Omeprazole

- Proton pump inhibitor
- Substituted benzimidazole compound
- Acid labile, so available as enteric-coated pellets for release in alkaline medium of intestine

 

 

Mechanism of Action

Inhibits H+ K+ ATPase
- Inhibits exchange of K+ ions for H+ ions ('acid pump')
- Inhibits gastric acid secretion irrespective of the stimulus

 

Actions

- Inhibits gastric acid secretion (upto 100%)
- Inhibits pepsin activity
- Inhibitory effect lasts upto 72 hours

Pharmacokinetics

- Well absorbed after oral administration
- High affinity for acidic enviroment of parietal cells
- Almost completely metabolised by the liver
- Half life 0.5-3 hours

Indications

- Peptic Ulcer
Gastric, Duodenal
- Gastro Oesophageal Reflux Disease (GORD/GERD)
- Zollinger Ellison Syndrome
- Acid aspiration syndrome

Omeprazole in peptic ulcer

- Potent gastric acid inhibition
- Earlier symptom relief than H2 antagonists
- Higher clinical cure rates (» 95%) and lesser relapses than with H2 antagonists
- May be administered with antibacterials and nitroimidazoles to tackle H.pylori infection
- Safe for long term administration (> 5 years)

Omeprazole in GERD

- Reduced gastric acidity decreases harmful effects of acid on oesophageal mucosa
- May be administered alone or with prokinetic agents as necessary
- Superior to H2 antagonists

Omeprazole in other conditions

- May be employed in situations where acid inhibition is desired e.g., with NSAIDs, prophylaxis of acid aspiration syndrome, Zollinger Ellison syndrome
- Superior efficacy to other drug categories

Dosage
Usual dosage20 mg daily

Peptic Ulcer & GERD
Initial
20 - 40 mg daily for 4-8 weeks
Maintenance
10 - 20 mg daily

Zollinger Ellison Syndrome
60 mg per day initially increased to 120 mg t.i.d.

 

Adverse Effects

- Well tolerated
- GI, CNS and skin-related adverse effects are commoner, e.g., diarrhoea, rash, headache
- Prolongs elimination of diazepam, warfarin, phenytoin
- Safety in children, pregnancy not established

 

Comparison with H2 blockers

- Omeprazole acts at final stage of acid secretion irrespective of the stimulus; H2 blockers inhibit histamine dependant acid secretion only
- Omeprazole is a more potent acid inhibitor
- Earlier symptom relief and better cure rates with omeprazole

Comparison with newer proton pump inhibitors

- Omeprazole is time tested and more widely documented than newer agents
- No major advantages in terms of overall patient benefits
- Newer agents may be needlessly expensive

 

Salient Features

- Potent acid inhibitor; greater inhibition than H2 antagonists
- Acts on the final stage of acid secretion irrespective of the stimulus
- Useful in peptic ulcer, GERD and in other situations warranting gastric acid suppression
- Earlier symptom relief, higher success rates and lower relapse rates than H2 antagonists
- Wider experience and better documentation than newer proton pump inhibitors
- Well tolerated and safe for long term administration