Drug reference

Omeprazole

Proton Pump Inhibitor · Antiulcer

Also known as Omeprazole Magnesium, Omeprazole Sodium

START

20 mg PO once daily, 30 min before breakfast

TYPICAL MAX

40 mg BID (Zollinger-Ellison)

STOP IF

Hypersensitivity

WATCH

Mg²⁺ · B12 · C. difficile risk on long use

CDSCO approvedJan AushadhiNPPA price-controlledATC A02BC01

Dose laddermg/d

Renal dose adjustmenteGFR mL/min/1.73m²

KDIGO 2024 + manufacturer label

Pharmacokineticsplasma · t hours

ONSET: 1h · acid suppression begins
PEAK: 2h · Cmax
t½: 1h · plasma t½ (effect outlasts)
DURATION: 1d · irreversible H⁺/K⁺ ATPase block

EXCRETION

CYP2C19 + CYP3A4 · 80% renal metabolites

route + CYP

INTERACTIONS

12 major

SEVERE in our sources

PREGNANCY

Category C — pantoprazole preferred when possible

FDA category + note

Top interactionssee all 12 →

FluoxetineSevereTextbookG&G 14e · p1592
RifampinSevereTextbookG&G 14e · p1592
AcalabrutinibSevereDatabaseDDInter
AtazanavirSevereDatabaseDDInter

Available in India

1,694 branded formulations and 1,901 fixed-dose combinations. Look up specific brands in the Drugs workspace.

Jan Aushadhi — generic available at GoI pharmacies

Mechanism

Omeprazole is an irreversible proton pump inhibitor. It binds covalently to the H+/K+-ATPase enzyme system (the proton pump) found on the secretory surface of parietal cells in the stomach. This action blocks the final step of acid production, leading to a profound and long-lasting inhibition of gastric acid secretion.

Indications

Gastroesophageal Reflux Disease (GERD)Erosive EsophagitisDuodenal UlcerGastric UlcerHelicobacter pylori eradication (in combination with antibiotics)Zollinger-Ellison SyndromePrevention of NSAID-induced gastric ulcersStress ulcer prophylaxis (off-label)heartburnGastric ulcersDuodenal ulcersGastroesophageal reflux diseaseHelicobacter pylori eradicationPathological hypersecretory conditionsReducing the risk of duodenal ulcer recurrence associated with H. pylori infectionsSelf-treatment of acid reflux (over-the-counter)Peptic ulcer (duodenal, gastric, NSAID-induced)Bleeding peptic ulcerStress ulcers (prophylaxis)Systemic mastocytosisEndocrine adenomas (other gastric hypersecretory states)Aspiration pneumonia (prophylaxis)

Dosing

Adult: GERD: 20 mg PO once daily for 4-8 weeks. Erosive Esophagitis: 20 mg PO once daily for 4-8 weeks, can increase to 40 mg once daily if needed. Duodenal Ulcer: 20 mg PO once daily for 2-4 weeks. Gastric Ulcer: 20 mg PO once daily for 4-8 weeks. H. pylori eradication: 20 mg PO twice daily (or 40 mg once daily) with appropriate antibiotics for 7-14 days.…
Pediatric: GERD (children ≥1 year, weighing ≥10 kg): 0.7-1.4 mg/kg once daily, max 20 mg/day for 1-16 years. Dosing varies by weight: 10-20 kg: 10 mg once daily; >20 kg: 20 mg once daily.
Renal adjustment: No dose adjustment is necessary for patients with renal impairment.
Hepatic adjustment: In patients with severe hepatic impairment, the dose should not exceed 20 mg once daily.
Geriatric: No specific dose adjustment is generally required, but consider monitoring for potential increased risk of adverse effects, especially with long-term use.
Max dose: Typically 40 mg/day for most standard indications. Up to 360 mg/day (divided doses) for Zollinger-Ellison Syndrome.

Pharmacokinetics

Onset

Within 1 hour.

Peak effect

Plasma concentration: 0.5-3.5 hours. Maximum acid suppression: 2 hours.

Duration

Acid suppression up to 72 hours, despite short plasma half-life.

Half-life

0.5 to 1 hour (plasma elimination half-life).

Bioavailability

30-40% initially, increases to approximately 65% with repeated administration.

Protein binding

Approximately 95%.

Metabolism

Extensively metabolized in the liver, primarily by CYP2C19 (S-omeprazole) and CYP3A4 (R-omeprazole).

Excretion

Approximately 80% renally excreted and 20% excreted via feces.

Contraindications

Hypersensitivity to omeprazole or other substituted benzimidazoles
Concomitant use with nelfinavir (due to significant reduction in nelfinavir plasma concentrations)

Side effects

Common

HeadacheNauseaDiarrheaAbdominal painFlatulenceVomitingDizzinessRashConstipationLoose stoolsMuscle and joint pain

Serious

Clostridioides difficile-associated diarrhea (CDAD)
Osteoporosis-related fractures (with long-term high-dose use)
Hypomagnesemia (with prolonged use, often >3 months)
Acute interstitial nephritis
Cutaneous and systemic lupus erythematosus (new onset or exacerbation)
Vitamin B12 deficiency (with prolonged use, >2-3 years)
Fundic gland polyps (with long-term use)
Subacute myopathy
Arthralgias
Interstitial nephritis
Pharyngitis
Skin rashes
Increased risk of bone fracture
Increased susceptibility to hospital-acquired pneumonia
Increased susceptibility to community-acquired Clostridium difficile infection
Increased susceptibility to spontaneous bacterial peritonitis (in patients with ascites)
Hypomagnesemia
Vitamin B12 (cobalamin) deficiency (with long-term use, >3 years)
Hypergastrinemia leading to ECL hyperplasia and fundic gland polyposis
Atrophic gastritis
Rashes (1.5% incidence)
Leucopenia (infrequent)
Hepatic dysfunction (infrequent)
Atrophic gastritis (occasionally on prolonged treatment)
Gynaecomastia (on prolonged use)
Erectile dysfunction (on prolonged use)
Accelerated osteoporosis (among elderly patients with high-dose long-term use for GERD)

Pregnancy & lactation

Pregnancy

Category C — pantoprazole preferred when possible

Lactation

Omeprazole is excreted in human milk. Although adverse effects on breastfed infants are not expected with typical maternal doses, caution is advised.

Drug interactions

Fluoxetine

Severe

Textbook

omeprazole AUC increased 7.1-fold.

coadministration generally contraindicate[d] or at least require[s] dosage adjustment.

Source: G&G 14e · p1592

Rifampin

Severe

Textbook

omeprazole AUC decreased by 93% (AUCR 0.07).

coadministration generally contraindicate[d] or at least require[s] dosage adjustment.

Source: G&G 14e · p1592

Acalabrutinib

Severe

Database

Drug interaction classified as: absorption

Source: DDInter

Atazanavir

Severe

Database

Substantially reduced atazanavir concentrations, leading to loss of antiviral effectiveness.

Proton pump inhibitors should be avoided in patients receiving atazanavir without ritonavir.

Source: DDInter

Cilostazol

Severe

Database

Increased plasma concentrations of cilostazol and its active metabolites, potentially increasing the risk of adverse effects (e.g., headache, diarrhea, palpitations).

Consider reducing the cilostazol dose by half when co-administered with omeprazole. Monitor for adverse effects.

Source: DDInter

Citalopram

Severe

Database

Slight increase in QT prolongation risk.

Max citalopram 20mg with omeprazole. Monitor ECG.

Source: DDInter

Clopidogrel

Severe

Database

Lower efficacy of clopidogrel.

Consider avoiding coadministration or using an alternative proton pump inhibitor or antiplatelet agent.

Source: DDInter

Dacomitinib

Severe

Database

Clinical effect not specified

Source: DDInter

Dasatinib

Severe

Database

Source: DDInter

Erlotinib

Severe

Database

Reduced plasma levels and potentially reduced efficacy of erlotinib.

Source: DDInter

Methotrexate

Severe

Database

Increased methotrexate levels, potentially leading to toxicity.

Not specified, but typical management involves monitoring methotrexate levels.

Source: DDInter

Nelfinavir

Severe

Database

Reduced plasma concentrations of nelfinavir, leading to decreased antiviral efficacy and potential for viral resistance.

Avoid concomitant use. If a PPI is essential, consider an alternative antiretroviral or an alternative acid-suppressing agent (e.g., H2RA with careful timing, or antacids with separation).

Source: DDInter