# Cimetidine: veterinary dose and monograph

> Cimetidine is a veterinary gastrointestinal drug. A first-generation histamine H2-receptor antagonist that reduces gastric acid — used for gastric/duodenal ulceration, gastritis, oesophagitis and hypersecretory states (e.g. Indications include gastric/duodenal ulceration and erosive gastritis; oesophagitis / reflux; hypersecretory states (mast cell tumour histamine, gastrinoma) — adjunct. This monograph lists 10 reference doses for dogs, cats, cattle, horses, rabbits and ferrets and 2 more species, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

Source: https://vetmasterji.com/drugs/cimetidine · Last reviewed: 2026-10-01

## 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

*Cimetidine doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Acid suppression / ulcer | 5–10 mg/kg | PO | q6–8h | — |

- 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

*Cimetidine doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Acid suppression / gastritis | 5–10 mg/kg | PO | q6–8h | — |

- 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

*Cimetidine doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Abomasal ulcers (milk-fed calves) | 100 mg/kg | PO | q8h | — | Withdrawal NOT established — treat as extra-label |

- 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

*Cimetidine doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Gastric ulceration (adjunct) | 13.3–20 mg/kg | PO | q8h | — |
| Gastric ulceration (IV) | 3 mg/kg | IV | q8h | — |
| Melanoma (adjunct) | 48 mg/kg | PO | total daily dose | until 2–3 weeks after tumour growth resolves |

- 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.

*Cimetidine doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Abomasal ulcers (milk-fed calves) | 100 mg/kg | PO | q8h | — | Withdrawal NOT established — treat as extra-label |

- 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

*Cimetidine doses for rabbits*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| GI ulcers | 5–10 mg/kg | PO | q8–12h | — |

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

### Ferrets

*Cimetidine doses for ferrets*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Stress-induced ulcers | 5–10 mg/kg | PO | q8h | — |

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

### Reptiles

*Cimetidine doses for reptiles*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Gastric acid suppression | 4 mg/kg | PO | q8–12h | — |

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

### Small mammals

*Cimetidine doses for small mammals*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| GI ulcers | 5–10 mg/kg | PO | q6–12h | — |

- 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

> **Caution:** 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

> **Caution:** 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.

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## Frequently asked questions

### What is the dose of Cimetidine for dogs?

Reference doses for Cimetidine in dogs: 5–10 mg/kg PO q6–8h (Acid suppression / ulcer). Confirm against the label and the patient before use.

### What is the dose of Cimetidine for cats?

Reference doses for Cimetidine in cats: 5–10 mg/kg PO q6–8h (Acid suppression / gastritis). Confirm against the label and the patient before use.

### What is the dose of Cimetidine for cattle?

Reference doses for Cimetidine in cattle: 100 mg/kg PO q8h (Abomasal ulcers (milk-fed calves)). Confirm against the label and the patient before use.

### What is the withdrawal period for Cimetidine?

Cattle, PO (Abomasal ulcers (milk-fed calves)): Withdrawal NOT established — treat as extra-label. Follow the product label and national regulations where they differ.

### When should Cimetidine not be used?

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.

### What are the side effects of Cimetidine in animals?

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

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.