Omeprazole: Uses, Dosage, Side Effects, and More
1. Drug Name
Generic Name: Omeprazole
Brand Name(s):
- Pakistan: Omez, Risek
- India: Omez, Lomac
- United States: Prilosec
- United Kingdom: Losec, Mepradec
2. Pharmacological Class
Class: Proton Pump Inhibitor (PPI)
Subclass: Benzimidazole
3. Mechanism of Action
Omeprazole works by irreversibly inhibiting the H+/K+ ATPase enzyme system (the proton pump) of the gastric parietal cells. This action blocks the final step of acid production in the stomach, leading to a reduction in gastric acidity.
4. Indications
Primary Indications:
- Gastroesophageal reflux disease (GERD)
- Peptic ulcer disease
- Zollinger-Ellison syndrome
- Erosive esophagitis
Off-label Uses:
- Prevention of upper gastrointestinal bleeding in critically ill patients
5. Dosage and Administration
Standard Dosage:
- GERD: 20 mg once daily for 4-8 weeks.
- Peptic Ulcer Disease: 20-40 mg once daily for 4-8 weeks.
- Zollinger-Ellison Syndrome: 60 mg once daily, dosage may be adjusted based on patient response.
Route of Administration: Oral
Special Populations:
- Pediatric: Dosage should be individualized based on weight and age.
- Geriatric: No specific dose adjustments, but caution is advised due to increased risk of side effects.
6. Pharmacokinetics
Absorption: Rapidly absorbed, with peak plasma levels occurring within 0.5 to 3.5 hours.
Distribution: Widely distributed, with approximately 95% bound to plasma proteins.
Metabolism: Extensively metabolized in the liver, primarily by the CYP2C19 and CYP3A4 enzymes.
Excretion: Primarily excreted in urine (80%), with the remainder in feces.
Half-life: Approximately 0.5 to 1 hour, but the acid suppression effect lasts up to 72 hours due to irreversible binding to the proton pump.
7. Contraindications
Omeprazole is contraindicated in patients with:
- Hypersensitivity to omeprazole or any of its components.
- Concurrent use with nelfinavir.
8. Warnings and Precautions
Use caution in patients with:
- Severe hepatic impairment.
- Risk factors for osteoporosis-related fractures.
- Long-term use which may lead to vitamin B12 deficiency.
- Clostridium difficile-associated diarrhea.
Monitor magnesium levels before and during treatment if on long-term therapy or concomitant medications that cause hypomagnesemia.
9. Side Effects
Common Side Effects:
- Headache
- Nausea
- Diarrhea
- Abdominal pain
Serious Side Effects:
- Acute interstitial nephritis
- Bone fracture
- Clostridium difficile infection
- Hypomagnesemia
10. Drug Interactions
Major Interactions:
- Nelfinavir (decreased effectiveness)
- Clopidogrel (reduced antiplatelet effect)
Moderate Interactions:
- Warfarin (increased risk of bleeding)
- Diazepam (increased levels)
Minor Interactions:
- St. John's Wort (reduced effectiveness)
- Antacids (may decrease absorption)
11. Pregnancy and Lactation
Pregnancy Category: C
Breastfeeding Considerations: Omeprazole is excreted in breast milk, but its effects on the infant are unknown. Use only if clearly needed and the benefits outweigh the risks.
12. Patient Counseling Information
Key Points for Patients:
- Take omeprazole exactly as prescribed, usually before meals.
- Do not crush or chew the tablets; swallow them whole.