Famotidine

Famotidine is a histamine H2-receptor antagonist used for gastric acid suppression. Veterinary applications involve selected acid-related upper gastrointestinal disorders in dogs, cats and other species. Its effect can be useful for short-term reduction of acid exposure, although the magnitude and persistence of suppression vary with the patient, route and duration of administration.

Group

H2-receptor antagonist

Mechanism of Action

Famotidine blocks histamine H2 receptors on gastric parietal cells. Reduced receptor signaling lowers cyclic-AMP-mediated activation of the acid-secretory pathway, decreasing basal and stimulated gastric acid output. A higher gastric pH reduces acid exposure of damaged gastric, duodenal or esophageal mucosa. The principal effect is suppression of acid secretion rather than direct treatment of the emetic reflex.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Acid suppression	0.5 mg/kg	PO, IV, IM, SC	Every 12 h
Acid suppression	1 mg/kg	PO	Every 12 h	Higher oral alternative; therapeutic pH targets are not consistently achieved.
Acid suppression	40 mg/animal	PO	Every 12 h	Empirical fixed alternative.
Acid suppression infusion — Loading	1 mg/kg	IV
Acid suppression infusion — Maintenance	0.3333333333 mg/kg/hour	IV	Continuous	Equivalent to 8 mg/kg per 24 hours.

Cat

Use / stage	Dose	Route	Schedule	Instructions
Acid suppression	0.2 mg/kg	PO, IV, IM, SC	Every 24 h
Acid suppression	0.25 mg/kg	PO, IV, IM, SC	Every 12 h	Alternative higher-frequency regimen; IV slowly over 5 minutes.

Horse

Use / stage	Dose	Route	Schedule
Acid suppression	1–2 mg/kg	PO	Every 6–8 h
Acid suppression	0.2–0.4 mg/kg	IV	Every 6 h
Gastric ulcer adjunct	0.23 mg/kg	IV	Every 8 h
Gastric ulcer adjunct	0.35 mg/kg	IV	Every 12 h
Gastric ulcer adjunct	1.88 mg/kg	PO	Every 8 h
Gastric ulcer adjunct	2.8 mg/kg	PO	Every 12 h

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Acid suppression	0.4 mg/kg	IV	Every 6 h

Ferret

Use / stage	Dose	Route	Schedule	Instructions
Stress-associated ulceration	0.25–0.5 mg/kg	PO, IV	Every 24 h

Rabbit

Use / stage	Dose	Route	Schedule	Instructions
Stress-ulcer prevention	1 mg/kg	IV	Every 24 h	After stabilization of the critically ill rabbit.

Indications

Short-term gastric acid suppression in selected dogs and cats with suspected or documented acid-related gastroduodenal injury.
Adjunctive reduction of acid exposure in reflux esophagitis.
Management of selected gastric hypersecretory states, including gastrinoma or histamine-associated hypersecretion in mast-cell disease.

Contraindications

Adjust for impaired renal clearance.

Interactions

Reduced acidity can impair absorption of azoles and iron.

Adverse effects

Potential CNS effects at excessive exposure
Rapid injection reactions, especially with benzyl-alcohol formulations in cats

Preparations

Preparation	Form	Strength	Route
Famotidine 20 mg	Tablet	20 mg / tablet	PO
Famotidine 40 mg	Tablet	40 mg / tablet	PO
Famotidine suspension 8 mg/mL	Oral Liquid	8 mg / mL	PO
Famotidine injection 10 mg/mL	Injection	10 mg / mL	IV, IM, SC

Monitoring and Administration

Oral acid suppression may diminish with repeated dosing; PPIs generally provide more reliable suppression. It is not an established antiemetic.

Administer feline IV doses slowly, around 5 minutes. Monitor response and renal status.

Source-described saline dilutions are stable for 48 hours at room temperature; compounded oral stability depends on vehicle.