Ranitidine
Ranitidine hydrochloride
Also known as: Zantac 75 · Zantac EFFERdose · AH-19065 · ranitidini hydrochloridum · Ranitidinum
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 |
|---|---|---|---|---|---|
| For esophagitis | 1-2 mg/kg | PO | twice daily | — | 🌎 NA |
| For chronic gastritis | 0.5 mg/kg | PO | twice daily | — | 🌎 NA |
| For ulcer disease | 0.5-2 mg/kg | PO, IV or IM | q8-12h | — | 🌎 NA |
| For ulcer disease | 2 mg/kg | PO, IV | q8h | — | 🌎 NA |
| For ulcer disease (also used for esophagitis) | 1-2 mg/kg | PO, IV, SC | q12h | — | 🌎 NA |
| For ulcer disease | 2 mg/kg | PO, IV | q12h | — | 🌎 NA |
| For gastrinoma | 1-2 mg/kg | PO, SC, IV | q8-12h | — | 🌎 NA |
| For gastrinoma | 0.5 mg/kg | PO, IV or SC | twice daily | — | 🌎 NA |
| To treat hypergastrinemia secondary to chronic renal failure | 1-2 mg/kg | PO | twice daily | — | 🌎 NA |
| To treat hyperhistaminemia secondary to mast cell tumors | 2 mg/kg | PO/IV/IM/SC | q12h | — | 🌎 NA |
| As a prokinetic agent to stimulate gastric contractions | 1-2 mg/kg | PO | q12h | — | 🌎 NA |
| All uses (ulcers, gastritis, prokinetic) | 2 mg/kg | slow IV, SC, PO | q8-12h | Typically 1 month for ulcers (2 weeks post-remission) | 🌍 EU |
- To treat hyperhistaminemia secondary to mast cell tumors: Route not explicitly specified in this line of monograph, typically PO/injectable
- All uses (ulcers, gastritis, prokinetic): Absorption is not clinically significantly affected by food intake.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For ulcer disease/esophagitis | 2.5 mg/kg IV q12h or 3.5 mg/kg PO q12h | IV, PO | q12h | — | 🌎 NA |
| For ulcer disease/esophagitis | 1-2 mg/kg | PO, IV, SC | q12h | — | 🌎 NA |
| For ulcer disease/esophagitis | 2 mg/kg | PO, IV | q12h | — | 🌎 NA |
| As a prokinetic agent to stimulate colonic motility | 1-2 mg/kg | PO | q8-12h | — | 🌎 NA |
| As a prokinetic agent to stimulate colonic motility | 1-2 mg/kg | PO | q12h | — | 🌎 NA |
| All uses | 2 mg/kg/day | IV | constant infusion | — | 🌍 EU |
| All uses | 2.5 mg/kg | IV | Not specified | — | 🌍 EU |
- All uses: Not an effective acid suppressant in healthy cats.
- All uses: Not an effective acid suppressant in healthy cats.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| As a prokinetic in rabbits | 0.5 mg/kg | IV | q24h | — | 🌎 NA |
| For suspected gastric ulceration in rabbits | 2-5 mg/kg | PO | twice daily | — | 🌎 NA |
- As a prokinetic in rabbits: Used with cisapride (0.5 mg/kg PO q8h).
Ferrets
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For Helicobacter mustelae | 24 mg/kg | PO | q8-12h | 14 days | 🌎 NA |
- For Helicobacter mustelae: Uses Ranitidine bismuth citrate (must be compounded). Given with clarithromycin (12.5 mg/kg PO q8-12h).
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Foals | 1.5 mg/kg IV q8h or 6.6 mg/kg PO q8h | IV, PO | q8h | — | 🌎 NA |
| Foals | 6.6 mg/kg IV q4h or 0.8-2.2 mg/kg IV four times a day; 5-10 mg/kg PO two to four times a day. | IV, PO | q4h or QID (IV); BID-QID (PO) | — | 🌎 NA |
| Adults | 1.5-2 mg/kg IV or IM q6-8h; 6.6 mg/kg PO q8h | IV, IM, PO | q6-8h (IV/IM); q8h (PO) | — | 🌎 NA |
- Foals: Often used with omeprazole (4 mg/kg PO q24h).
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Ranitidine is a competitive histamine H2-receptor antagonist and gastrointestinal prokinetic agent used widely in veterinary medicine.
Key Clinical Features:
- Acid Suppression: Used for the treatment and prophylaxis of gastric, abomasal, and duodenal ulcers, uremic gastritis, and stress-related or drug-induced erosive gastritis.
- Prokinetic Activity: Uniquely among H2 blockers, ranitidine stimulates GI motility, making it useful for delayed gastric emptying and stimulating colonic activity in cats (e.g., for megacolon).
- Systemic Mastocytosis: Helps manage hypersecretory conditions associated with mast cell tumors (which release massive amounts of histamine).
Clinical Pearl: Ranitidine is 3 to 13 times more potent than cimetidine on a molar basis. Furthermore, it has significantly fewer drug interactions because it does not appreciably inhibit hepatic cytochrome P450 enzymes, making it a safer choice for patients on multiple medications.
Mechanism of action
Ranitidine exerts its effects via two distinct mechanisms:
- Gastric Acid Suppression: It competitively inhibits histamine at the H2 receptors located on the basolateral membrane of gastric parietal cells.
- Histamine blockade → decreased intracellular cAMP → reduced activation of the H+/K+ ATPase (proton pump) → significant reduction in both basal and stimulated gastric acid and pepsin secretion.
- Prokinetic Effect: It reversibly inhibits acetylcholinesterase (AChE) in the gastrointestinal tract.
- AChE inhibition → decreased breakdown of acetylcholine → increased acetylcholine (ACh) at muscarinic receptors → stimulation of GI smooth muscle motility and increased lower esophageal sphincter pressure.
Safety & warnings
Contraindications
- Hypersensitivity to ranitidine
- No specific contraindications available in the monograph
Adverse effects
- Vomiting (associated with rapid IV boluses in small animals)
- Pain at the injection site (IM administration)
- Mental confusion (rare, documented in humans)
- Headache (rare, documented in humans)
- Agranulocytosis (rare)
- Transient cardiac arrhythmias (if given too rapidly IV)
- Cardiac arrhythmias (rare, typically with rapid IV)
- Hypotension (rare, typically with rapid IV)
Precautions
Use cautiously and consider reduced dosages in patients with diminished renal function or hepatic insufficiency, as the drug may accumulate.
Geriatric patients may be more susceptible to adverse effects.
High-dose, chronic IV therapy (longer than 5 days) has caused increased serum ALT levels in humans; monitoring liver enzymes is recommended in these scenarios.
Use with caution in nursing veterinary patients, as ranitidine is excreted in breast milk (milk:plasma ratio of 5:1 to 12:1).
Drug interactions
Ranitidine (dose-dependent) may inhibit acetaminophen metabolism.
High doses may decrease the absorption of ranitidine; administer at least 2 hours apart.
Absorption of ketoconazole may be reduced secondary to increased gastric pH.
Absorption of itraconazole may be reduced secondary to increased gastric pH.
Ranitidine may increase metoprolol half-life and peak serum levels.
Ranitidine may increase nifedipine AUC by 30%.
Delays the absorption but increases the peak serum level of ranitidine; relative bioavailability may be increased by 23%.
Long-term ranitidine use may reduce oral absorption of Vitamin B-12.
May affect absorption; advisable to administer sucralfate 2 hours before H2 blockers
Ranitidine may reduce absorption or effect; stagger oral doses by 2 hours
Ranitidine may reduce absorption or effect; stagger oral doses by 2 hours
Monitoring
- Clinical efficacy (resolution of clinical signs, improved appetite, absence of blood in feces/vomitus)
- Endoscopic examination (if indicated for ulcer healing)
- Serum ALT values (consider monitoring during high-dose, chronic IV therapy)
- Resolution of gastrointestinal clinical signs
- Heart rate and blood pressure (during IV administration)
Pharmacokinetics
Half-life
Absorption
Dogs: Oral bioavailability is ~81%. Horses: Oral bioavailability is ~27% in adults and 38% in foals. Peak levels occur in 100 mins (adults) and 60 mins (foals). Humans: Rapidly absorbed but undergoes extensive first-pass metabolism (net bioavailability ~50%). Food does not appreciably alter absorption.
Distribution
Widely distributed throughout the body. Volume of distribution: 2.6 L/kg (dogs), 1.1 L/kg (adult horses), 1.5 L/kg (foals). Only 10-19% bound to plasma proteins. Distributes into milk at 25-100% of plasma levels.
Metabolism
Metabolized in the liver to inactive metabolites.
Elimination
Excreted in the urine by the kidneys via glomerular filtration and tubular secretion. Clearance in horses is ~10 mL/min/kg (adults) and 13.3 mL/min/kg (foals).
Overdose
Clinical experience with ranitidine overdosage is limited, but the drug has a wide margin of safety.
- Signs of Toxicity: In laboratory animals, massive doses (225 mg/kg/day) have caused muscular tremors, vomiting, and rapid respirations. Single doses of 1 gram/kg in rodents were not fatal.
- Treatment: Handle using standard protocols for oral drug ingestions (e.g., gastric decontamination if recent and appropriate). Treat clinical signs symptomatically and supportively. Hemodialysis and peritoneal dialysis can effectively remove ranitidine from the body.
Available products
Formulations
- Effervescent oral tablets
- Oral solution
- Injection
- Injectable: 25 mg/ml solution
- Oral: 75 mg tablet
- Oral: 150 mg tablet
- Oral: 300 mg tablet
- Oral: 15 mg/ml syrup
Veterinary
- None (No veterinary-labeled products currently available)
Human-labeled
- Ranitidine HCl Oral Tablets: 75 mg, 150 mg & 300 mg (Zantac, Zantac 75, generic)
- Ranitidine HCl Effervescent Oral Tablets: 25 mg & 150 mg (Zantac EFFERdose)
- Ranitidine HCl Solution: 15 mg/mL (Zantac, generic)
- Ranitidine HCl Injection: 1 mg/mL (premixed) & 25 mg/mL (Zantac, generic)
- Ranitidine 75 mg, 150 mg, 300 mg tablets
- Ranitidine 15 mg/ml syrup
- Ranitidine 25 mg/ml injectable solution
Regulatory status
POM (Prescription Only Medicine)
POM (Prescription Only Medicine)
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets in tight, light-resistant containers at room temperature. Store injectable products protected from light at temperatures less than 30°C. A slight darkening of the injectable solution does not affect potency. Injection is stable up to 48 hours when mixed with commonly used IV solutions (including 5% sodium bicarbonate).
Client information
Ranitidine is a medication used to reduce stomach acid and help food move through the digestive tract more effectively.
- Administration: Give this medication exactly as prescribed by your veterinarian. Do not skip doses, as stomach acid levels can rebound and symptoms may return.
- Timing: It can be given with or without food. If your pet is also taking antacids, give them at least 2 hours apart from ranitidine.
- Side Effects: Ranitidine is generally very safe and well-tolerated. Side effects are rare but can include mild stomach upset.
- Storage: Keep tablets in a tightly sealed container at room temperature, away from direct light.
Note: Always consult your veterinarian before giving any new medications or supplements, though ranitidine has fewer drug interactions than older antacids like cimetidine.
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.