Cimetidine is an over the counter histamine 2 blocker or histamine H₂ receptor antagonist. It works by inhibiting the production of stomach acid by blocking histamine receptors in the stomach that are responsible for triggering acid production.
It has not been FDA approved for use in animals but is used legally by veterinarians as an extra-label medication.
Cimetidine was the first H₂ receptor antagonist available and sold under the brand name Tagamet, but is also available in generic form. Its use has declined due to newer and improved H₂ receptor antagonists.
In veterinary medicine, cimetidine is used in the prevention or treatment of the following conditions:
Stomach (gastric) ulcers or intestinal ulcers: Build-up of toxins in cats with kidney disease, stressed cats, drug-induced or cats with stomach cancer, Helicobacter infection, ingestion of toxins),
Gastritis (inflammation of the stomach): Dietary indiscretion, ingestion of toxins, foreign bodies, infection.
Mast cell tumours: These tumours which originate from mast cells produce large amounts of histamine.
By blocking the secretion of stomach acid, the cat’s gastrointestinal tract has time to heal from ulcers or inflammation.
Never administer medication unless it has been prescribed by a veterinarian.
Dosage varies from cat to cat; underlying health problems must be taken into consideration when deciding the safe dosage for cats. The typical dose of cimetidine is as follows:
- 5 to 10 mg per kilo
- 3 to 5 mg per pound
Two to four times a day.
Cats receive cimetidine either via injection, oral suspension (liquid) or tablet. Tablets come in 100 mg, 200 mg, 300 mg, 400 mg and 800 mg.
Administer on an empty stomach as giving it with a meal will cause stomach acid secretion and reduce its effectiveness.
Always follow your veterinarian’s instructions and avoid the following:
- Giving a larger dose than prescribed
- Administering cimetidine more often than prescribed
- Skipping a dose
If your cat does miss a dose, symptoms may return, so it is important to remember to give the cat the medication, as directed.
Cimetidine can inhibit cytochrome P450 enzymes which are responsible for the metabolism and clearance of many drugs. The following medications may be affected by cimetidine:
- Warfarin (blood thinner)
- Beta-blockers (to treat heart disease)
- Calcium channel blockers (to treat heart disease)
- Lidocaine (local anesthetic)
- Diazepam and other benzodiazepines (tranquilisers)
- Quinidine (antiarrhythmic agent)
- Metronidazole (antibiotic)
- Theophylline (an airway dilator)
- Tricyclic antidepressants
Your cat’s veterinarian may recommend that doses be staggered if the cat is receiving both cimetidine and metoclopramide, antacids, ketoconazole, sucralfate or digoxin.
What happens if I miss a dose?
Administer as soon as possible; however, if it is close to the time for your cat’s next dose, do not administer, wait until the scheduled time. Never exceed the total stated dose.
If your cat does accidentally receive a double dose, ensure you contact the veterinarian for advice.
Do not give to cats with a known hypersensitivity to the drug.
Use with caution in geriatric cats, cats with cardiac disease, impaired liver or kidney function and only under the close supervision of a veterinarian. Confusion has occurred in humans who meet the above criteria. A dose reduction may be necessary.
Tell your veterinarian if you suspect your cat may be pregnant, lactating or is on any other medications, supplements or vitamins.
Side effects to cimetidine are rare but can include allergic reaction, which can include the following symptoms:
- Facial swelling
- Urticaria (rash)
Pain at the injection site in cats who receive cimetidine via injection
Store at room temperature, and protect from light and humidity. Keep human and pet medication in separate containers to avoid mixing medications and accidental administration.
- Famotidine (Pepcid)
- Ranitidine (Zantac)
- Nizatidine (Axid)
One trial in humans found that the duration of action of famotidine was 30 percent longer than that of either cimetidine or ranitidine. Famotidine was nine times more potent than ranitidine and 32 times more potent than cimetidine.