Omeprazole: veterinary dose and monograph

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

• 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

• 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

• 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

• 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

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

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

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

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
• Mineral Oil (Liquid Paraffin)
• Mirtazapine
• Misoprostol
• Pantoprazole
• Ranitidine
• S-Adenosylmethionine (SAMe)
• Silymarin (Milk Thistle / Silybin)

Frequently asked questions