Omeprazole


Generic Medicine Info
Indications and Dosage
Intravenous
Zollinger-Ellison syndrome
Adult: In patients who are not suitable to receive oral formulation: Initially, 60 mg daily via IV infusion over 20-30 minutes or slow IV inj over 2.5 minutes, adjust dose according to response. Daily doses >60 mg should be given in 2 divided doses.

Intravenous
Duodenal ulcer, Gastric ulcer, Gastro-oesophageal reflux disease, NSAID-associated ulceration
Adult: In patients who are not suitable to receive oral formulation: 40 mg once daily via IV infusion over 20-30 minutes or slow IV inj over 2.5 minutes.

Oral
Acid-related dyspepsia
Adult: In relief of symptoms in patients with epigastric pain or discomfort with or without heartburn: 10 mg or 20 mg daily for 2-4 weeks. Treatment recommendations may vary among individual products and between countries (refer to specific product guidelines).

Oral
Eradication of Helicobacter pylori associated with peptic ulcer disease
Adult: As triple therapy: 20 mg bid for 7 or 10 days in combination with clarithromycin and with either amoxicillin or metronidazole (or tinidazole). Alternatively, 40 mg once daily for 1 week in combination with amoxicillin and metronidazole (or tinidazole). As dual therapy: 40 mg once daily for 14 days in combination with clarithromycin. Combination therapy consideration should be given to official local guidance regarding bacterial resistance, duration of treatment and appropriate use of antibacterial agents.
Child: As a component of triple therapy regimen with amoxicillin and clarithromycin: >4 years 15-30 kg: 10 mg bid for 1 week; >30 kg: 20 mg bid for 1 week. Combination therapy consideration should be given to official local guidance regarding bacterial resistance, duration of treatment and appropriate use of antibacterial agents.

Oral
Gastric ulcer
Adult: 20 mg once daily for 4-8 weeks, may increase to 40 mg once daily if needed. Maintenance therapy (prevention of ulcer relapse): 20 mg once daily, may increase to 40 mg once daily if needed. Dosing recommendations may vary among individual products and between countries (refer to specific product guidelines).

Oral
Duodenal ulcer
Adult: 20 mg once daily for 2-4 weeks, may increase to 40 mg once daily if needed. Maintenance therapy (prevention of ulcer relapse): 10-20 mg once daily, may increase to 40 mg once daily if needed. Dosing recommendations may vary among individual products and between countries (refer to specific product guidelines).

Oral
NSAID-associated ulceration
Adult: 20 mg once daily for 4 weeks, may continue for another 4 weeks if needed.

Oral
Gastro-oesophageal reflux disease
Adult: Symptomatic treatment of GERD: 10-20 mg once daily, adjust according to response. Dosing recommendations may vary among individual products and between countries (refer to specific product guidelines).
Child: Symptomatic treatment of heartburn and acid regurgitation: ≥1 year 10-20 kg: 10 mg once daily for 2-4 weeks, may increase to 20 mg once daily if needed; ≥2 years >20 kg: 20 mg once daily for 2-4 weeks, may increase to 40 mg once daily if needed. Dosing recommendations may vary among individual products and between countries (refer to specific product guidelines).

Oral
Reflux oesophagitis
Adult: Treatment: 20 mg once daily for 4-8 weeks. Severe cases: 40 mg once daily for 8 weeks. Maintenance therapy (after healing of oesophagitis): 10 mg once daily, may be increased to 20-40 mg once daily if needed. Dosing recommendations may vary among individual products and between countries (refer to specific product guidelines).
Child: Treatment: ≥1 year 10-20 kg: 10 mg once daily for 4-8 weeks, may increase to 20 mg once daily if needed; ≥2 years >20 kg: 20 mg once daily for 4-8 weeks, may increase to 40 mg once daily if needed. Dosing recommendations may vary among individual products and between countries (refer to specific product guidelines).

Oral
Zollinger-Ellison syndrome
Adult: Initially, 60 mg daily, adjust according to response. Usual dose: 20-120 mg daily. Daily doses of >80 mg should be given in 2 divided doses.

Oral
Prophylaxis of NSAID-induced ulcers
Adult: In at-risk patients (e.g. history of gastric or duodenal ulcer, or upper gastrointestinal bleeding) who require prolonged NSAID treatment: 20 mg once daily.
Special Patient Group
Pharmacogenomics:

Omeprazole is extensively metabolised in the liver mainly by CYP2C19 isoenzyme into hydroxyomeprazole (major metabolite).

CYP2C19 genotypes have been linked to PPI exposure, in which a lower exposure is associated with treatment failure while higher exposure is associated with improved efficacy. Higher exposure and long-term use of PPIs have also been associated with adverse effects.

The allele frequency of CYP2C19*2 (c.681G > A; rs4244285), the most common CYP2C19 non-functional allele, is approx 60% in Oceanians, approx 25-30% in Asians, and approx 15% in Europeans and Africans. The increased functional allele CYP2C19*17 (c.-806C > T; rs12248560) is most common in African, European, and Near Eastern populations, with approx 20% allele frequency.

Royal Dutch Pharmacists Association - Pharmacogenetics Working Group (DPWG) Guideline for omeprazole and CYP2C19 as of November 2018:
Phenotype Description Recommendation
CYP2C19 ultrarapid metaboliser Patients may have reduced omeprazole plasma concentrations resulting in lower effectiveness of omeprazole. For Helicobacter pylori (H. pylori) eradication therapy: Use a 3-fold higher dose and to advise patients to inform the doctor if dyspepsia symptoms persist. For other indications: Be alert for reduced effectiveness and use a 3-fold higher dose if necessary. Advise patients to report persisting symptoms of dyspepsia.

The DPWG guideline recommends to consider CYP2C19 genotyping on an individual basis before initiating omeprazole.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2C19 and PPIs as of August 2020:
Dosing recommendations for omeprazole based on CYP2C19 phenotype:
Phenotype and Genotype Implications Therapeutic Recommendations
CYP2C19 ultrarapid metaboliser

Individuals carrying 2 increased functional alleles e.g. *17/*17
Decreased omeprazole plasma concentrations as compared with CYP2C19 normal metabolisers and are at increased risk of therapeutic failure. Increase starting daily dose by 100%. Daily dose may be given in divided doses. Monitor for efficacy.
CYP2C19 rapid metaboliser

Individuals carrying 1 normal functional allele and 1 increased functional allele e.g. *1/*17
Decreased omeprazole plasma concentrations as compared with CYP2C19 normal metabolisers and are at increased risk of therapeutic failure.
Initiate standard starting daily dose. Consider increasing the dose by 50-100% for the treatment of H. pylori infection and erosive oesophagitis. Daily dose may be given in divided doses. Monitor for efficacy.
CYP2C19 normal metaboliser

Individuals carrying 2 normal functional alleles e.g. *1/*1
Normal omeprazole metabolism but may be at increased risk of therapeutic failure as compared with CYP2C19 intermediate and poor metabolisers. Initiate standard starting daily dose. Consider increasing the dose by 50-100% for the therapy of H. pylori infection and erosive oesophagitis. Daily dose may be given in divided doses. Monitor for efficacy.
CYP2C19 intermediate metaboliser

Individuals carrying 1 normal functional allele and 1 non-functional allele, or 1 increased functional allele and 1 non-functional allele e.g. *1/*2, *1/*3, *2/*17, *3/*17
Increased omeprazole plasma concentration as compared with CYP2C19 normal metabolisers and are at increased chance of efficacy and potential toxicity. Initiate standard starting daily dose. For chronic therapy (>12 weeks) and once efficacy is achieved, consider a 50% reduction in daily dose. Monitor for continued efficacy.
CYP2C19 poor metaboliser

Individuals carrying 2 non-functional alleles e.g. *2/*2, *3/*3, *2/*3
Increased omeprazole plasma concentration as compared with CYP2C19 normal metabolisers and are at increased chance of efficacy and potentially toxicity. Initiate standard starting daily dose. For chronic therapy (>12 weeks) and once efficacy is achieved, consider a 50% reduction in daily dose. Monitor for continued efficacy.
Hepatic Impairment
10-20 mg daily.
Administration
cap: Should be taken with food. Take immediately before a meal.
MUPS tab: May be taken with or without food.
powd for oral susp: Should be taken on an empty stomach. Take at least 1 hr before a meal.
delayed-release cap: Should be taken on an empty stomach. Take at least 1 hr before meals. Swallow whole, do not chew/crush. For patients w/ difficulty swallowing, cap may be carefully opened & entire contents sprinkled in a spoonful of applesauce. Swallow drug/food mixt w/o chewing immediately after prep. Drug/food mixt should not be stored for future use.
Reconstitution
Granules for oral susp: Empty the contents of the packet in the appropriate amount of water as indicated on the label. Leave the mixture to thicken then stir before drinking. Powder for oral susp: Reconstitute with the appropriate volume of water as indicated on the label. Shake well and leave the mixture to reach final consistency. Powder for solution for IV infusion: Dilute with 100 mL of dextrose 5% in water or NaCl 0.9% solution. Powder for solution for slow IV inj: Dilute with the 10 mL of solvent provided. Instructions for reconstitution may vary among individual products and between countries (refer to specific product guidelines).
Contraindications
Concomitant use with nelfinavir or rilpivirine.
Special Precautions
Patient with reduced body stores or risk factors for reduced vitamin B12 absorption; at risk of osteoporosis. May mask symptoms of gastric malignancy. CYP2C19 ultrarapid, rapid, normal, intermediate, and poor metabolisers. Hepatic impairment. Neonates, children, and elderly. Pregnancy and lactation.
Adverse Reactions
Significant: Hypomagnesaemia, vitamin B12 deficiency, fundic gland polyps (long-term use); cutaneous lupus erythematosus, subacute cutaneous lupus erythematosus (SCLE), SLE; osteoporosis-related fractures of the hip, wrist or spine (long-term use or high doses); Clostridium difficile-associated diarrhoea (CDAD), gastrointestinal infections (e.g. Salmonella, Campylobacter). Rarely, acute interstitial nephritis, hypersensitivity reactions (e.g. urticaria, angioedema, anaphylaxis, maculopapular rash).
Ear and labyrinth disorders: Vertigo.
Gastrointestinal disorders: Nausea, vomiting, diarrhoea, constipation, flatulence, abdominal pain.
General disorders and administration site conditions: Asthenia, malaise.
Investigations: Increased liver enzymes.
Metabolism and nutrition disorders: Peripheral oedema.
Musculoskeletal and connective tissue disorders: Back pain.
Nervous system disorders: Headache, dizziness, somnolence, paraesthesia.
Psychiatric disorders: Insomnia.
Respiratory, thoracic and mediastinal disorders: Cough, URTI.
Potentially Fatal: Very rarely, severe cutaneous adverse reactions (e.g. acute generalised exanthematous pustulosis, drug reaction with eosinophilia and systemic symptoms, Stevens-Johnson syndrome, toxic epidermal necrolysis).
Patient Counseling Information
This drug may cause dizziness and visual disturbances, if affected, do not drive or operate machinery.
Monitoring Parameters
Rule out presence of gastric malignancy prior to initiation of treatment. Monitor serum Mg levels before starting therapy and periodically thereafter; signs and symptoms of cutaneous lupus erythematosus or SLE, CDAD; bone loss and fractures (for those receiving high dose or in long-term therapy).
Overdosage
Symptoms: Nausea, vomiting, dizziness, drowsiness, blurred vision, tachycardia, abdominal pain, diarrhoea, dry mouth, diaphoresis, flushing, headache, apathy, depression, and confusion. Management: Symptomatic and supportive treatment.
Drug Interactions
May decrease the plasma concentrations of nelfinavir, rilpivirine, and atazanavir. Increased risk of hypomagnesaemia with diuretics. May increase the plasma concentrations of saquinavir, tacrolimus, methotrexate, citalopram. May significantly decrease the absorption of itraconazole, ketoconazole, posaconazole and erlotinib. May decrease metabolism of diazepam, phenytoin and cilostazol. May reduce the antiplatelet effect of clopidogrel; avoid concomitant use. May increase the bioavailability of digoxin. Increased INR and prothrombin time with warfarin. Concomitant use with CYP2C19 or CYP3A4 inhibitors (e.g. clarithromycin, voriconazole) may increase the plasma concentrations of omeprazole. Concomitant use with CYP2C19 or CYP3A4 inducers (e.g. rifampicin) may decrease the plasma concentrations of omeprazole.
Food Interaction
Decreased plasma concentration with St. John's wort.
Lab Interference
May increase the serum chromogranin A (CgA) levels which may cause false-positive result in the diagnostic test for neuroendocrine tumours.
Action
Description:
Mechanism of Action: Omeprazole is a substituted benzimidazole gastric antisecretory agent and is also known as proton pump inhibitor (PPI). It blocks the final step in gastric acid production by specific inhibition of H+/K+ adenosine triphosphatase (ATPase) enzyme system present on the secretory surface of the gastric parietal cell, thereby suppressing gastric acid secretion.
Onset: Antisecretory: Approx 1 hour.
Duration: Up to 72 hours.
Pharmacokinetics:
Absorption: Rapid but variably absorbed from the gastrointestinal tract. Bioavailability: Approx 30-40%. Time to peak plasma concentration: 0.5-3.5 hours.
Distribution: Enters breast milk. Plasma protein binding: Approx 95%.
Metabolism: Metabolised in the liver primarily by CYP2C19 isoenzyme into hydroxyomeprazole, and to a lesser extent by CYP3A4 into omeprazole sulfone.
Excretion: Mainly via urine (approx 77% as metabolites, small amount as unchanged drug); faeces. Elimination half-life: 0.5-1 hour.
Chemical Structure

Chemical Structure Image
Omeprazole

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 4594, Omeprazole. https://pubchem.ncbi.nlm.nih.gov/compound/Omeprazole. Accessed Feb. 27, 2023.

Storage
Store below 25°C. Protect from light and moisture. Storage recommendations may vary among individual products and between countries (refer to specific product guidelines).
MIMS Class
Antacids, Antireflux Agents & Antiulcerants
ATC Classification
A02BC01 - omeprazole ; Belongs to the class of proton pump inhibitors. Used in the treatment of peptic ulcer and gastro-oesophageal reflux disease (GERD).
References
Lima JJ, Thomas CD, Barbino J et al. Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2C19 and Proton Pump Inhibitor Dosing. Clinical Pharmacology & Therapeutics. 2020;0(0):1-7. doi:10.1002/cpt.2015. Accessed 02/03/2022

24 HR Omeprazole Tablet, Delayed Release (Meijer, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 21/11/2022.

Annotation of CPIC Guideline for Omeprazole and CYP2C19. Pharmacogenomics Knowledgebase (PharmGKB). https://www.pharmgkb.org. Accessed 02/03/2022.

Annotation of DPWG Guideline for Omeprazole and CYP2C19. Pharmacogenomics Knowledgebase (PharmGKB). https://www.pharmgkb.org. Accessed 02/03/2022.

Annotation of FDA Label for Omeprazole and CYP2C19. Pharmacogenomics Knowledgebase (PharmGKB). https://www.pharmgkb.org. Accessed 02/03/2022.

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Disclaimer: This information is independently developed by MIMS based on Omeprazole from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2024 MIMS. All rights reserved. Powered by MIMS.com
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