Famotidine
3-[({2-[(diaminomethylidene)amino]-1,3-thiazol-4-yl}methyl)sulfanyl]-N'-sulfamoylpropanimidamide
Also known as: Pepcid AC · Pepcid RPD · famotidinum · L-643341 · MK-208 · YM-11170 · Famotidina
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 |
|---|---|---|---|---|---|
| To reduce gastric acid production | 0.1-0.2 mg/kg | PO, SC, IM, IV | q12h | — | 🌎 NA |
| To reduce gastric acid production | 0.5 mg/kg | PO, SC, IM, IV | q12-24h | — | 🌎 NA |
| For esophagitis | 0.5-1 mg/kg | PO | q12h | — | 🌎 NA |
| For acute reflex esophagitis | 0.55-1.1 mg/kg | PO | q24h (or q12h if severe) | 2-3 weeks | 🌎 NA |
| Adjunctive treatment (prevent/treat gastric ulcers) of mast cell tumors | 0.5 mg/kg | Not specified | q24h | — | 🌎 NA |
| Adjunctive treatment of GI effects associated with chronic kidney disease | 0.5 mg/kg | PO | q24h | — | 🌎 NA |
| All uses (ulcers, gastritis, oesophagitis, hypersecretory conditions) | 0.5-1.0 mg/kg | PO | q12-24h | — | 🌍 EU |
- Adjunctive treatment of GI effects associated with chronic kidney disease: Effective evidence grade: 3
- All uses (ulcers, gastritis, oesophagitis, hypersecretory conditions): Effect on gastric pH diminishes with time when given daily.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| To reduce gastric acid production | 0.2 mg/kg | PO, SC, IM, IV | q24h | — | 🌎 NA |
| To reduce gastric acid production | 0.5 mg/kg | PO, SC, IM, IV | q12-24h | — | 🌎 NA |
| For esophagitis | 0.5 mg/kg | PO | q12h | — | 🌎 NA |
| For acute reflex esophagitis | 0.55-1.1 mg/kg | PO | q24h (or q12h if severe) | 2-3 weeks | 🌎 NA |
| Adjunctive treatment of GI effects associated with chronic progressive renal disease | 1 mg/kg | PO | q24h | — | 🌎 NA |
| Adjunctive treatment of GI effects associated with chronic progressive renal disease | 0.5-1 mg/kg | PO | q12-24h | — | 🌎 NA |
| All uses (ulcers, gastritis, oesophagitis, hypersecretory conditions) | 0.5-1.0 mg/kg | PO | q12-24h | — | 🌍 EU |
- To reduce gastric acid production: See warning about IV use in cats
- All uses (ulcers, gastritis, oesophagitis, hypersecretory conditions): Effect on gastric pH diminishes with time when given daily.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Rabbits: For stress induced ulcer prevention once critically ill animal has stabilized | 1 mg/kg | IV | q24h | — | 🌎 NA |
Ferrets
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For stress induced ulcers | 0.25-0.5 mg/kg | PO, IV | q24h | — | 🌎 NA |
| In combination with antibiotics for Helicobacter treatment | 0.25-0.5 mg/kg | PO, IV | q24h | — | 🌎 NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| As an adjunct in ulcer treatment | 0.23 mg/kg or 0.35 mg/kg | IV | q8h (for 0.23 mg/kg) or q12h (for 0.35 mg/kg) | — | 🌎 NA |
| As an adjunct in ulcer treatment | 1.88 mg/kg or 2.8 mg/kg | PO | q8h (for 1.88 mg/kg) or q12h (for 2.8 mg/kg) | — | 🌎 NA |
- As an adjunct in ulcer treatment: ARCI UCGFS Class 5 Drug
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Famotidine is a potent, long-acting histamine H2-receptor antagonist used widely in veterinary medicine to suppress gastric acid production and treat or prevent gastric/duodenal ulcers, gastritis, and esophagitis.
Compared to cimetidine, famotidine is significantly more potent, requires less frequent dosing, and crucially, does not inhibit the hepatic cytochrome P450 enzyme system, making it free of many common drug interactions.
Clinical Pearl: While effective for mild acid suppression or routine prophylaxis, proton pump inhibitors (PPIs) like omeprazole are generally considered superior for treating active ulcers, preventing exercise-induced gastritis, or managing severe esophagitis. Furthermore, famotidine is prone to pharmacological tolerance (tachyphylaxis) within 3 to 14 days of continuous use in dogs and cats, which diminishes its acid-suppressing efficacy over time.
Mechanism of action
Famotidine acts as a competitive, reversible antagonist at the H2 receptors located on the basolateral membrane of gastric parietal cells.
By blocking histamine binding, it prevents the activation of adenylate cyclase → decreases intracellular cAMP levels → reduces the activation of the H+/K+-ATPase proton pump. This effectively blunts both basal gastric acid secretion and secretion stimulated by food, pentagastrin, or insulin. By decreasing the total volume of gastric juice produced, H2-blockers also indirectly decrease the amount of pepsin secreted. It does not alter gastric emptying time, biliary secretion, or lower esophageal sphincter pressure.
Safety & warnings
Contraindications
- Known hypersensitivity to H2 blockers
- Known hypersensitivity to famotidine or other H2 receptor antagonists
Adverse effects
- Bradycardia (if infused too rapidly IV)
- GI effects (anorexia, vomiting, diarrhea)
- Headache
- Dry mouth or skin
- Intravascular hemolysis (rare, anecdotally reported in cats given IV)
- Transient increase in serum gastrin (returns to baseline by 14 days)
- Generally has a very good safety profile with fewer side effects than cimetidine
Precautions
Use cautiously in geriatric patients and those with significantly impaired hepatic or renal function; consider dosage reduction in patients with significant renal dysfunction. Famotidine may have negative inotropic effects and some cardioarrhythmogenic properties; use with caution in patients with cardiac disease. When administering IV to cats, infuse slowly (over 5 minutes) to minimize the rare risk of intravascular hemolysis.
Drug interactions
Famotidine raises gastric pH, which may decrease the absorption of these agents. Administer the azole one hour prior to famotidine.
Famotidine may decrease the absorption of these cephalosporins. Taking with food may alleviate this effect.
Famotidine may decrease the absorption of oral iron. Administer iron at least one hour prior to famotidine.
Monitoring
- Clinical efficacy (decrease in symptomatology, endoscopic examination, resolution of blood in feces)
- Adverse effects
- Clinical signs of GI ulceration or bleeding (vomiting, melena, anorexia)
- Gastric pH (if clinically indicated and feasible)
Pharmacokinetics
Half-life
Absorption
Incompletely absorbed after oral administration with minimal first-pass metabolism. Systemic bioavailability is ~40-50% in humans. Bioavailability is low in horses (13%).
Distribution
Concentrates in the liver, pancreas, kidney, and submandibular gland (in rats). Only ~15-20% is bound to plasma proteins. Does not cross the blood-brain barrier or placenta in rats. Distributed into milk. Volume of distribution in horses is 4.28 L/kg.
Metabolism
Primarily metabolized in the liver.
Elimination
Excreted in the urine. After oral dosing, ~1/3 is excreted unchanged; after IV dosing, ~2/3 is excreted unchanged.
Overdose
Famotidine has a wide margin of safety. The minimum acute lethal dose in dogs is reported to be >2 grams/kg for oral doses and approximately 300 mg/kg for intravenous doses.
IV doses in dogs ranging from 5-200 mg/kg caused vomiting, restlessness, mucous membrane pallor, and redness of the mouth and ears. Higher doses caused hypotension, tachycardia, and collapse.
Most overdoses require only monitoring. In massive oral overdoses, gut-emptying protocols should be considered and supportive therapy initiated when warranted.
Available products
Formulations
- Oral tablets (plain, film-coated, chewable, orally disintegrating)
- Powder for oral suspension
- Injection
- 20 mg tablets
- 40 mg tablets
Human-labeled
- Famotidine Oral Tablets (plain, film-coated, chewable & orally disintegrating) & Gelcaps: 10 mg, 20 mg, & 40 mg (Pepcid®, Pepcid AC®, generic)
- Famotidine Powder for Oral Suspension: 8 mg/mL when reconstituted (Pepcid®)
- Famotidine Injection: 10 mg/mL in vials; 20 mg/50 mL premixed containers (generic)
- 20 mg tablets
- 40 mg tablets
Regulatory status
Human authorized product used off-label under the cascade. Cimetidine is the only H2 antagonist with veterinary authorization.
Human authorized product used off-label under the cascade (POM).
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Tablets should be stored in well-closed, light-resistant containers at room temperature. Powder for oral suspension should be stored <40°C; after reconstitution, it is stable for 30 days when stored <30°C (do not freeze). Injection should be stored in the refrigerator (2-8°C).
Client information
- Administration: Give this medication exactly as prescribed by your veterinarian. To maximize its acid-blocking effect, it is often best given on an empty stomach, about 30-60 minutes before a meal.
- Consistency: Do not skip doses. Clinical signs of acid reflux or ulcers may reoccur if dosages are missed.
- Liquid Formulations: If using a compounded liquid suspension, shake well before each use and store it in the refrigerator. Discard any unused portion after 30 days.
- Interactions: Inform your veterinarian of any other medications or supplements your pet is taking. If your pet takes oral iron supplements or certain antifungal medications, they should be given at least one hour apart from famotidine.
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.