What is Omeprazole? Everything You Need to Know

What is Omeprazole? Learn more about this representative drug of the group of drugs called proton-pump inhibitors that are used for gastric problems.
What is Omeprazole? Everything You Need to Know
María Vijande

Reviewed and approved by the pharmacist María Vijande.

Written by María Vijande

Last update: 09 October, 2022

Omeprazole is the representative drug of the group of drugs called proton-pump inhibitors. These are used for stomach problems like acidity and gastritis, among others.

We are going to explain the following aspects referring to omeprazole:

  • Mechanism of action
  • Pharmacokinetics
  • Metabolism
  • Adverse side effects
  • Interactions
  • Indications

How it Works

The stomach possesses an acidic pH. This is because of the HCI that is produced by the parietal cells that are found in the gastric mucous.

Actually, your stomach’s acidic pH is essential for digestion of foods in order to:

  • Correctly break down proteins.
  • Activate the pepsin to peptide so that it can produce proteolysis, or the rupture of the peptide bonds of the proteins.
  • Prevent bacterial infections since the bacteria don’t usually survive the acidity.

In addition, an excess secretion of gastric acid can cause damage to the gastrointestinal tract’s mucous. This mainly produces stomach ulcers and duodenum.

Stomach cell

Stages of Acid Secretion

The secretion of gastric acid takes place in various steps:

  1. Segregation of the ions H+ and Cl- separately in the parietal cells
  2. Their combination to form HCl in the canaliculi
  3. Segregation of acid also from the canaliculus to line the stomach

The proton-pump inhibitors, like omeprazole, acts in the final step of the acid production, irreversibly combing the ATPH+/K-, a pH dependent binding with a maximum pH<6.

This inhibition takes place through the formation of the covalent bond S-S between sulfamide and a cysteine residue that is accessible to the proton-pumps. This, this links the residue Cys-813 and Ces-892.

Omeprazole, similar to other proton-pump inhibitors, is administered in its neutral form, which is inactive. Moreover, being in its neutral form, it is lipophilic. This means it is insoluble in water and is capable of crossing the cellular membrane easily without any problems.

Since these cells have an acidic pH, they transform the omeprazole from its neutral form to its active protonated form. This makes it capable of finishing the mechanism of action and irreversibly binding it to the proton-pump and blocking its action.

  • It is labile in acid so that the oral preparations are equipped with an enteric cover
  • The bond of the plasmatic proteins increases. More than 95%, which increases its ability of interaction with other drugs, since it may experience a shift in the dosage
  • Moreover, it is usually completely absorbed by the small intestine between 3-6 hours
  • The oral bioavailability is approximately 35%, and can increase up to 60% when repeated administration once a day
  • Its distribution volume ranges 0.3 L/Kg


Omeprazole suffers hepatic metabolism through the CYP 45o system. So the majority of our metabolism depends on the specific isoenzyme CYP2C19.

Further, the majority of the doses administered orally excrete inactive metabolites through urine and the remainder through feces mainly from biliary secretion.

Adverse side effects

You have to keep in mind that omeprozale can present a number of adverse side effects, although not many due to the selectivity in its action, it must be kept in mind if this drug is administered. Among them are:

  • Prolonged treatments can produce serious hypomagnesemia 
  • Increases the risk of fractured bones
  • Changes in skin like itching and rashes
  • Gastrointestinal changes like diarrhea, constipation, abdominal pain, nausea, or vomiting
Woman with nausea
  • Peripheral neuropathy
  • Hypersensibility
  • Hemolytic anemia
  • Reduction in the absorption of vitamin B12, so it can increase the risk of suffering from megaloblastic anemia
  • Risk of subacute cutaneous lupus erythematosus (lupus)
  • Increase in the levels of chromogranin A, the protein also found to be high in certain types of cancer


Omeprazole interacts with enough drugs that, when administered simultaneously, reduce or increase its action.

It can reduce the action of:

  • Clopidrogerel
  • Antifungals
  • Phenytoin
  • Mycophenolate
  • Others

It can increase the action of:

  • Methotrexate
  • Amphetamines
  • Benzodiazepines
  • Carvedilol
  • Citalopram
  • Escitalopram
  • Cyclosporine
  • Warfarin
  • Others

Ultimately, it can also interact with numerous drugs. So if you are taking omeprazole with some other medication, consult your doctor to prevent any complications.


Used for:

  • Gastric ulcers
  • Duodenal ulcers
  • Esophagitis caused by reflux
  • Zollinger- Ellison syndrome
  • Gastritis
  • Functional dyspepsia

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • Ministerio, S. y C. (2012). Ficha técnica Omeprazol.
  • Molero, R., Sacristán de Lama, M. P., López, C., Mangues, I., Socias, M. S., & Piñeiro, G. (1997). Utilización Terapéutica del Omeprazol. Sociedad Española de Farmacia Hospitalaria.
  • Callejas Díaz, A., Montero Hernández, E., Gil Navarro, M., Tutor-Ureta, P., Yebra Bango, M., & Vargas Núñez, J. A. (2011). Omeprazol e hipomagnesemia. Revista Clinica Espanola. https://doi.org/10.1016/j.rce.2011.01.013
  • Sánchez, L. J., Nombela, A. M., Velázquez, C. B., Hernández, S. H., & Carretón, M. a. J. A. (2016). Efectos adversos del consumo crónico de omeprazol. FMC Formacion Medica Continuada En Atencion Primaria. https://doi.org/10.1016/j.fmc.2016.01.007

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.