Nizatidine — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	2.5-5 mg/kg	q12h (every 12 hours)	Duration: 4-8 weeks for ulcers; as directed for chronic conditions Notes: May be given with or without food. For severe cases, higher doses may be used.
Cat	PO	2.5-5 mg/kg	q12h (every 12 hours)	Duration: 4-8 weeks for ulcers; as directed for chronic conditions Notes: Cats may require higher doses; monitor for efficacy.
Horse	PO	6.6 mg/kg	q24h (every 24 hours)	Duration: 14-28 days for ulcer healing; may be used long-term for prevention Notes: Administer on an empty stomach for optimal absorption. For prevention, may be given before exercise.
Cattle	PO	5-10 mg/kg	q12h (every 12 hours)	Duration: 5-7 days or as directed Notes: Limited data; use with caution in food animals.
Small Ruminants (sheep, goats)	PO	5-10 mg/kg	q12h (every 12 hours)	Duration: 5-7 days or as directed Notes: Limited data; use with caution.
Rabbit	PO	2.5-5 mg/kg	q12h (every 12 hours)	Duration: As directed Notes: Use with supportive care for gastric stasis.

Clinical Indications & Species Uses

General Indications

Treatment of gastric and duodenal ulcers
Management of gastroesophageal reflux disease
Reduction of gastric acid secretion in conditions of hypersecretion

Dog (Canine)

Gastric ulcers
Duodenal ulcers
Esophagitis
Gastroesophageal reflux disease (GERD)
Zollinger-Ellison syndrome (rare)
Prevention of stress ulcers

Cat (Feline)

Gastric ulcers
Esophagitis
Gastroesophageal reflux disease (GERD)
Chronic vomiting associated with gastritis

Horse (Equine)

Gastric ulcers (equine gastric ulcer syndrome)
Prevention of exercise-induced gastric ulcers

Cattle (Bovine)

Abomasal ulcers
Indigestion associated with hyperacidity

Small Ruminants (Sheep / Goat)

Gastric ulcers
Abomasal ulcers

Rabbit & Small Mammals

Gastric ulcers
Gastric stasis (adjunctive therapy)

Exotic & Other Species

Gastric ulcers in ferrets, reptiles (limited data)

Pharmacology & Mechanism of Action

Drug Class: H2 receptor antagonist | Pharmacological Group: Histamine H2-receptor antagonist

Mechanism of Action: Nizatidine is a competitive, reversible inhibitor of histamine at the H2 receptors on gastric parietal cells. By blocking histamine-induced acid secretion, it reduces basal and stimulated gastric acid output, including that stimulated by food, pentagastrin, and insulin. It also decreases pepsin secretion and may increase gastric mucus production, contributing to mucosal protection.

Pharmacodynamics: Nizatidine inhibits both basal and nocturnal gastric acid secretion, as well as acid secretion stimulated by food, caffeine, and other secretagogues. It reduces gastric acid concentration and volume, leading to an increase in gastric pH. The effect is dose-dependent, with a duration of action of up to 12 hours. It does not affect gastric emptying or lower esophageal sphincter pressure significantly.

⚡ Pharmacokinetics Summary

Absorption: Nizatidine is rapidly and well absorbed after oral administration. In dogs, peak plasma concentrations occur within 0.5-2 hours. Food may slightly delay absorption but does not significantly affect the extent of absorption.

Distribution: Nizatidine is widely distributed into body tissues and fluids, including the central nervous system (crosses the blood-brain barrier to some extent). It crosses the placenta and is distributed into milk. The volume of distribution is approximately 1.2-1.5 L/kg in dogs.

Metabolism: Nizatidine undergoes extensive first-pass metabolism in the liver, but the systemic bioavailability is still high (about 70% in dogs). It is metabolized to several metabolites, including N-oxide, S-oxide, and N-desmethyl derivatives, which are less active.

Excretion: Nizatidine is primarily excreted via the kidneys, with about 60-70% of an oral dose appearing in the urine as unchanged drug and metabolites. The remainder is excreted in feces. Renal clearance is high, and dosage adjustment is necessary in animals with renal impairment.

Half-Life: The elimination half-life is approximately 1.5-2 hours in dogs, 1.5-2.5 hours in cats, and 1-2 hours in horses.

Bioavailability: Oral bioavailability is approximately 70% in dogs, 75% in cats, and 60% in horses.

Protein Binding: Nizatidine is approximately 35% bound to plasma proteins.

Available Formulations & Strengths

Oral Capsule 150 mg, 300 mg (PO)

Oral Tablet 75 mg, 150 mg (PO)

Oral Solution 15 mg/mL (PO)

Contraindications & Clinical Warnings

Contraindications:

Known hypersensitivity to nizatidine or other H2 receptor antagonists
Severe renal impairment (requires dose adjustment; if not adjusted, contraindicated)
Use in lactating animals if not necessary (excreted in milk)

Warnings & Clinical Precautions:

Use with caution in animals with hepatic impairment.
Use with caution in animals with renal impairment; reduce dose or increase dosing interval.
May mask symptoms of gastric malignancy; rule out malignancy before treatment.
Use in pregnant animals only if clearly needed; safety not established.
In horses, avoid rapid IV administration (if used IV) to prevent adverse effects.
Long-term use may lead to vitamin B12 deficiency due to reduced acid secretion.
May increase risk of bacterial overgrowth in the stomach due to reduced acidity.

Adverse Effects & Reactions

Common:

Diarrhea
Vomiting
Anorexia
Lethargy
Headache (in humans; not observed in animals)

Serious / Severe:

Hepatotoxicity (rare)
Blood dyscrasias (thrombocytopenia, leukopenia)
Arrhythmias (with rapid IV administration)
Anaphylaxis (rare)

Rare:

Gynecomastia
Impotence (in males)
Confusion (especially in elderly or renally impaired)
Interstitial nephritis

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Antacids	May reduce absorption of nizatidine; separate administration by at least 1 hour.	Mild
Sucralfate	May reduce absorption of nizatidine; separate administration by at least 1 hour.	Mild
Ketoconazole, Itraconazole	Reduced absorption of azole antifungals due to increased gastric pH; monitor antifungal efficacy.	Moderate
Iron salts	Reduced absorption of iron due to increased gastric pH; separate administration.	Mild
Cefpodoxime	Reduced absorption of cefpodoxime due to increased gastric pH; monitor efficacy.	Moderate
Tetracyclines	Reduced absorption of tetracyclines due to increased gastric pH; separate administration.	Moderate
Warfarin	Possible increased anticoagulant effect; monitor coagulation parameters.	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Vomiting
Diarrhea
Lethargy
Ataxia
Tachycardia
Respiratory depression (in severe cases)

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Induce emesis if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Monitor vital signs and provide fluid therapy. In severe cases, provide respiratory support and treat arrhythmias if they occur. There is no specific antidote.

Food Animal Withdrawal Times

🥩 Meat: 7 days🥛 Milk: 3 days

Withdrawal times are not officially established for nizatidine in food animals. The values provided are conservative estimates based on pharmacokinetic data. Consult regulatory authorities for specific requirements.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25°C, 68-77°F).

Handling & Special Conditions: Protect from moisture. Keep container tightly closed.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use.

Extra-Label (Off-Label) Use: In the US, nizatidine is not FDA-approved for veterinary use; however, it may be used in an extra-label manner under the Animal Medicinal Drug Use Clarification Act (AMDUCA) when a veterinarian establishes a valid veterinarian-client-patient relationship and if no approved animal drug is available. Extra-label use in food animals requires a withdrawal period and may be prohibited in certain species (e.g., lactating dairy cattle) if residues are a concern.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Nizatidine is a potent H2 receptor antagonist used in veterinary medicine primarily for the treatment of gastric and duodenal ulcers, esophagitis, and gastroesophageal reflux disease. It is generally well-tolerated, with a wide safety margin. In dogs and cats, it is often used as an alternative to omeprazole or famotidine. In horses, it is effective for equine gastric ulcer syndrome, but may be less potent than proton pump inhibitors. Dosing should be adjusted in animals with renal impairment. Clinical monitoring should include assessment of clinical signs and possibly endoscopic evaluation for ulcer healing. Long-term use may require monitoring of vitamin B12 levels. Always consider the underlying cause of ulceration (e.g., NSAID use, stress) and address it appropriately.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)