Omeprazole
5-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole
Also known as: Gastrogard · Prilosec · Ulcergard · Zegerid · H-168/68 · omeprazolum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| GI ulcer management/prevention | 0.5-1 mg/kg PO once daily | PO | q24h | — | 🌎 NA |
| Adjunctive treatment of uremic gastropathy | 0.5-1 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
| Prevent exercise-induced gastritis in racing Alaskan sled dogs | approx. 0.85 mg/kg (one 20 mg tablet) once daily approximately 30 minutes before being fed | PO | q24h | — | 🌎 NA |
| Adjunctive treatment of esophagitis or gastric ulcers | 0.5-1 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
| Gastrinomas or severe esophagitis | 0.7-1.5 mg/kg PO q24h, but if severe esophagitis or gastrinomas may use up to 2 mg/kg PO q12h | PO | q12h-q24h | — | 🌎 NA |
| General GI therapeutics | 0.7 mg/kg PO q24h (20 mg/dog) | PO | q24h | — | 🌎 NA |
| Esophagitis | 0.7 mg/kg PO twice daily | PO | q12h | — | 🌎 NA |
| Adjunctive treatment of uremic vomiting | 0.7 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Helicobacter infection/gastritis | Omeprazole 0.7 mg/kg PO once daily (or an H2 blocker), amoxicillin 15 mg/kg PO twice daily, metronidazole 10 mg/kg PO twice daily, and Pepto Bismol ¼-2 tablets PO twice daily | PO | q24h | 2 weeks | 🌎 NA |
- Adjunctive treatment of uremic gastropathy: Dosage may need to be modified in moderate or severe renal failure.
- Prevent exercise-induced gastritis in racing Alaskan sled dogs: Dosing began approximately 48 hours before exercise.
- Helicobacter infection/gastritis: Other suggestions include omeprazole with either azithromycin 10-20 mg/kg PO once daily or clarithromycin 7.5 mg/kg PO twice daily.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Adjunctive treatment of esophagitis or gastric ulcers | 0.5-1 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
| GI ulcer management/prevention | 0.7-1.5 mg/kg PO q12-24h | PO | q12h-q24h | — | 🌎 NA |
| Adjunctive treatment of uremic gastropathy | 0.7 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
- Adjunctive treatment of uremic gastropathy: Dosage may need to be modified in moderate or severe renal failure.
Ferrets
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Short-term treatment of gastroenteritis | 0.7 mg/kg PO q24h | PO | q24h | Short-term | 🌎 NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of gastric ulcers | 4 mg/kg PO once daily for 4 weeks; to prevent recurrence treat for at least another 4 weeks at 2 mg/kg PO once daily | PO | q24h | 8 weeks total | 🌎 NA |
| Foals: Preventative dose | 1 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
| Foals: Treatment dose | 4 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
| Treatment or prophylaxis of gastric ulcers in foals | 4 mg/kg PO once daily for treatment, 1-2 mg/kg PO once daily for prophylaxis | PO | q24h | — | 🌎 NA |
| Foals: Gastric ulcers | 4 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
- Treatment of gastric ulcers: ARCI UCGFS Class 5 Drug
- Foals: Preventative dose: There has been a recent shift to not administering prophylactic antiulcer medication routinely to sick foals.
- Foals: Treatment dose: Will reduce gastric pH in a few hours.
- Foals: Gastric ulcers: Commonly foals will be started on ranitidine (1.5 mg/kg IV q8h; 6.6 mg/kg PO q8h) and omeprazole together.
Swine
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Ulcer management | 40 mg of PO daily for two days; fasted for 48 hours | PO | q24h | 2 days | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Omeprazole is a highly effective proton pump inhibitor (PPI) widely used in veterinary medicine for the treatment and prevention of gastroduodenal ulcers and erosions.
- Superior Efficacy: It is generally considered superior to H2-receptor antagonists (such as famotidine) for raising gastric pH and preventing exercise-induced gastritis, as demonstrated in racing Alaskan sled dogs.
- Equine Use: An oral paste formulation is specifically labeled and highly effective for the treatment and prevention of gastric ulcers in horses (EGUS).
- Broad Application: It is utilized across multiple species, including dogs, cats, ferrets, and swine, to manage conditions like uremic gastropathy, esophagitis, Helicobacter infections, and NSAID/corticosteroid-induced ulceration.
Clinical Pearl: Because omeprazole requires an acidic environment for activation but is degraded by stomach acid before absorption, human oral formulations are enteric-coated. These must not be crushed or chewed, as this will destroy the drug's bioavailability.
Mechanism of action
Omeprazole is a prodrug that acts as a substituted benzimidazole gastric acid pump inhibitor.
- Absorption & Distribution: After absorption, it diffuses from the blood into the highly acidic secretory canaliculi of the gastric parietal cells.
- Activation: In this acidic environment (pH < 3), it is protonated and rearranged into its active form, a sulphenamide derivative.
- Irreversible Binding: The active sulphenamide binds irreversibly via disulfide bonds to the H⁺/K⁺ ATPase enzyme (the proton pump) at the secretory surface.
- Acid Suppression: This blocks the final common pathway of gastric acid secretion, inhibiting the transport of hydrogen ions into the stomach lumen during both basal and stimulated conditions.
Pharmacological Note: Because the binding is irreversible, acid secretion only resumes when new H⁺/K⁺ ATPase enzymes are synthesized. This explains why its duration of action (24-72 hours) far outlasts its short plasma half-life (~1 hour). Omeprazole also inhibits the hepatic cytochrome P-450 mixed-function oxidase system, which can lead to drug interactions.
Safety & warnings
Contraindications
- Known hypersensitivity to omeprazole
Adverse effects
- GI distress (anorexia, colic, nausea, vomiting, flatulence, diarrhea)
- Hematologic abnormalities (rare)
- Urinary tract infections
- Proteinuria
- CNS disturbances
- Urticaria (rare in horses)
Precautions
Use with caution in patients with severe hepatic or renal disease, as the drug's half-life may be prolonged and dosage adjustment may be necessary. Safety during pregnancy is not fully established (FDA Category C); high doses in lab animals showed embryo-lethality. Nursing is discouraged due to potential adverse effects in infants and tumorigenicity seen in rat studies. Chronic very high doses in rats caused enterochromaffin-like cell hyperplasia and gastric carcinoid tumors, though the clinical significance for standard veterinary use (e.g., 4 weeks in dogs, 90 days in horses) is believed to be low.
Drug interactions
Omeprazole may potentially alter benzodiazepine metabolism and prolong CNS effects
Increased levels of omeprazole, clarithromycin and 14-hydroxyclarithromycin are possible
Omeprazole may decrease oral absorption
Omeprazole may reduce cyclosporine metabolism
Omeprazole increases gastric pH, which may decrease the absorption of these drugs that require an acidic environment
Omeprazole may increase anticoagulant effect
Monitoring
- Clinical efficacy (resolution of clinical signs of ulcers/esophagitis)
- Adverse effects (GI distress)
- Liver enzymes (may increase)
- Serum gastrin levels (will increase early in therapy)
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed from the gut. The human commercial product is in an enteric-coated granule form as the drug is rapidly degraded by stomach acid. The equine paste is not enteric coated. In humans, peak serum levels occur within 0.5-3.5 hours and onset of action within 1 hour.
Distribution
Distributed widely, but primarily concentrates in gastric parietal cells. In humans, approximately 95% is bound to albumin and alpha1-acid glycoprotein. It is unknown whether omeprazole enters maternal milk.
Metabolism
Extensively metabolized in the liver via the cytochrome P-450 mixed function oxidase system to at least six different metabolites. Significant hepatic dysfunction will reduce the first pass effect of the drug.
Elimination
Metabolites are excreted principally in the urine, but also via the bile into feces.
Overdose
The LD50 in rats after oral administration is reportedly >4 grams/kg. Humans have tolerated oral dosages of 360 mg/day without significant toxicity.
Should a massive overdose occur, treat symptomatically and supportively. Due to its wide safety margin, acute toxicity from accidental ingestion is generally mild.
Available products
Formulations
- Oral paste
- Delayed-release capsules (enteric-coated)
- Delayed-release tablets (enteric-coated)
- Powder for oral suspension (with sodium bicarbonate)
- Immediate-release capsules (with sodium bicarbonate)
Veterinary
- Omeprazole Oral Paste, 2.28 g per syringe; Gastrogard® (Merial), (Rx)
- Omeprazole Oral Paste, 2.28 g per syringe; Ulcergard® (Merial), (OTC)
Human-labeled
- Omeprazole Oral Delayed-Release Capsules: 10 mg, 20 mg & 40 mg; Prilosec®
- Omeprazole Oral Delayed-Release Tablets: 20 mg; Prilosec® OTC
- Omeprazole/Sodium Bicarbonate Oral Capsules (Immediate Release): 20 mg or 40 mg omeprazole with 1,100 mg sodium bicarbonate; Zegerid®
- Omeprazole/Sodium Bicarbonate Powder for Oral Suspension: 20 mg or 40 mg omeprazole with 1,680 mg sodium bicarbonate; Zegerid®
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Omeprazole oral paste should be stored below 86°F (30°C). Transient exposure to temperatures up to 104°F is permitted. Omeprazole tablets/capsules should be stored at room temperature in light-resistant, tight containers. Omeprazole pellets found in the capsules are fragile and should not be crushed.
Client information
- Timing is crucial: Give this medication on an empty stomach, preferably in the morning, about 30 to 60 minutes before a meal. The drug needs active proton pumps to work, which are stimulated by eating.
- Do not crush or chew: If using human capsules or tablets, they are specially coated to survive stomach acid. Crushing or chewing them will destroy the medication before it can be absorbed.
- If you must open a capsule to give the pellets, mix them gently with a small amount of fruit juice (not water, milk, or saline) and give immediately without crushing the pellets.
- Contact your veterinarian if your pet experiences persistent vomiting, diarrhea, or loss of appetite.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.