Cimetidine Dosage Calculator for Dogs (Tagamet)

Cimetidine for Dogs – H2 Blocker

Cimetidine is an older H2 receptor antagonist largely replaced by famotidine (longer-acting, fewer interactions) and omeprazole (PPI – more effective).

Dose

5-10 mg/kg PO every 6-8 hours

Dose Reference Table

Weight	Range
5 kg	25-50 mg
10 kg	50-100 mg
20 kg	100-200 mg
30 kg	150-300 mg
40 kg	200-400 mg

Tablets: 200, 300, 400, 800 mg. Tagamet HB 200 mg OTC.

Indications

• GI ulcer prophylaxis
• Gastritis / esophagitis
• Acid reflux
• Acetaminophen toxicity (CYP450 inhibition)
• Mast cell tumor adjunct (histamine effects)
• Stress ulcer prevention

Cimetidine vs Famotidine

Feature	Cimetidine	Famotidine
Dosing	Q6-8H	Q12-24H
Drug interactions	Many (potent CYP450 inhibitor)	Few
Acid suppression	Less	Better
Cost	Similar	Similar
Preferred?	When specific indication	Yes for most

Acetaminophen Toxicity Protocol

1. Cimetidine 5-10 mg/kg q6h x 7 days (CYP450 inhibition)
2. NAC 140 mg/kg loading then 70 mg/kg q6h (primary antidote)
3. SAMe (Denamarin) – hepatic protection
4. IV fluids support
5. Supportive care
6. Particularly important in CATS (very susceptible)

⚠ Drug Interactions (CYP450 Inhibitor)

Check before combining:

• Warfarin – increased anticoagulation
• Propranolol/metoprolol – increased
• Diazepam/midazolam – increased sedation
• Phenytoin – increased
• Theophylline – toxicity risk
• Phenobarbital – increased
• Morphine – increased
• Many others

Side Effects

Common (mild)

• Diarrhea
• Mild GI upset

Uncommon

• Sedation
• Bradycardia (high IV dose)
• Hepatic enzyme elevations

Long-term human use (low dog risk)

• Gynecomastia
• Decreased libido

Frequently Asked Questions

How much cimetidine for my dog?

DOSE: 5-10 mg/kg PO every 6-8 hours

EXAMPLES:

1. 5 kg = 25-50 mg per dose
2. 10 kg = 50-100 mg
3. 20 kg = 100-200 mg
4. 30 kg = 150-300 mg
5. 40 kg = 200-400 mg

TABLETS: 200, 300, 400, 800 mg (Tagamet HB 200 mg OTC). With or without food. Q6-8H dosing inconvenient – FAMOTIDINE often preferred (Q12-24H, fewer drug interactions). For ACETAMINOPHEN TOXICITY: 5-10 mg/kg q6h x 7 days as adjunct to NAC + SAMe + supportive care. Check all medications for interactions before starting (potent CYP450 inhibitor)

Cimetidine vs famotidine – which is better for my dog?

FAMOTIDINE generally PREFERRED. ADVANTAGES of famotidine over cimetidine:

1. ONCE-TWICE daily dosing (vs Q6-8H cimetidine) – better compliance
2. FEWER drug interactions (cimetidine potent CYP450 inhibitor)
3. BETTER acid suppression
4. Less GI motility effect
5. Better safety profile
6. Similar generic cost

WHEN TO USE CIMETIDINE:

1. ACETAMINOPHEN TOXICITY – CYP450 inhibition specifically reduces NAPQI toxic metabolite formation (unique benefit)
2. MAST CELL TUMOR with significant histamine release
3. Famotidine unavailable
4. Specific protocols

WHEN TO USE FAMOTIDINE:

1. Routine acid suppression
2. GI ulcer prophylaxis
3. Gastritis
4. Most situations

WHEN TO USE OMEPRAZOLE (PPI):

1. Severe ulcers
2. Bleeding ulcers
3. Reflux refractory to H2 blockers
4. Mast cell tumor severe
5. NSAID-induced ulcers
6. Most effective acid suppression. Discuss with vet for specific case

Can cimetidine treat acetaminophen poisoning in my dog?

YES – as adjunct to NAC + supportive care. ROLE:

1. Inhibits CYP450 hepatic enzymes
2. Reduces formation of NAPQI (toxic acetaminophen metabolite)
3. Decreases hepatic damage
4. Adjunctive only – NOT primary treatment

ACETAMINOPHEN TOXICITY PROTOCOL:

1. DECONTAMINATION if recent (emesis if conscious within 1-2 hours, activated charcoal)
2. NAC (N-acetylcysteine) – PRIMARY antidote: 140 mg/kg PO loading then 70 mg/kg q6h x 7 doses
3. CIMETIDINE 5-10 mg/kg PO q6h x 7 days (CYP450 inhibition)
4. SAMe (Denamarin) – replenishes glutathione
5. ASCORBIC ACID (vitamin C) 30 mg/kg q6h – antioxidant
6. IV fluids
7. Monitor liver function + methemoglobinemia + Heinz body anemia
8. Hospitalization for supportive care

CATS vs DOGS:

1. CATS extremely susceptible (lack glucuronidation)
2. Dogs less susceptible but still toxic at high doses
3. Earlier treatment = better outcome
4. Time-critical protocol

SIGNS of acetaminophen toxicity:

1. Methemoglobinemia (chocolate-brown mucous membranes, blue gums)
2. Heinz body anemia (RBC damage)
3. Hepatic failure
4. Facial/paw edema
5. Vomiting
6. Hypoxia, weakness. EMERGENCY at any suspected ingestion – immediate vet visit + decontamination + protocol initiation. Don’t delay treatment – hepatic damage progresses

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Related Articles & Guides

Read the in-depth PuppaDogs guides that explain the science and clinical context behind this calculator:

• Cimetidine for Dogs: Benefits, Dosage, Side Effects, and More

References & Further Reading

The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.

1. Plumb DC. Cimetidine.
2. Schmiedt CW et al. H2 blockers in veterinary medicine.
3. Hsu CC. Acetaminophen toxicity management.
4. Marks SL et al. Acid suppression.
5. PuppaDogs. Famotidine Calculator, Acetaminophen Toxicity Calculator. puppadogs.com.