Cimetidine

Cimetidine is a histamine H2-receptor antagonist that reduces gastric acid secretion. It is an older acid-suppressive agent historically used in veterinary patients with acid-related upper gastrointestinal disease. Its short duration of effect and comparatively modest acid suppression have reduced its clinical role as more effective agents have become available.

Group

Histamine H2 antagonist

Mechanism of Action

Cimetidine competitively blocks histamine H2 receptors on gastric parietal cells. This reduces histamine-stimulated cyclic-AMP signaling and activation of the acid-secretory machinery, decreasing basal and stimulated gastric acid output. The resulting increase in gastric pH reduces acid exposure of damaged mucosa. Its main therapeutic action is acid suppression rather than stimulation of gastrointestinal motility or direct inhibition of emesis.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	10 mg/kg	IV, IM, PO	Every 6–8 h
Gastric acid suppression	5–10 mg/kg	PO	Every 6 h
Historical immunomodulation	10–25 mg/kg	PO	Every 12 h	Empirical use to oppose suppressor-T-cell effects; clinical evidence is limited.

Cats

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	10 mg/kg	IV, IM, PO	Every 6–8 h
Gastric acid suppression	5–10 mg/kg	PO	Every 6–8 h
Gastric acid suppression	10 mg/kg	IV	Every 6 h	Infuse slowly over 30 minutes.

Horses

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	3 mg/kg	IV	Every 8 h	Dilute in fluid and infuse over 2 minutes.
Oral gastric acid suppression	Reference only	PO		40–60 mg/kg total daily orally; number of daily divisions is not specified and response is inconsistent.
Foal acid suppression	Reference only	PO		Foals: 1000 mg total daily divided twice or three times daily by PO/IV/IM routes; alternatively 300–600 mg per administration PO or IV four times daily. These are separate fixed-dose alternatives with limited clinical evidence.
Melanoma adjunct	Reference only	PO		48 mg/kg total daily orally; division interval is not assigned. A historical response trial continues 2–3 weeks beyond resolution, but no regression by three months suggests lack of benefit.

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Abomasal ulcer treatment	100 mg/kg	PO	Every 8 h	Calves only. Milk-fed calves.

Ferrets

Use / stage	Dose	Route	Schedule	Instructions
Stress-associated ulcer treatment	5–10 mg/kg	PO, SC, IM, IV	Every 8 h

Rabbits

Use / stage	Dose	Route	Schedule	Instructions
Gastrointestinal ulcer treatment	5–10 mg/kg	PO, SC, IM, IV	Every 8–12 h

Mice

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	5–10 mg/kg	PO, IM, SC	Every 6–12 h

Rats

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	5–10 mg/kg	PO, IM, SC	Every 6–12 h

Gerbils

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	5–10 mg/kg	PO, IM, SC	Every 6–12 h

Hamsters

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	5–10 mg/kg	PO, IM, SC	Every 6–12 h

Guinea pigs

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	5–10 mg/kg	PO, IM, SC	Every 6–12 h

Chinchillas

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	5–10 mg/kg	PO, IM, SC	Every 6–12 h

Pigs

Use / stage	Dose	Route	Schedule	Instructions
Gastric ulcer treatment	Reference only	PO		300 mg per animal twice daily; the dosage bullet does not explicitly assign a route.

Reptiles

Use / stage	Dose	Route	Schedule	Instructions
Gastric acid suppression	4 mg/kg	PO	Every 8–12 h

Indications

Historically, acid suppression as part of treatment for suspected acid-related gastric or duodenal ulceration in dogs and cats; veterinary evidence for reliable ulcer healing is limited.
Adjunctive reduction of acid exposure in reflux esophagitis.
Management of gastric hypersecretion associated with gastrinoma or systemic mast-cell disease in selected veterinary patients.
Historically, treatment of gastric or abomasal ulceration in large animals; clinical efficacy is incompletely established.

Contraindications

Use cautiously with renal impairment or medicines dependent on hepatic metabolism.

Interactions

CYP450 inhibition can increase exposure to other drugs.
Raised gastric pH reduces absorption of ketoconazole, itraconazole and iron.

Adverse effects

Possible central nervous system effects at high exposure

Preparations

Preparation	Form	Strength	Route
Cimetidine 100 mg tablet	Tablet	100 mg / tablet	PO
Cimetidine 150 mg tablet	Tablet	150 mg / tablet	PO
Cimetidine 200 mg tablet	Tablet	200 mg / tablet	PO
Cimetidine 300 mg tablet	Tablet	300 mg / tablet	PO
Cimetidine 400 mg tablet	Tablet	400 mg / tablet	PO
Cimetidine 800 mg tablet	Tablet	800 mg / tablet	PO
Cimetidine 60 mg/mL oral liquid	Oral Liquid	60 mg / mL	PO
Cimetidine 150 mg/mL injection	Injection	150 mg / mL	IV, IM

Monitoring and Administration

Veterinary ulcer-healing efficacy is not well established; vomiting alone and prevention of NSAID injury are not supported indications.

For equine ulcers, other agents are preferred because acid suppression and clinical results are inconsistent.

Do not refrigerate the described injectable formulation; compatible solutions retain potency for at least 14 days.

A 60 mg/mL suspension made with glycerin/simple syrup has reported 17-day potency at 4°C. This refrigerated oral preparation is distinct from the injection, which should not be refrigerated.