Ranitidine

Ranitidine is a histamine H2-receptor antagonist used to reduce gastric acid secretion. Veterinary applications have included selected acid-related upper gastrointestinal disorders. It also has a separate, modest prokinetic action proposed to arise from cholinesterase inhibition. Clinical evidence and the magnitude of each effect vary with species and indication.

Group

Histamine H2-receptor antagonist

Mechanism of Action

Ranitidine blocks histamine H2 receptors on gastric parietal cells, decreasing signaling that activates acid secretion and increasing gastric pH. This reduces acid exposure at damaged gastric or esophageal mucosa. Inhibition of acetylcholinesterase can increase cholinergic activity in the gastrointestinal tract, providing a separate rationale for selected gastric or colonic motility applications.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule
Gastric acid suppression	2 mg/kg	IV, PO	Every 8 h
Esophagitis	1–2 mg/kg	PO	Every 12 h
Chronic gastritis	0.5 mg/kg	PO	Every 12 h
Gastric ulcer disease	0.5–2 mg/kg	PO, IV, IM	Every 8–12 h
Gastric ulcer disease	1–2 mg/kg	PO, IV, SC	Every 12 h
Gastrinoma	1–2 mg/kg	PO, IV, SC	Every 8–12 h
Renal disease-associated hypergastrinemia	1–2 mg/kg	PO	Every 12 h
Gastric prokinetic treatment	1–2 mg/kg	PO	Every 12 h

Cats

Use / stage	Dose	Route	Schedule
Gastric acid suppression	2.5 mg/kg	IV	Every 12 h
Gastric acid suppression	3.5 mg/kg	PO	Every 12 h
Gastric acid suppression	1–2 mg/kg	PO, IV, SC	Every 12 h
Colonic prokinetic treatment	1–2 mg/kg	PO	Every 8–12 h

Horses

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	2.2–6.6 mg/kg	PO	Every 6–8 h	Higher reported dose gives greater acid suppression.
Gastric acid suppression	2 mg/kg	IV	Every 6–8 h
Foal acid suppression	1.5 mg/kg	IV	Every 8 h
Foal acid suppression	6.6 mg/kg	PO	Every 8 h
Acid suppression	1.5–2 mg/kg	IV, IM	Every 6–8 h

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression in milk-fed calves	50 mg/kg	PO	Every 8 h
Gastric acid suppression in adults	6.6 mg/kg	IM		Reported experience indicates only about 1 hour of effect.

Rabbits

Use / stage	Dose	Route	Schedule	Instructions
Gastric ulceration	2–5 mg/kg	PO	Every 12 h
Prokinetic adjunct	0.5 mg/kg	IV	Every 24 h	Reported with cisapride 0.5 mg/kg orally every 8 hours.

Indications

Acid suppression in selected veterinary patients with gastroduodenal ulceration or acid-related erosive disease.
Adjunctive reduction of gastric acid exposure in reflux esophagitis.
Management of selected gastric hypersecretory states, including gastrinoma-associated hypersecretion.
Empirical adjunctive treatment of selected delayed gastric emptying or feline colonic hypomotility, with limited clinical evidence.

Contraindications

Reduced renal clearance can increase exposure.

Interactions

Reduces absorption of acid-dependent drugs including azole antifungals and iron.

Adverse effects

CNS effects are possible at high exposure; product impurity quality matters.

Toxicity

High exposure may cause tremor, vomiting and rapid respiration; manage clinical effects supportively and account for renal elimination.

Preparations

Preparation	Form	Strength	Route
Ranitidine reformulated tablet 150 mg	Tablet	150 mg / tablet	PO
Ranitidine reformulated tablet 300 mg	Tablet	300 mg / tablet	PO

Monitoring and Administration

Monitor acid-related disease response and renal function when relevant. Historical stock and newly reformulated products should not be treated as equivalent in quality assurance.

Earlier guidance describes historical NDMA-related withdrawal. Reformulated tablets have subsequently been approved; availability and quality remain product-specific.

Ranitidine-bismuth-citrate 24 mg/kg orally every 8-12 hours plus clarithromycin 12.5 mg/kg for 14 days in ferrets is a different combination ingredient and is not a ranitidine-only dose. The unusually high foal 6.6 mg/kg IV every 4 hours differs materially from other IV regimens and needs independent route/unit clarification.