Drug Monograph
Full clinical overview, indications, dosage references & safety notes.
Drug class: H2-receptor antagonist (with prokinetic activity)
Main indication: Gastric acid suppression – ulceration, gastritis and esophagitis
Available forms4 forms · 7 strengths documentedShow all ↓
Oral · solid
Tablet 75 mg Zantac® · Ranicalm® · genericsTablet 150 mgTablet 300 mgCapsule 150 mg genericCapsule 300 mg generic
Oral · liquid
Oral solution / syrup 15 mg/mL generic
Injection
Injectable solution 25 mg/mL Zantac® and generics
Availability
Availability varies by country; reformulated ranitidine tablets returned to the US market in 2025
Overview
Ranitidine (Zantac®) is an H2-receptor antagonist with additional prokinetic activity. It has been used in dogs and cats to reduce gastric acid production and to manage a variety of upper gastrointestinal disorders.
In veterinary medicine, ranitidine has been used for the treatment and prevention of esophagitis, gastritis, gastrointestinal ulceration, and gastroesophageal reflux. Its prokinetic effects may also support gastrointestinal motility, including stimulation of colonic activity in cats.
Mechanism of Action (MOA): Ranitidine competitively inhibits histamine at H2 receptors on gastric parietal cells, reducing gastric acid secretion under both basal and stimulated conditions. It may also enhance gastrointestinal motility by inhibiting acetylcholinesterase, thereby increasing acetylcholine activity at muscarinic receptors.
Indications
Ranitidine is used in dogs and cats for the management of acid-related gastrointestinal disorders and for its prokinetic effects.
- Esophagitis and gastroesophageal reflux: Treatment and prevention of esophagitis and reflux-associated conditions.
- Gastritis and gastrointestinal ulceration: Management of gastritis and gastric or duodenal ulcer disease.
- Hypersecretory conditions: Management of excessive gastric acid secretion associated with gastrinomas, systemic mastocytosis or short bowel syndrome.
- Prokinetic therapy: Used to enhance gastrointestinal motility, including stimulation of colonic motility in cats, although recent studies question the prokinetic activity of ranitidine in dogs.
- Helicobacter protocols: Adjunctive acid suppression within multidrug protocols for Helicobacter-associated gastritis.
Dosage (Reference)
Dog
Ranitidine has been used for esophagitis, gastritis, gastrointestinal ulceration, and as a gastric prokinetic agent. Published dosing recommendations vary, and evidence supporting efficacy in dogs remains limited.
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Esophagitis, gastritis, ulcer disease, or gastric prokinetic therapy | PO / SC / IM / Slow IV | 1–2 mg/kg | q8–12h | For ulceration, continue treatment for 2 weeks after clinical signs resolve, which is typically a one-month course. |
| Acid suppression study | IV | 2 mg/kg | q12h | Did not significantly increase gastric pH compared with saline in one study. |
Important dosing notes (dogs):
• Administer IV doses slowly; the maximum IV administration rate is 25 mg/minute. The human manufacturer recommends diluting to 2.5 mg/mL in 5% dextrose or 0.9% sodium chloride; the significance in animals is not known, but the precaution may be considered.
• One source suggested that commonly recommended doses of 0.5–2 mg/kg every 8–12 hours may be too low to produce a meaningful effect.
• Clinical studies evaluating the effects of ranitidine on gastric disorders in dogs are limited.
• Famotidine produced a greater and longer-lasting increase in intragastric pH than ranitidine in dogs; for gastroduodenal ulceration and reflux esophagitis, consensus guidance finds no benefit in once-daily H2-blocker dosing.
• Administer IV doses slowly; the maximum IV administration rate is 25 mg/minute. The human manufacturer recommends diluting to 2.5 mg/mL in 5% dextrose or 0.9% sodium chloride; the significance in animals is not known, but the precaution may be considered.
• One source suggested that commonly recommended doses of 0.5–2 mg/kg every 8–12 hours may be too low to produce a meaningful effect.
• Clinical studies evaluating the effects of ranitidine on gastric disorders in dogs are limited.
• Famotidine produced a greater and longer-lasting increase in intragastric pH than ranitidine in dogs; for gastroduodenal ulceration and reflux esophagitis, consensus guidance finds no benefit in once-daily H2-blocker dosing.
Cat
Ranitidine has been used for esophagitis, ulcer disease, and as a prokinetic agent to stimulate colonic motility.
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Esophagitis, ulcer disease, or colonic prokinetic therapy | Slow IV | 2.5 mg/kg | q12h | Based on pharmacokinetic data. |
| Esophagitis, ulcer disease, or colonic prokinetic therapy | PO | 3.5 mg/kg | q12h | Based on pharmacokinetic data. |
| H. heilmannii eradication protocol (cats) | PO | 20 mg/cat | q12h | Reported as part of a 4-day multidrug H. heilmannii eradication protocol in cats, with clarithromycin, metronidazole and bismuth subsalicylate. |
| Megacolon (colonic prokinetic) | PO | 1–3 mg/kg | q12h | Given if cisapride is unavailable. |
| Helicobacter-associated gastritis (antisecretory component) | PO | 1–2 mg/kg | q12h | Given with two antibiotics; treat for 2–3 weeks. |
Important dosing notes (cats):
• Ranitidine was not an effective acid suppressant in healthy cats, and a consensus review found no difference from placebo at comparable oral doses.
• One study found that 1.4–2.3 mg/kg PO every 12 hours did not significantly suppress gastric acid secretion.
• Administer IV doses slowly when using injectable ranitidine.
• A feline constant-rate infusion of 2 mg/kg/day is also listed.
• Ranitidine was not an effective acid suppressant in healthy cats, and a consensus review found no difference from placebo at comparable oral doses.
• One study found that 1.4–2.3 mg/kg PO every 12 hours did not significantly suppress gastric acid secretion.
• Administer IV doses slowly when using injectable ranitidine.
• A feline constant-rate infusion of 2 mg/kg/day is also listed.
Warnings & Precautions
Ranitidine is generally well tolerated, but dose adjustment, monitoring, and careful patient selection may be necessary in certain situations.
- Hypersensitivity: Contraindicated in patients with known hypersensitivity to ranitidine.
- Renal insufficiency: Use cautiously and consider dose reduction in patients with diminished renal function.
- Hepatic impairment: Use with caution in patients with impaired hepatic function.
- Liver enzyme monitoring: High-dose therapy administered for longer than 5 days has been associated with increased serum ALT levels in humans. Monitoring of serum ALT may be considered during high-dose chronic therapy.
- Geriatric patients: Use cautiously in older patients.
- IV administration: Consider dilution and slow administration when giving ranitidine intravenously.
- Market withdrawal and NDMA: Ranitidine products were withdrawn from the United States market and suspended across the European Union in 2020 after N-nitrosodimethylamine, a probable human carcinogen, was detected in ranitidine products at levels that rise with storage time and temperature, with evidence that it may form from degradation of ranitidine itself.
- Pregnancy and lactation: Laboratory-animal studies revealed no evidence of fetal toxicity, and ranitidine is excreted into human breast milk at milk:plasma ratios of 5:1 to 12:1, so use with caution in nursing patients; avoid gastric prokinetic therapy in pregnant animals.
- Name confusion: Ranitidine is easily confused with rimantadine and amantadine, and the brand name Zantac with Zyrtec and Zofran; confirm the drug name when prescribing or dispensing.
- Gastric outflow obstruction: When used for its gastric prokinetic effect, avoid ranitidine in patients with gastric outflow obstruction.
Drug Interactions
Ranitidine has less effect on hepatic drug metabolism than cimetidine, but several clinically relevant interactions may still occur; one source advises against concurrent theophylline, phenytoin or warfarin, and another reports interference with phenobarbital metabolism with a risk of toxic levels.
- Acetaminophen: Ranitidine may inhibit acetaminophen metabolism in a dose-dependent manner.
- Antacids (e.g., calcium carbonate, magnesium/aluminum combinations): May decrease the oral absorption of ranitidine. Administer the drugs at least 2 hours apart.
- Azole antifungals (e.g., ketoconazole, itraconazole, fluconazole): Increased gastric pH may reduce absorption of these agents. Administer the azole antifungal at least 1 hour before ranitidine.
- Cefpodoxime and cefuroxime: Ranitidine may decrease the absorption of these cephalosporins. Administration with food may reduce this effect.
- Oral iron salts: Ranitidine may decrease iron absorption. Administer iron at least 1 hour before ranitidine.
- Metoprolol: Ranitidine may increase metoprolol half-life and peak plasma concentrations.
- Sucralfate: Best given about 2 hours before an H2 blocker, although the separation is advisable rather than essential.
- Digoxin and metoclopramide: Stagger oral ranitidine and digoxin or metoclopramide by about 2 hours, since absorption or effect may otherwise be reduced.
- Probenecid: May reduce the renal excretion of ranitidine.
- Procainamide: Concurrent use may increase serum procainamide concentrations.
- Propantheline: Delays ranitidine absorption but raises its peak serum level, increasing relative bioavailability by about 23%.
- Vitamin B12: Long-term ranitidine use may reduce oral absorption of vitamin B12.
Side Effects & Overdose
Side Effects
Adverse effects are uncommon at clinical doses, but gastrointestinal, cardiovascular, and hematologic effects have been reported.
- Vomiting: May occur following IV bolus administration in small animals.
- Injection site pain: Pain may occur after IM administration.
- Cardiac arrhythmias: Rapid IV administration may cause transient cardiac arrhythmias.
- Hypotension: Transient hypotension has been reported in cats following IV administration, and hypotension has also been reported after rapid intravenous injection.
- Agranulocytosis: Rarely reported.
- Central nervous system effects: Mental confusion and headache are reported in people, and central nervous system signs may occur at high doses; the relevance to animals is unknown.
- Reduced renal clearance: Adverse effects are otherwise usually seen only with decreased renal clearance.
Overdose
Clinical experience with ranitidine overdose is limited.
- Clinical signs: Very high doses have been associated with muscular tremors, vomiting, and rapid respiration in laboratory animals at 225 mg/kg/day, while single oral doses of 1 g/kg in rodents did not cause death.
- Management: Treatment should follow standard protocols for oral drug overdoses, with symptomatic and supportive care as needed.
- Drug removal: Hemodialysis and peritoneal dialysis may remove ranitidine from the body.
- Poison control: For a known or suspected overdose, consultation with a 24-hour poison control center that specializes in veterinary patients is strongly encouraged.
Key Notes
Practical clinical points for the use of ranitidine in dogs and cats:
- Dual activity: Ranitidine acts as an H2-receptor antagonist and has been described as having prokinetic activity, although that activity is considered weak and has recently been questioned in dogs.
- Gastric motility: May enhance gastric emptying, particularly when delayed gastric emptying is associated with gastric ulcer disease.
- Lower esophageal sphincter tone: May increase lower esophageal sphincter pressure, which may be beneficial in reflux-associated conditions.
- Acid suppression consistency: Reduced efficacy during repeated administration has been reported with H2 blockers; one source reports that this was not seen with ranitidine, while current consensus guidance holds that continuous H2-blocker administration does produce tolerance.
- Comparative efficacy: Proton pump inhibitors such as omeprazole are preferred for ulcer healing and reflux esophagitis because they suppress acid more consistently, and current reviews conclude that ranitidine does not achieve adequate acid suppression in dogs or cats.
- Pharmacokinetics: In dogs the oral bioavailability is about 81%, the serum half-life about 2.2 hours and the volume of distribution 2.6 L/kg; acid suppression is reported to last up to about 8 hours, against 3 to 5 hours for cimetidine, which is why ranitidine can be given less often.
- Potency versus cimetidine: Ranitidine is more potent than cimetidine; sources put it at 3 to 13 times on a molar basis, while another gives 4 to 10 times.
- Administration timing: Oral doses work best given before the first meal of the day; absorption is not clinically significantly affected by food intake or anticholinergic agents.
- Monitoring: Monitor the clinical response for the condition being treated – resolution of signs, endoscopic appearance and blood in the feces. Routine laboratory monitoring is not otherwise specified, although serum ALT may be considered during high-dose chronic therapy, following the human manufacturer recommendation.
- Laboratory test interference: Ranitidine can cause a false-positive urine protein result on dipstick testing. H2 blockers should be stopped at least 24 hours before gastric acid secretion testing; consider stopping them at least 24 hours before intradermal allergy testing.
- NSAID-associated ulceration: Ranitidine has been used to prevent NSAID-associated ulceration, but efficacy for that purpose has not been demonstrated; where an H2 blocker is chosen for NSAID-related gastrointestinal injury, famotidine or ranitidine may be the best choices, since cimetidine may inhibit the microsomal enzymes that metabolize some NSAIDs.
- Anaphylaxis: Ranitidine has been listed among antihistamine options for localized anaphylaxis.
- Extra-label status: There are no veterinary-labeled ranitidine products, so all use in dogs and cats is extra-label.
- Stability and compounding: The injection is reported stable for up to 48 hours in commonly used intravenous fluids, and tablets have been crushed and mixed with water and syrup with stability for 7 days; protect from freezing.
