally, the tablets are film-coated to improve the stability and appearance of the preparation.

Immediate release formulation

In June 2004 the FDA approved an immediate release preparation of omeprazole/sodium bicarbonate that does not require an enteric coating. This preparation employs sodium bicarbonate as a buffer to protect omeprazole from gastric acid degradation. This allows for the production of chewable tablets. This combination preparation is marketed in the United States by Santarus under the trade name Zegerid. Zegerid is marketed as capsules, chewable tablets, and powder for oral suspension. Zegerid is most useful for those patients who suffer from nocturnal acid breakthrough (NAB) or those patients who desire immediate relief.