# Omeprazole: veterinary dose and monograph

> Omeprazole is a veterinary gastrointestinal drug. Proton pump inhibitor (PPI). Indications include gastric / duodenal ulceration (NSAID-induced, stress, Helicobacter); gastro-oesophageal reflux disease (GERD); hypergastrinaemia (gastrinoma, mast cell tumour with gastrin release). This monograph lists 6 reference doses for dogs, cats, horses and ferrets, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/omeprazole · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Gastrointestinal
- **Also known as:** Prilosec, GastroGard, UlcerGard, Losec
- **Species with doses:** Dogs, Cats, Horses and Ferrets
- **General dose range:** 1–4 mg/kg PO q24h — check the species tables for the indication
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Gastric / duodenal ulceration (NSAID-induced, stress, Helicobacter)
- Gastro-oesophageal reflux disease (GERD)
- Hypergastrinaemia (gastrinoma, mast cell tumour with gastrin release)
- Equine gastric ulcer syndrome (EGUS) — both squamous and glandular
- Prevention of stress ulcers in critical-care patients
- Adjunct to Helicobacter eradication (with amox + metronidazole)

## Omeprazole dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Omeprazole doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Gastric ulcer / GERD | 1–2 mg/kg | PO | q12–24h | 4–8 weeks |
| Prevention (NSAID co-administration, stress) | 1 mg/kg | PO | q24h | — |

- Gastric ulcer / GERD: Papich 5e: 1–2 mg/kg (or 20 mg per dog) q24h PO; q12h gives more consistent acid suppression. Plumb’s p.907: 0.5–1 mg/kg q24h (Davenport; Trepanier); oesophagitis 0.7 mg/kg twice daily (Simpson); severe oesophagitis or gastrinoma up to 2 mg/kg q12h (Willard). Give 30–60 min before food.
- Prevention (NSAID co-administration, stress): Plumb’s p.907: 0.5–1 mg/kg PO once daily; sled dogs about 0.85 mg/kg (20 mg) daily starting 48 h before exercise (Williamson). Papich 5e: 1–2 mg/kg q24h.

### Cats

*Omeprazole doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Gastric ulcer / oesophagitis | 0.5–1.5 mg/kg | PO | q12–24h | 4–8 weeks |

- Gastric ulcer / oesophagitis: Papich 5e: 1 mg/kg q24h PO (q12h for more consistent suppression). Plumb’s p.907: 0.5–1 mg/kg q24h (Sellon; Trepanier); 0.7–1.5 mg/kg q12–24h (Willard); uraemic gastropathy 0.7 mg/kg q24h (Vaden).

### Horses

*Omeprazole doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| EGUS treatment (GastroGard) | 4 mg/kg | PO | q24h | 4 weeks, then 2 mg/kg daily for ≥4 weeks to prevent recurrence |
| EGUS prevention (UlcerGard, racehorses) | 1 mg/kg | PO | q24h | — |

- EGUS treatment (GastroGard): Papich 5e and Plumb’s p.907 (GastroGard label): 4 mg/kg PO once daily for 4 weeks, then at least 4 more weeks at 2 mg/kg to prevent recurrence; twice daily may help non-responders; 1–2 mg/kg may be as effective (Papich). Foals: treatment 4 mg/kg, prophylaxis 1–2 mg/kg q24h. Re-scope before stopping. ARCI Class 5.
- EGUS prevention (UlcerGard, racehorses): Papich 5e: prevention 1–2 mg/kg q24h PO (1 mg/kg was effective in studies). Plumb’s p.907: foal prophylaxis 1–2 mg/kg once daily (Wilkins; Stewart).

### Ferrets

*Omeprazole doses for ferrets*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Helicobacter mustelae (triple therapy) | 0.7 mg/kg | PO | q24h | — |

- Helicobacter mustelae (triple therapy): Plumb's (Fisher 2005): omeprazole 0.7 mg/kg PO once daily as the acid-suppression component of Helicobacter mustelae triple therapy with amoxicillin + clarithromycin/metronidazole ×14–21 days.

## Contraindications

Known hypersensitivity. Long-term use (>1–2 months) — emerging evidence of microbiome disruption, magnesium / B12 deficiency, fracture risk (extrapolated from human studies). Discontinuation should be TAPERED in patients on >1 month therapy — rebound hyperacidity reported. Caution in severe hepatic impairment.

## Species-specific warnings

> **Caution:** Dogs: q12h dosing more effective than q24h for severe ulceration. Taper after >1 month. Switch to famotidine if on clopidogrel.

> **Caution:** Cats: Cats tolerate omeprazole well. Compound to flavoured suspension if compliance poor.

> **Caution:** Horses: GastroGard is the ONLY FDA-approved equine ulcer treatment. Treatment dose 4 mg/kg PO q24h × 4 wk; re-scope at 4 wk.

## Adverse effects

- GI: occasional diarrhoea, flatulence, anorexia
- Hypomagnesaemia on chronic use (>3 months)
- Possible vitamin B12 malabsorption on chronic use
- Rebound hyperacidity on abrupt discontinuation after long courses
- Rare hepatotoxicity (mild ALT elevation)
- Drug interactions via CYP2C19 inhibition (clopidogrel, warfarin, diazepam)

## Drug interactions

- Clopidogrel: omeprazole inhibits CYP2C19 — reduces clopidogrel activation, blunts antiplatelet effect (clinically important in cardiology patients)
- Diazepam, phenytoin, warfarin: omeprazole inhibits CYP2C19 — prolongs effect
- Sucralfate: requires acidic gastric environment — separate by 2 h (give sucralfate first)
- Ketoconazole, itraconazole: require acidic gastric pH for absorption — efficacy reduced
- Iron salts, calcium carbonate: reduced absorption in alkalinised stomach
- Antiplatelet / NSAID combinations: omeprazole is the PROTECTIVE drug, but check clopidogrel interaction

## Pregnancy and lactation

Crosses placenta. FDA Category C (human). Generally avoided in pregnancy unless clinically essential. Limited veterinary data — used in pregnant mares with EGUS at standard dose.

## Monitoring

- Clinical response — improvement expected within 7–14 days
- Repeat gastroscopy at 4–8 weeks (equine EGUS) to confirm healing
- Magnesium and B12 on chronic courses (>3 months)
- Concurrent clopidogrel — switch to famotidine if antiplatelet therapy essential
- Taper after >1 month therapy — abrupt discontinuation = rebound hyperacidity

## Toxicity and overdose

Very wide therapeutic index. Acute high-dose: GI upset, mild ataxia. Chronic (>3 months): hypomagnesaemia, B12 malabsorption, microbiome disruption (Clostridium difficile risk extrapolated from human data). Rebound hyperacidity on abrupt discontinuation.

Management: Supportive — most overdoses asymptomatic. Activated charcoal if recent large ingestion. Monitor electrolytes (Mg, Ca). No specific antidote needed.

## Clinical pearls

- Dogs / cats: 1 mg/kg PO q12h is more effective than q24h for severe ulceration
- Equine EGUS: 4 mg/kg PO q24h × 4 weeks then re-scope; UlcerGard 1 mg/kg PO q24h for prevention in racehorses
- Give on EMPTY STOMACH 30 min before first meal — food reduces bioavailability by 50%
- Onset: takes 3–5 days for steady-state acid suppression; combine with sucralfate or H2-blocker for immediate effect
- Taper after long courses (>1 month) — taper over 1–2 weeks to avoid rebound hyperacidity
- NSAID + glucocorticoid combinations: never do this; if essential, add omeprazole + misoprostol
- Clopidogrel patients (HCM with ATE risk): use famotidine instead — omeprazole blunts clopidogrel activation

## Mechanism of action

Substituted benzimidazole proton pump inhibitor (PPI). Pro-drug — acid-activated in the parietal cell canaliculus to a reactive sulfenamide that COVALENTLY binds the H⁺/K⁺-ATPase (proton pump), irreversibly inhibiting gastric acid secretion. Suppression lasts until new pumps are synthesised (24–72 h). Steady-state requires 3–5 days. More potent and longer-lasting acid suppression than H2-blockers.

## Formulations and products

- GastroGard oral paste 370 mg/g (equine; 2.28 g omeprazole per syringe — Plumb’s p.908; Papich 5e p.670)
- UlcerGard oral paste 370 mg/g (equine prevention)
- Prilosec OTC 20 mg human tablet
- Losec / Omez 20 mg capsule
- Omeprazole sodium 40 mg dry-powder vial (IV; label-sourced — not in Papich 5e or Plumb’s; reconstitute per label)
- GastroGard (Merial / Boehringer) — 370 mg/g paste; 2.28 g omeprazole per syringe, Oral paste (equine)
- UlcerGard (Merial / Boehringer) — 370 mg/g, Oral paste (equine prevention)
- Prilosec — 20 / 40 mg, Delayed-release capsule (human-label)
- Omez — 20 mg, Capsule (human-label)
- Losec — 10 / 20 / 40 mg, Tablet / capsule (human-label)

## Storage

Capsules / tablets: 15–30 °C, dry, protected from MOISTURE (omeprazole degrades in moisture). Paste: 15–25 °C. IV reconstituted solution: refrigerate, use within 4 h.

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

## Other gastrointestinal drugs

- [Metronidazole](https://vetmasterji.com/drugs/metronidazole)
- [Mineral Oil (Liquid Paraffin)](https://vetmasterji.com/drugs/mineral-oil)
- [Mirtazapine](https://vetmasterji.com/drugs/mirtazapine)
- [Misoprostol](https://vetmasterji.com/drugs/misoprostol)
- [Pantoprazole](https://vetmasterji.com/drugs/pantoprazole)
- [Ranitidine](https://vetmasterji.com/drugs/ranitidine)
- [S-Adenosylmethionine (SAMe)](https://vetmasterji.com/drugs/sam-e)
- [Silymarin (Milk Thistle / Silybin)](https://vetmasterji.com/drugs/silymarin)

## Frequently asked questions

### What is the dose of Omeprazole for dogs?

Reference doses for Omeprazole in dogs: 1–2 mg/kg PO q12–24h for 4–8 weeks (Gastric ulcer / GERD); 1 mg/kg PO q24h (Prevention (NSAID co-administration, stress)). Confirm against the label and the patient before use.

### What is the dose of Omeprazole for cats?

Reference doses for Omeprazole in cats: 0.5–1.5 mg/kg PO q12–24h for 4–8 weeks (Gastric ulcer / oesophagitis). Confirm against the label and the patient before use.

### What is the dose of Omeprazole for horses?

Reference doses for Omeprazole in horses: 4 mg/kg PO q24h for 4 weeks, then 2 mg/kg daily for ≥4 weeks to prevent recurrence (EGUS treatment (GastroGard)); 1 mg/kg PO q24h (EGUS prevention (UlcerGard, racehorses)). Confirm against the label and the patient before use.

### When should Omeprazole not be used?

Known hypersensitivity. Long-term use (>1–2 months) — emerging evidence of microbiome disruption, magnesium / B12 deficiency, fracture risk (extrapolated from human studies). Discontinuation should be TAPERED in patients on >1 month therapy — rebound hyperacidity reported. Caution in severe hepatic impairment.

### What are the side effects of Omeprazole in animals?

GI: occasional diarrhoea, flatulence, anorexia; Hypomagnesaemia on chronic use (>3 months); Possible vitamin B12 malabsorption on chronic use; Rebound hyperacidity on abrupt discontinuation after long courses; Rare hepatotoxicity (mild ALT elevation); Drug interactions via CYP2C19 inhibition (clopidogrel, warfarin, diazepam).

## Sources

- Plumb's Veterinary Drug Handbook
- Plumbs 9th Ed; AAEP EGUS guidelines 2023
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

---

VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.