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Omeprazole for PA Students: Indications & Monitoring | Bioavailable

Compound database
Proton pump inhibitors
Omeprazole

OmeprazolePA study guide

Known brand names include Prilosec.

A proton pump inhibitor that sharply lowers stomach acid. It treats GERD and erosive esophagitis, heals duodenal and gastric ulcers, helps clear H. pylori with antibiotics, and controls rare acid-overproducing conditions such as Zollinger-Ellison syndrome.

When to use it

H. pylori infection

Labeled use. With clarithromycin, with or without amoxicillin, in adults with duodenal ulcer disease.

Sources: [1]

Gastroesophageal reflux disease (GERD)

Labeled use. Symptomatic GERD and erosive esophagitis (healing and maintenance), from age 2.

Sources: [1][2][3]

Peptic ulcer disease

Labeled use. Short-term healing of active duodenal ulcer and active benign gastric ulcer in adults.

Sources: [1][2]

When to choose it

PPIs such as omeprazole are more effective than H2 blockers for healing erosive esophagitis and peptic ulcers and are a core part of H. pylori regimens. Choose an H2 blocker or antacid for mild, intermittent heartburn. For patients on clopidogrel, a PPI with less CYP2C19 inhibition, such as pantoprazole, is usually preferred. Reassess the need for long-term therapy regularly.

How it works

Mechanism

Irreversibly blocks the H+/K+ ATPase (proton pump) on the secretory surface of gastric parietal cells, the last step in acid production. It suppresses both basal and stimulated acid secretion, whatever the stimulus. It is cleared mainly by CYP2C19, with a smaller CYP3A4 share.

Sources: [1][2]

Side effects

Why they happen and how to manage them

C. difficile infection: Less stomach acid lets ingested bacteria and spores survive and colonize the gut. Management: Test for C. difficile when diarrhea persists; use the lowest dose for the shortest time.
Hypomagnesemia: Long-term PPI use reduces intestinal magnesium absorption. Management: Check magnesium at baseline and periodically in long-term users or those on digoxin or diuretics; replace magnesium and stop the PPI if needed.
Vitamin B12 deficiency: Food-bound B12 needs acid to be released, so hypo- or achlorhydria impairs absorption. Management: Check B12 when symptoms suggest deficiency after years of use.
Fractures: Possibly reduced calcium absorption with long-term, high-dose acid suppression. Management: Use the shortest course; manage osteoporosis risk per guidelines.
Reduced clopidogrel effect: Omeprazole inhibits CYP2C19, which activates the clopidogrel prodrug. Management: Avoid together; consider another antiplatelet or acid-suppressing option.

Sources: [1][2][3][4][5]

Common and serious

Common

Headache (7%), abdominal pain (5%), nausea and diarrhea (4% each)
Vomiting and flatulence (3% each), constipation, dizziness, rash

Serious

C. difficile-associated diarrhea, especially in hospitalized patients
Acute tubulointerstitial nephritis
Hip, wrist, or spine fractures with high-dose or long-term use
Hypomagnesemia with tetany, arrhythmias, or seizures, usually after prolonged use
Vitamin B12 deficiency with long-term use
Severe skin reactions (SJS, TEN, DRESS) and cutaneous or systemic lupus
Fundic gland polyps with long-term use

Sources: [1][2][3][4][5]

Monitoring

Narrow therapeutic index

The label does not describe a narrow therapeutic index or direct dosing by measured blood levels of the drug.

Sources: [1]

INR (prothrombin time)

Why: Warfarin interaction
When: When omeprazole is started or stopped in a patient on warfarin
Act on: Adjust warfarin to keep INR in the target range
Normal: INR 0.8 to 1.1 when not on a blood thinner. On warfarin, the usual target is 2.0 to 3.0.

Sources: [1][2]

Magnesium

Why: PPI-associated hypomagnesemia
When: Before starting and periodically in prolonged therapy or with digoxin or diuretics
Act on: Replace magnesium; consider stopping the PPI
Normal: 1.7 to 2.2 mg/dL.

Sources: [1][2]

Vitamin B12

Why: Deficiency from long-term acid suppression
When: When symptoms suggest deficiency during long-term use
Normal: 299 to 1054 pg/mL.

Sources: [1][2]

Dosing

Doses come from the FDA label. Study tool, not for clinical decisions.

Adult dose

Active duodenal ulcer: 20 mg once daily for 4 weeks; some patients need another 4 weeks.
H. pylori, triple therapy: Omeprazole 20 mg, amoxicillin 1000 mg, and clarithromycin 500 mg, each twice daily for 10 days. If an ulcer is present, continue omeprazole 20 mg daily for 18 more days.
H. pylori, dual therapy: For 14 days: omeprazole 40 mg once daily with clarithromycin 500 mg three times daily. If an ulcer is present, continue omeprazole 20 mg daily for 14 more days.
Active benign gastric ulcer: 40 mg once daily for 4 to 8 weeks.
Symptomatic GERD: 20 mg once daily for up to 4 weeks.
Erosive esophagitis: Healing: 20 mg once daily for 4 to 8 weeks, with 4 more weeks if no response. Maintenance: 20 mg once daily (studied to 12 months).
Pathologic hypersecretory conditions: Start 60 mg once daily and adjust to need. Split daily doses above 80 mg; doses up to 120 mg three times daily have been used.

Sources: [1]

Renal adjustment

None. Bioavailability rises only slightly in chronic renal impairment, which is not clinically meaningful.

Sources: [1]

Hepatic adjustment

Exposure rises substantially in Child-Pugh A, B, or C. For maintenance of erosive esophagitis healing, use 10 mg once daily. The same reduction applies to Asian patients, who have about four-fold higher exposure.

Sources: [1][2]

Safety

Boxed warning

None on the current label.

Sources: [1]

Contraindications

Known hypersensitivity, including anaphylaxis, to omeprazole, any substituted benzimidazole, or a product component
Use with rilpivirine-containing products
Contraindications of clarithromycin and amoxicillin when given as H. pylori therapy

Sources: [1]

Key interactions

Clopidogrel: CYP2C19 inhibition lowers the active metabolite and its antiplatelet effect. Avoid the combination; consider a different antiplatelet.
Rilpivirine; atazanavir and nelfinavir: Less antiviral exposure and possible resistance. Rilpivirine is contraindicated; avoid atazanavir and nelfinavir.
Warfarin: INR and PT can rise, with bleeding risk. Monitor INR and adjust warfarin.
Citalopram, phenytoin, diazepam, digoxin, tacrolimus: Higher levels of these drugs. Limit citalopram to 20 mg per day; monitor levels or sedation.
High-dose methotrexate: Methotrexate levels may rise and stay high. Consider holding the PPI.
St. John's Wort or rifampin: CYP inducers sharply lower omeprazole levels. Avoid.
Drugs needing stomach acid to absorb (iron salts, ketoconazole, itraconazole, erlotinib, mycophenolate): Reduced absorption.

Sources: [1][2][3][4]

Antidote or reversal

No specific antidote. Treat overdose with symptomatic and supportive care. Omeprazole is highly protein bound, so dialysis does not remove it well.

Sources: [1]

Special populations

Pregnancy

Epidemiologic data do not show more major birth defects or other adverse outcomes with first-trimester use. Well-controlled studies in pregnant women are lacking.

Sources: [1]

Lactation

Limited data suggest omeprazole may pass into breast milk. Effects on the breastfed infant and on milk production are unknown. Weigh breastfeeding benefits against the mother's need for the drug.

Sources: [1]

Pediatric

Established from age 2 to 16 for symptomatic GERD and for healing and maintaining healing of erosive esophagitis. Dose by weight once daily: 10 to under 20 kg, 10 mg; 20 kg and over, 20 mg. Respiratory adverse reactions and fever were the most common in children.

Sources: [1][2][3]

Geriatric

No differences in safety or effectiveness in older adults. Clearance is lower and half-life longer, but no dose adjustment is needed.

Sources: [1]