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Famotidine for Dogs, Cats, and Horses

By Barbara Forney, VMD

Last reviewed: 7/13/2022

Commonly prescribed for: Decrease Production of Gastric Acid

Species: Dogs, Cats, and Horses

Therapeutic Class: Histamine H2 Receptor Antagonist

Basic Information

Famotidine is a histamine H2 receptor antagonist that is used to decrease the production of gastric acid within the gastrointestinal tract. In human medicine, this drug is sold under the trade name of Pepcid. Other drugs in this family include cimetidine and ranitidine. These drugs prevent the stomach from producing acid by competitively inhibiting the binding of histamine at the receptor on the parietal cells of the stomach. Studies in human patients show healing of gastric ulcers in patients given either oral ranitidine or oral famotidine.

Famotidine may be administered intravenously, intramuscularly, or orally. Histamine H2 receptor antagonist drugs are metabolized in the liver and excreted in the urine. Unlike cimetidine, famotidine does not significantly inhibit the hepatic P450 enzyme system. It is considered very safe and is the least likely of the histamine H2 receptor antagonist drugs to be involved in drug interactions. Famotidine does not have the prokinetic properties of ranitidine. Relative potencies are: famotidine > ranitidine > cimetidine.

Dogs and Cats

Famotidine is used in dogs and cats to treat or prevent ulcers of the gastrointestinal (GI) tract, and esophagus. Possible causes of GI ulceration include renal failure, drugs, and stress. The primary value of the H 2 receptor antagonists is in treating existing ulcers and erosions. They can be helpful in preventing some types of ulcers, but they are less effective for preventing ulcers due to NSAIDs or corticosteroids.


Famotidine is used in horses to treat and prevent the recurrence of gastric ulcers. Omeprazole is the more-commonly used drug for equine gastric ulcer disease (EGUD), but some clinicians feel that there is also a role for the histamine H2 receptor antagonists.

Side Effects

  • Famotidine and other H2 receptor antagonists are considered very safe drugs with few side effects. They should be used with caution or at a reduced dose in geriatrics or animals with decreased liver or kidney function.
  • Dogs and Cats: Rare: Mild diarrhea, nausea, vomiting, and mental confusion, especially in older patients. Very rare: agranulocytosis (decreased white blood cell count). Rapid intravenous administration has been associated with vomiting and transient cardiac arrhythmia.
  • Horses: No specific information regarding side effects in horses was found. Famotidine has been used in horses for more than 20 years and is generally thought to be a very safe drug.
  • Injection site reactions may occur with intramuscular injections.


  • Histamine H2 receptor antagonist metabolism is decreased in elderly human patients, especially those with kidney or liver disease. It should be used with caution in older animals, and the dose will usually need to be decreased.
  • Famotidine should be used with additional caution in animals with cardiac disease due to possible arrhythmias.
  • There are anecdotal reports of intravascular hemolysis after IV administration to cats.
  • Famotidine is found at increased concentration in human breast milk.

Drug Interactions

  • Famotidine has fewer drug-interactions than cimetidine.
  • The absorption of famotidine and other histamine H2 antagonists may be affected by antacids. Separate oral administration by two hours if possible.
  • Drugs for which absorption may be decreased by famotidine are ketoconazole, itraconazole, and vitamin B-12.
  • Famotidine may decrease the metabolism of acetaminophen.
  • Famotidine may decrease the absorption of some cephalosporin antibiotics and oral iron salts.
  • Histamine H2 receptor antagonists are frequently used with other drugs such as sucralfate.


  • Famotidine and the other H2 receptor antagonist drugs have a wide margin of safety in laboratory animals.
  • Overdose should be treated symptomatically. If oral overdose is recognized promptly, gut emptying protocols may be of benefit.
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