omeprazole
Losec ◆, Prilosec

Available forms
Available by prescription only
Capsules (delayed-release): 10 mg, 20 mg, 40 mg

Indications and dosages
 Active duodenal ulcer. Adults: 20 mg P.O. daily for 4 to 8 weeks.
 Helicobacter pylori eradication to reduce risk of duodenal ulcer recurrence.
Triple therapy Adults: 20 mg P.O. b.i.d. plus 500 mg clarithromycin P.O. b.i.d. plus 1,000 mg amoxicillin P.O. b.i.d. for 10 days. For patients with an ulcer present at the time that therapy starts, an additional 18 days of omeprazole 20 mg once daily is recommended alone for ulcer healing and symptom relief. (Also see entries for clarithromycin and amoxicillin.)
Dual therapy Adults: 40 mg P.O. q morning plus 500 mg clarithromycin P.O. t.i.d. for 14 days followed by 14 days of omeprazole 20 mg daily. (Also see entry for clarithromycin.)
 Severe erosive esophagitis; symptomatic, poorly responsive gastroesophageal reflux disease (GERD). Adults: 20 mg P.O. daily for 4 to 12 weeks. Patients with GERD should have failed initial therapy with an H₂ antagonist. May continue with maintenance dosage of 20 mg daily for up to 1 year.
 Pathologic hypersecretory conditions (such as Zollinger-Ellison syndrome). Adults: Initial dosage is 60 mg P.O. daily; adjust dosage based on patient response. Administer daily doses exceeding 80 mg in divided doses. Doses up to 120 mg t.i.d. have been administered. Continue therapy as long as clinically indicated.
 Gastric ulcer. Adults: 40 mg P.O. daily for 4 to 8 weeks.
≡ Dosage adjustment. Patients with hepatic impairment may need dosage adjustments. Asian patients may need dosage adjustments because of increased bioavailability of drug in this population.

Pharmacodynamics
Antisecretory action: Omeprazole inhibits the activity of the acid (proton) pump, H⁺/K⁺ adenosine triphosphatase (ATPase), located at the secretory surface of the gastric parietal cell. This blocks the formation of gastric acid.

Pharmacokinetics
Absorption: Omeprazole is acid-labile, and the formulation contains enteric-coated granules that permit absorption after drug leaves the stomach. Absorption is rapid. Bioavailability is about 40% because of instability in gastric acid as well as a substantial first-pass effect. Bioavailability increases slightly with repeated dosing, possibly because of drug’s effect on gastric acidity.
Distribution: About 95% protein-bound.
Metabolism: Primarily metabolized in the liver.
Excretion: Primarily excreted by the kidneys. Plasma half-life is 1/2 to 1 hour, but drug effects may persist for days.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug or its components.

Interactions
Drug-drug. Ampicillin esters, iron derivatives, itraconazole, ketoconazole: Causes poor bioavailability because optimal absorption of these drugs requires a low gastric pH. Avoid use together.
Diazepam, phenytoin, propranolol, theophylline, warfarin: May impair effects of these drugs. Monitor patient closely for decreased effect or toxicity.
Drug-herb. Male fern: Inactivates in alkaline environments. Discourage use together.
Pennyroyal: May change the rate at which toxic metabolites of pennyroyal form. Discourage use together.

Adverse reactions
CNS: headache, dizziness, asthenia.
GI: diarrhea, abdominal pain, nausea, vomiting, constipation, flatulence.
Musculoskeletal: back pain.
Respiratory: cough, upper respiratory tract infection.
Skin: rash.

Effects on lab test results
None reported.

Overdose and treatment
Reports of overdose are rare. Symptoms include confusion, drowsiness, blurred vision, tachycardia, nausea, vomiting, diaphoresis, dry mouth, and headache. Doses up to 360 mg daily have been well tolerated.
 Treatment should be symptomatic and supportive. Dialysis is of little value because of the extent of binding to plasma proteins.

Special considerations
• Drug increases its own bioavailability with repeated administration. It’s labile in gastric acid; less of it is lost to hydrolysis because drug elevates gastric pH.
• Capsules shouldn’t be crushed.
• If administered through a feeding tube, an acidic fluid such as orange juice may decrease risk of clogging tube.
• Serum gastrin levels rise in most patients during first 2 weeks of therapy.
• Monitor liver function tests in patients with hepatic impairment.
Breast-feeding patients
• It isn’t known if drug appears in breast milk. Patient should avoid breast-feeding during therapy.
Pediatric patients
• Safety in children hasn’t been established.

Patient education
• Explain importance of taking drug exactly as prescribed.
• Tell patient to take 30 minutes before meals and not to crush capsules.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use