Formulary
Omeprazole: Uses, Dosing, Side Effects and Indian Brand Names
Omeprazole is the prototype proton pump inhibitor that irreversibly inhibits H+/K+ ATPase in parietal cells. It is first-line for peptic ulcer disease, GERD, and part of H. pylori eradication regimens, with long-term use concerns including hypomagnesaemia and fracture risk.
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Omeprazole: Uses, Dosing, Side Effects and Indian Brand Names
Omeprazole is the prototype proton pump inhibitor that irreversibly inhibits H+/K+ ATPase in parietal cells. It is first-line for peptic ulcer disease, GERD, and part of H. pylori eradication regimens, with long-term use concerns including hypomagnesaemia and fracture risk.
NEET PG High-Yield: PPIs irreversibly inhibit H+/K+ ATPase (proton pump). Must be taken before meals (need active pumps). Omeprazole interacts with clopidogrel via CYP2C19 -- a very high-yield MCQ topic. Long-term risks: hypomagnesaemia, B12 deficiency, C. difficile, fractures. In Zollinger-Ellison syndrome, PPIs are the drugs of choice (high-dose).
Clinical overview
Omeprazole was the first proton pump inhibitor introduced (1989) and revolutionised the treatment of acid-related disorders. It is the most widely used PPI in India and remains a cornerstone drug for peptic ulcer disease, gastro-oesophageal reflux disease (GERD), and H. pylori eradication therapy. Because omeprazole irreversibly inhibits the proton pump, acid secretion resumes only when new pump molecules are synthesised (half-life of pump turnover is approximately 18 hours), so once-daily dosing provides 24-hour acid suppression despite the drug's short plasma half-life (0.5-1 hour). The drug should be taken 30 minutes before breakfast for maximal efficacy, as it requires active proton pumps to generate the acidic environment for its activation. Omeprazole is a CYP2C19 substrate and a moderate CYP2C19 inhibitor, leading to clinically significant interactions with clopidogrel (reduced activation of clopidogrel, diminished antiplatelet effect -- this has been an FDA safety concern). Long-term PPI use (>1 year) has been associated with hypomagnesaemia, vitamin B12 deficiency, Clostridium difficile infection, community-acquired pneumonia, and hip fractures (reduced calcium absorption), though the absolute risk increase is small. In India, omeprazole is one of the most commonly prescribed drugs overall, often used inappropriately for long durations without clear indication.
Pharmacological class
Omeprazole belongs to the Proton pump inhibitor (PPI; substituted benzimidazole) class. Omeprazole is a prodrug that accumulates in the acidic environment of parietal cell canaliculi, where it is converted to its active form (sulphenamide). This active form irreversibly binds to and inhibits the hydrogen-potassium ATPase (H+/K+ ATPase, the proton pump) on the luminal surface of parietal cells. As this is the final common pathway for acid secretion, omeprazole produces a more complete and sustained acid suppression than H2 receptor antagonists, reducing basal and stimulated acid secretion by 80-95%.
Indian brand names and formulations
Available as: Omez (Dr Reddy's Laboratories), Ocid (Zydus Cadila), Omecip (Cipla), Omesec (Alkem Laboratories).
Capsules (10 mg, 20 mg, 40 mg), Enteric-coated tablets (20 mg), IV injection (40 mg vial for reconstitution), Oral suspension (sachet formulation for paediatrics), Combination with domperidone (Omez-D)
Regulatory status
Omeprazole is classified under Schedule H in India under the Drugs and Cosmetics Act, 1940. Schedule H prescription drug, though widely available at pharmacies in practice. NLEM 2022 listed. One of the most dispensed drugs in India.
Indications
- Peptic ulcer disease (duodenal and gastric ulcers)
- Gastro-oesophageal reflux disease (GERD)
- H. pylori eradication (as part of triple/quadruple therapy)
- Zollinger-Ellison syndrome (high-dose PPI)
- NSAID-induced gastropathy (treatment and prophylaxis)
- Stress ulcer prophylaxis in ICU patients
- Erosive oesophagitis
- Non-ulcer dyspepsia
Dosing
Peptic ulcer/GERD: 20 mg once daily before breakfast for 4-8 weeks. H. pylori eradication (triple therapy): Omeprazole 20 mg BD + Amoxicillin 1 g BD + Clarithromycin 500 mg BD for 14 days. Zollinger-Ellison: 60-120 mg/day (divided doses if >80 mg). NSAID prophylaxis: 20 mg once daily. Stress ulcer prophylaxis: 40 mg IV BD. Take 30 minutes before the first meal of the day (active pumps required for drug activation).
Contraindications
- Known hypersensitivity to omeprazole or other PPIs
- Concurrent use with rilpivirine (HIV drug -- requires gastric acid for absorption)
- Concurrent use with nelfinavir
Adverse effects
- Headache, diarrhoea, nausea (common, usually mild)
- Hypomagnesaemia (long-term use; can cause tetany and cardiac arrhythmias)
- Vitamin B12 deficiency (long-term; reduced acid-dependent absorption)
- Clostridium difficile-associated diarrhoea (acid suppression alters gut microbiome)
- Hip and vertebral fractures (long-term use; reduced calcium absorption)
- Community-acquired pneumonia (acid suppression allows bacterial colonisation of stomach)
- Acute interstitial nephritis (rare, idiosyncratic)
- Fundic gland polyps (benign, with chronic use)
- Hypergastrinaemia (compensatory; theoretical concern for carcinoid, but extremely rare in humans)
Drug interactions
- Clopidogrel -- omeprazole inhibits CYP2C19, reducing clopidogrel activation (use pantoprazole or rabeprazole instead if PPI is needed with clopidogrel)
- Methotrexate -- PPIs reduce renal clearance of methotrexate, increasing toxicity
- Azole antifungals (ketoconazole, itraconazole) and iron -- require acidic pH for absorption; PPIs reduce their absorption
- Levothyroxine -- reduced absorption due to increased gastric pH
- Atazanavir, nelfinavir (HIV drugs) -- require acid for absorption; PPIs markedly reduce levels
- CYP2C19 polymorphism -- poor metabolisers have higher omeprazole levels (more common in Asian populations)
Pregnancy and lactation
Category C. Large population studies have not shown increased risk of congenital malformations with first-trimester PPI use. Omeprazole is considered relatively safe in pregnancy when indicated (severe GERD, peptic ulcer). However, some guidelines prefer ranitidine (H2 blocker) as first-line for GERD in pregnancy due to longer safety experience, and recommend PPIs if H2 blockers fail.
Exam-style clinical scenario
A 50-year-old man with a duodenal ulcer tests positive for H. pylori on rapid urease test (CLO test). He has a history of recent coronary stent placement and is on dual antiplatelet therapy (aspirin + clopidogrel). Which PPI should be chosen for H. pylori eradication? Answer: Pantoprazole or rabeprazole should be used instead of omeprazole. Omeprazole and esomeprazole are CYP2C19 inhibitors that reduce the conversion of clopidogrel (a prodrug) to its active metabolite, diminishing its antiplatelet effect and increasing the risk of stent thrombosis. Pantoprazole has the weakest CYP2C19 inhibition among PPIs and is preferred in patients on clopidogrel.
Cost in India
INR 30-70 per strip of 10 capsules (20 mg); IV: INR 40-80 per vial (40 mg)
Clinical governance
Author: MedNext Editorial Team. Clinical reviewer: Awaiting clinical review. Jurisdiction: India (Drugs and Cosmetics Act, 1940). Sources: CIMS India, Indian Pharmacopoeia. Publication state: Awaiting clinical review. Correction: Report errors at support@mednext.academy.
Frequently Asked Questions
Why must PPIs be taken before meals?
PPIs are prodrugs that require activation in an acidic environment (pH <4) near the parietal cell canaliculi. The proton pump (H+/K+ ATPase) is most active during meals when stimulated by histamine, acetylcholine, and gastrin. Taking the PPI 30 minutes before eating ensures that the drug reaches peak plasma concentration coinciding with maximal pump activity, allowing more pump molecules to be irreversibly inhibited.
How does the omeprazole-clopidogrel interaction work?
Clopidogrel is a prodrug that requires two-step hepatic activation, primarily via CYP2C19. Omeprazole is metabolised by and inhibits CYP2C19, reducing the conversion of clopidogrel to its active thiol metabolite. This results in reduced antiplatelet effect (measured by higher platelet reactivity on testing) and a potential increased risk of cardiovascular events in patients with coronary stents. The FDA issued a safety communication advising against the combination.
What is the significance of CYP2C19 polymorphism in PPI therapy?
CYP2C19 metabolises omeprazole. Poor metabolisers (homozygous for non-functional alleles, more common in Asian populations at 12-23%) have higher omeprazole plasma levels and greater acid suppression, leading to higher H. pylori eradication rates. Extensive metabolisers may have subtherapeutic PPI levels with standard doses. Pharmacogenomic testing can guide PPI dosing, though it is not yet routine clinical practice in India.
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