Ranitidine Hydrochloride

H2 receptor antagonist Antiulcer agent / Gastric acid reducer

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 2 mg/kg q12h (every 12 hours) Duration: 2-4 weeks or as needed
Notes: For severe cases, may be given q8h. Administer on an empty stomach for best absorption.
Dog IV/IM 0.5-1 mg/kg q8-12h Duration: Until oral therapy is tolerated
Notes: Slow IV injection over 2 minutes or as an infusion.
Cat PO 2.5 mg/kg q12h Duration: 2-4 weeks or as needed
Notes: May be given q8h for severe esophagitis.
Cat IV/IM 1-2 mg/kg q12h Duration: Until oral therapy is tolerated
Notes: Slow IV injection.
Horse PO 6.6 mg/kg q8h Duration: For EGUS: 2-4 weeks; may be used long-term for prevention
Notes: Administer via nasogastric tube or oral paste. For prevention, 2.2 mg/kg q8h may be used.
Horse IV 1.5 mg/kg q8h Duration: For acute cases or when oral not possible
Notes: Slow IV injection.
Cattle PO 2-4 mg/kg q12h Duration: As needed
Notes: Limited data; use with caution.
Cattle IV 1 mg/kg q12h Duration: As needed
Notes: Slow IV injection.
Small Ruminants (sheep/goats) PO 2-4 mg/kg q12h Duration: As needed
Notes: Limited data; use with caution.
Rabbit PO 2-5 mg/kg q12h Duration: As needed
Notes: May be used in gastric stasis as adjunctive therapy.
Bird/Poultry PO 2-5 mg/kg q12h Duration: As needed
Notes: Limited data; use with caution.
Exotic (ferrets) PO 2.5 mg/kg q12h Duration: As needed
Notes: Limited data.

Clinical Indications & Species Uses

General Indications
  • Treatment of gastric and duodenal ulcers
  • Management of gastritis and esophagitis
  • Reduction of gastric acid secretion in various conditions
Dog (Canine)
  • Gastric and duodenal ulcers
  • Gastritis
  • Gastroesophageal reflux disease (GERD)
  • Esophagitis
  • Mast cell tumor (as adjunct to reduce histamine-induced acid secretion)
  • Stress-related gastric ulceration
  • Prevention of gastric ulcers in patients on NSAIDs or corticosteroids
Cat (Feline)
  • Gastric and duodenal ulcers
  • Gastritis
  • Gastroesophageal reflux disease (GERD)
  • Esophagitis
  • Chronic kidney disease (to reduce gastric acid and uremic gastritis)
  • Inflammatory bowel disease (adjunctive therapy)
Horse (Equine)
  • Gastric ulceration (equine gastric ulcer syndrome, EGUS)
  • Prevention of gastric ulcers in performance horses
  • Esophagitis
  • Gastritis
Cattle (Bovine)
  • Abomasal ulcers
  • Indigestion
  • Gastrointestinal stasis (adjunctive)
  • Prevention of abomasal ulcers in calves
Small Ruminants (Sheep / Goat)
  • Abomasal ulcers
  • Gastritis
  • Gastroesophageal reflux
Rabbit & Small Mammals
  • Gastric ulcers
  • Gastric stasis (adjunctive)
  • Gastrointestinal hypersecretion
Avian & Poultry
  • Gastric ulcers
  • Gastrointestinal reflux
  • Stress-related gastric lesions
Exotic & Other Species
  • Gastric ulcers in ferrets
  • Gastroesophageal reflux in reptiles (limited data)

Pharmacology & Mechanism of Action

Drug Class: H2 receptor antagonist | Pharmacological Group: Antiulcer agent / Gastric acid reducer

Mechanism of Action: Ranitidine is a competitive, reversible inhibitor of histamine at the H2 receptors on gastric parietal cells. By blocking histamine stimulation, it reduces basal and stimulated gastric acid secretion, including secretion stimulated by food, pentagastrin, and insulin. It also reduces pepsin secretion and gastric juice volume. Unlike H1 antagonists, it has no effect on H1 receptors. Ranitidine does not alter gastric emptying or lower esophageal sphincter pressure significantly.

Pharmacodynamics: Ranitidine inhibits gastric acid secretion for several hours after a single dose. It reduces both the volume and acidity of gastric juice. It is less potent than proton pump inhibitors but has a faster onset of action. It also has a cytoprotective effect by increasing gastric mucosal blood flow and mucus production. In veterinary patients, it is used to manage conditions associated with gastric hyperacidity and ulceration.

⚡ Pharmacokinetics Summary

Absorption: Ranitidine is well absorbed after oral administration in most species, but bioavailability varies: approximately 50% in dogs, 80% in cats, and 40% in horses. Food may decrease the rate of absorption. Peak plasma concentrations occur within 1-2 hours after oral dosing.
Distribution: Ranitidine is widely distributed throughout the body, including into the cerebrospinal fluid and placenta. It crosses the blood-brain barrier to a small extent. It is not highly protein-bound (approximately 15% in humans; similar in animals).
Metabolism: Ranitidine undergoes minimal hepatic metabolism. It is primarily metabolized to N-oxide, S-oxide, and desmethyl ranitidine, which are pharmacologically inactive. The liver's first-pass effect reduces oral bioavailability.
Excretion: Ranitidine is primarily excreted unchanged in the urine via tubular secretion. Renal clearance is high. In animals with renal impairment, dose adjustments may be necessary. A small amount is excreted in feces.
Half-Life: Dogs: approximately 2-3 hours; Cats: approximately 2.5 hours; Horses: approximately 1.5-2 hours; Humans: 2-3 hours.
Bioavailability: Oral: Dogs ~50%, Cats ~80%, Horses ~40%. Injectable is 100% bioavailable.
Protein Binding: Approximately 15% in most species.

Available Formulations & Strengths

Oral Tablet 75 mg, 150 mg, 300 mg (PO)
Oral Syrup 15 mg/mL (PO)
Injectable Solution 25 mg/mL (IV/IM)

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to ranitidine or other H2 antagonists
  • Severe renal impairment (dose adjustment required; may be contraindicated if no alternative)
  • Hepatic dysfunction with encephalopathy (use with caution)
  • Porphyria (may precipitate acute attacks)
Warnings & Clinical Precautions:
  • Use with caution in patients with renal or hepatic impairment; dose adjustment may be necessary.
  • May mask symptoms of gastric malignancy; rule out neoplasia in chronic cases.
  • Use with caution in geriatric patients.
  • In horses, oral administration may be less effective in severe EGUS; consider omeprazole for treatment.
  • Rapid IV injection may cause bradycardia or hypotension; administer slowly.
  • Long-term use may lead to vitamin B12 deficiency due to reduced acid secretion.
  • In food animals, observe withdrawal times.

Adverse Effects & Reactions

Common:

  • Gastrointestinal disturbances (diarrhea, constipation, nausea)
  • Anorexia
  • Headache (in humans; not observed in animals)

Serious / Severe:

  • Arrhythmias (with rapid IV administration)
  • Hepatotoxicity (rare)
  • Blood dyscrasias (thrombocytopenia, leukopenia)
  • Anaphylaxis (rare)
  • Central nervous system signs (confusion, agitation) in renal/hepatic impairment

Rare:

  • Gynecomastia
  • Impotence
  • Interstitial nephritis
  • Pancreatitis
  • Alopecia

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Ketoconazole Reduced absorption of ketoconazole due to increased gastric pH. Moderate
Itraconazole Reduced absorption of itraconazole due to increased gastric pH. Moderate
Antacids (aluminum/magnesium hydroxide) May reduce absorption of ranitidine; separate administration by at least 1 hour. Mild
Sucralfate May reduce absorption of ranitidine; separate administration by at least 2 hours. Mild
Warfarin May increase anticoagulant effect; monitor prothrombin time. Moderate
Procainamide May reduce renal clearance of procainamide; monitor for toxicity. Moderate
Triazolam May increase absorption of triazolam; monitor for increased sedation. Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Vomiting
  • Diarrhea
  • Ataxia
  • Tremors
  • Seizures (in severe cases)
  • Respiratory depression
  • Bradycardia or tachycardia

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Induce emesis if recent ingestion and patient is conscious. Administer activated charcoal to reduce absorption. Provide IV fluids for dehydration. Monitor vital signs and ECG. In severe cases, administer anticonvulsants (e.g., diazepam) for seizures and atropine for bradycardia. There is no specific antidote; ranitidine is dialyzable, but hemodialysis is rarely needed.

Food Animal Withdrawal Times

🥩 Meat: 0 days🥛 Milk: 0 days🥚 Eggs: 0 days

Ranitidine is not approved for food animals in many countries. Withdrawal times may vary by jurisdiction; consult local regulations. In the US, no withdrawal period is established for extra-label use in food animals; a conservative withdrawal time of at least 7 days for meat and 72 hours for milk is often recommended.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F); excursions permitted between 15-30°C (59-86°F).

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep in tightly closed container. Injectable solution should be stored at room temperature and protected from freezing.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use. Some compounded formulations may be available.

Extra-Label (Off-Label) Use: In the US, ranitidine is not FDA-approved for veterinary use in most species; use is extra-label. Under AMDUCA, extra-label use is permitted in animals under a valid veterinarian-client-patient relationship, provided that no approved animal drug is available. For food animals, a withdrawal time must be established by the veterinarian.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Ranitidine is a histamine H2 receptor antagonist used to reduce gastric acid secretion in various animal species. It is less potent than proton pump inhibitors (e.g., omeprazole) but may be preferred in certain situations due to its lower cost and availability. In dogs and cats, it is commonly used for gastritis, ulcers, and reflux. In horses, it is used for EGUS, but omeprazole is often preferred for treatment; ranitidine may be used for prevention. Dosing frequency is typically q8-12h due to its relatively short half-life. Oral bioavailability varies by species; cats have higher bioavailability than dogs. It is generally well tolerated, but adverse effects can occur. In food animals, extra-label use requires careful attention to withdrawal times. Always consider underlying causes of ulceration (e.g., NSAIDs, stress, mast cell tumors) and address them appropriately. For severe or refractory cases, consider proton pump inhibitors. Monitor renal and hepatic function in long-term therapy. Due to potential drug interactions, review the patient's medication list.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)