Omeprazole
Omeprazole is the prototypical proton pump inhibitor, used in adults and children for gastro-oesophageal reflux disease, peptic ulcer disease, NSAID-induced ulcer prophylaxis and Helicobacter pylori eradication regimens.
- Chemical formula
- C17H19N3O3S
- CAS number
- 73590-58-6
- ATC code
- A02BC01
- Molecular weight
- 345.42 g/mol
- Drug class
- Proton pump inhibitor
- Also known as
- H 168/68, Omeprazol
What is it?
Omeprazole was the first proton pump inhibitor approved for clinical use, in 1989. It is supplied as oral capsules, tablets, oral suspension and parenteral solution. Omeprazole is dispensed both with and without prescription depending on dose and country, and is part of the World Health Organization List of Essential Medicines. It established a new class of acid-suppressive therapy that revolutionised the treatment of acid-related disorders.
Mechanism of action
Omeprazole is a substituted benzimidazole prodrug activated in the acidic environment of the gastric parietal cell, where it irreversibly inhibits the H+/K+-ATPase enzyme — the proton pump responsible for the final step in gastric acid secretion. Acid secretion gradually returns after discontinuation as new pumps are synthesised. Omeprazole is a racemic mixture of R and S enantiomers, with the S-enantiomer (esomeprazole) marketed separately.
Pharmacokinetics
Omeprazole is absorbed orally as enteric-coated formulations to protect against gastric acid degradation, with peak plasma concentrations reached after one to three hours. Bioavailability is approximately 30% to 40% after a single dose and increases with repeated dosing. Plasma protein binding is approximately 95%. The drug is metabolised by CYP2C19 (predominantly) and CYP3A4 to inactive metabolites. The terminal half-life is approximately one hour, although the antisecretory effect lasts much longer.
Indications
Omeprazole is approved in adults and children for the treatment of gastro-oesophageal reflux disease, including erosive oesophagitis healing, peptic ulcer disease, prevention of NSAID-induced ulcers, Zollinger-Ellison syndrome and as part of triple-therapy regimens for Helicobacter pylori eradication. According to clinical guidelines, the lowest effective dose for the shortest necessary duration should be used, with periodic reassessment of long-term therapy.
Safety profile
Common adverse effects include headache, gastrointestinal symptoms and dizziness. Long-term use has been associated with potential reductions in vitamin B12 and magnesium absorption, an increased risk of bone fractures, kidney injury and possible enteric infections including Clostridioides difficile. Omeprazole is a strong inhibitor of CYP2C19 and reduces the activation of clopidogrel; this interaction is clinically relevant. According to the prescribing information, long-term therapy should be regularly reassessed.
Products containing this ingredient
Frequently asked questions
How is omeprazole different from esomeprazole? ▾
Omeprazole is a racemic mixture of R and S enantiomers, while esomeprazole is the pure S-enantiomer. The S form has more consistent metabolism with higher bioavailability after multiple doses, particularly in CYP2C19 extensive metabolisers. Clinical efficacy is broadly comparable at equivalent doses, although esomeprazole may produce slightly faster healing in erosive oesophagitis. Choice between the two is made by the prescriber.
When should omeprazole be taken? ▾
Omeprazole is most effective when taken approximately 30 to 60 minutes before a meal, ideally before breakfast, because the proton pumps are most active during meals. According to the prescribing information, capsules should be swallowed whole with water, although they can be opened and the granules sprinkled on soft food in patients with swallowing difficulties. The granules must not be crushed or chewed.
Why does omeprazole reduce the effect of clopidogrel? ▾
Omeprazole is a strong inhibitor of CYP2C19, the enzyme that activates the antiplatelet prodrug clopidogrel to its active metabolite. Pharmacokinetic studies show reduced active metabolite concentrations and antiplatelet effect when these two drugs are co-administered. According to the prescribing information and several regulatory communications, the combination should be avoided when possible; alternative proton pump inhibitors such as pantoprazole are preferred in patients on clopidogrel.
Can omeprazole be taken long-term? ▾
Omeprazole is commonly used for prolonged periods in chronic GORD, Barrett's oesophagus and peptic ulcer prophylaxis with NSAIDs. Long-term use has been associated with potential reductions in vitamin B12 and magnesium absorption, an increased risk of bone fractures and possible enteric infections. According to international guidelines, long-term proton pump inhibitor therapy should be regularly reassessed, with the lowest effective dose used.
What are the main contraindications for omeprazole? ▾
Omeprazole is contraindicated in known hypersensitivity to omeprazole or substituted benzimidazoles, and in concurrent use with rilpivirine. Caution is required in severe hepatic impairment, in concurrent clopidogrel therapy, in long-term use with monitoring of magnesium and bone density and during pregnancy and breastfeeding. According to the prescribing information, the medical history must be reviewed by a clinician before any prescription.
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