Cimetidine: veterinary dose and monograph

At a glance

Drug class

Gastrointestinal

Also known as

Tagamet, Cimetidine HCl, Act

Species with doses

Dogs, Cats, Cattle, Horses, Rabbits, Ferrets, Reptiles and Small mammals

General dose range

5–10 mg/kg PO q8h — check the species tables for the indication

Routes

PO, IV

Last reviewed

1 October 2026

Indications

• Gastric/duodenal ulceration and erosive gastritis
• Oesophagitis / reflux
• Hypersecretory states (mast cell tumour histamine, gastrinoma) — adjunct
• Occasional use of its CYP inhibition / immunomodulatory effects

Cimetidine dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Acid suppression / ulcer: Papich 5e: 10 mg/kg q6–8h IV, IM or PO. Plumb’s p.273: 5–10 mg/kg PO or parenterally four times daily (Leib 2008). Short-acting — a proton-pump inhibitor is more effective for significant ulceration. Inhibits hepatic drug metabolism (interactions). Give IV slowly.

Cats

• Acid suppression / gastritis: Papich 5e: 10 mg/kg q6–8h IV, IM or PO. Plumb’s p.273 (DeNovo): 5–10 mg/kg PO q6–8h, or 10 mg/kg q6h as a slow (30-min) IV infusion.

Cattle

• Abomasal ulcers (milk-fed calves): Papich 5e: 100 mg/kg PO q8h in milk-fed calves. Extra-label in food animals — obtain a FARAD withdrawal.

Horses

• Gastric ulceration (adjunct): Papich 5e: 40–60 mg/kg/day PO (≈13–20 mg/kg q8h) — oral results are inconsistent in horses. Plumb’s p.273 (foals): 300–600 mg PO or IV four times daily. Omeprazole is first-line for equine gastric ulcer syndrome. ARCI Class 5. (40–60 mg/kg/day ÷ 3 = 13.3–20 mg/kg q8h.)
• Gastric ulceration (IV): Papich 5e: 3 mg/kg diluted in fluids and infused IV over 2 min q8h.
• Melanoma (adjunct): Plumb’s p.273 (Rashmir-Raven 2006): 48 mg/kg/day PO (interval not specified); regression should be evident within 3 months, otherwise stop. Some horses need lifelong treatment.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Abomasal ulcers (milk-fed calves): Papich 5e: 100 mg/kg PO q8h in milk-fed calves. Extra-label in food animals — obtain a FARAD withdrawal.

Rabbits

• GI ulcers: Plumb’s p.273 (Ivey & Morrisey 2000): 5–10 mg/kg PO, SC, IM or IV q8–12h.

Ferrets

• Stress-induced ulcers: Plumb’s p.273 (Williams 2000): 5–10 mg/kg PO, SC, IM or IV three times daily.

Reptiles

• Gastric acid suppression: Plumb’s p.273 (Gauvin 1993): 4 mg/kg PO q8–12h in most species.

Small mammals

• GI ulcers: Plumb’s p.273 (Adamcak & Otten 2000): mice, rats, gerbils, hamsters, guinea pigs, chinchillas 5–10 mg/kg PO, IM or SC q6–12h.

Contraindications

Caution with the many CYP-metabolised co-medications (see interactions). Significant renal impairment (reduce dose). Rapid IV injection (hypotension/arrhythmia). Known hypersensitivity. PPIs are more effective for serious ulceration.

Species-specific warnings

Horses: Omeprazole is first-line for equine gastric ulcer syndrome; cimetidine needs frequent (q8h) high dosing and is less effective.

Adverse effects

• Generally well tolerated
• Many drug interactions (CYP inhibition) — the main practical drawback
• Bradycardia/hypotension with rapid IV
• Rare CNS signs in renal impairment

Drug interactions

• Potent CYP inhibitor: raises levels of many drugs — theophylline, lidocaine, metronidazole, propranolol, phenobarbital, warfarin, ketoconazole, diazepam, etc.
• Antacids: reduce cimetidine absorption (separate)
• Drugs needing acid for absorption (azoles): reduced absorption
• Reduces clearance of procainamide/NAPA

Pregnancy and lactation

Generally considered acceptable; long human safety record. Use if needed.

Monitoring

• Clinical response (ulcer/gastritis resolution)
• Review ALL co-medications for CYP interactions (the key task with cimetidine)
• Renal function (dose adjustment)
• Consider switching to a PPI for inadequate response

Toxicity and overdose

Wide direct safety margin; overdose is usually limited to mild effects, with rapid IV occasionally causing hypotension/bradycardia. The dominant clinical risk is not toxicity per se but DRUG INTERACTIONS from CYP inhibition (e.g. precipitating theophylline or lidocaine toxicity).

Management: Supportive; no specific antidote. Slow/stop IV for cardiovascular effects. Manage toxicity of interacting drugs whose levels may have risen.

Clinical pearls

• The weakest H2-blocker and a strong CYP inhibitor — famotidine (fewer interactions) or omeprazole (more effective) are usually better choices for acid suppression
• Its main "feature" is the long interaction list — always check co-meds (theophylline, lidocaine, metronidazole, etc.) before using it
• Useful for histamine-driven hypersecretion (mast cell tumours) as an adjunct
• Give IV slowly; q8h dosing reflects its short duration

Mechanism of action

Competitively blocks histamine H2 receptors on gastric parietal cells, reducing histamine-stimulated acid secretion and raising gastric pH. Separately, it potently inhibits several hepatic cytochrome-P450 enzymes (and reduces hepatic blood flow), which slows metabolism of many co-administered drugs — the basis of its extensive interaction profile and occasional deliberate use to prolong other drugs' effects.

Formulations and products

• 200 / 400 mg tablet
• Injection 150 mg/mL
• Tagamet / Act — 200 / 400 mg tablet; 150 mg/mL injection, Tablet / injection (human-label)

Storage

Tablets/injection: 15–30 °C, protect from light.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other gastrointestinal drugs

• Activated Charcoal
• Apomorphine
• Bismuth Subsalicylate
• Capromorelin
• Cisapride
• Famotidine
• Hyoscine Butylbromide (N-Butylscopolammonium)
• Lactulose

Frequently asked questions