Ranitidine for Veterinary Use

Therapeutic Class: Histamine H2 Receptor Antagonist and Prokinetic

Species: Dogs, Cats, Horses

May Be Prescribed For: Treatment or prophylaxis of ulcers

Ranitidine is a histamine H2 receptor antagonist which is used to treat and prevent ulcers of the gastrointestinal tract. Other drugs in this family include cimetidine and famotidine. 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. They are effective in treating the symptoms of ulcers, and in preventing ulcers from occurring in those at risk. These drugs are metabolized in the liver and excreted in the urine.

Ranitidine 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 such as NSAIDs or corticosteroids, and stress. Ranitidine is used to protect against hyperhistaminemia in animals with mast cell tumors, and hypersecretion of gastric acids in animals with gastrinoma.

Ranitidine also has prokinetic properties and may be used to stimulate gastric and colonic emptying. The mechanism of action is through the inhibition of acetylcholinesterase. Because of its promotile effects, ranitidine may be helpful in patients in vomiting animals, particularly if delayed gastric emptying is suspected.

Ranitidine 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. Studies indicate that there is some individual variability in uptake and bioavailablity of H2 receptor antagonists in both adult horses and foals. This may partially explain why some animals appear to respond well, and others do not. Foals and racehorses are two populations with a higher risk for gastric ulcers. Histamine H2 receptor antagonist drugs are sometimes prescribed as a precaution or preventative when an animal is prescribed non-steroidal anti-inflammatory drugs (NSAIDS), corticosteroids, or other drugs that can cause stomach ulcers. Histamine H2 receptor antagonists are frequently used with other drugs such as sucralfate.

• Ranitidine 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. Ranitidine 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 injection

• 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.

• Ranitidine is found at increased concentration in human breast milk.

• Ranitidine has fewer drug interactions than cimetidine.

• The absorption of ranitidine and other histamine H2 antagonists may be affected by antacids. Separate oral administration by 2 hours if possible.

• Drugs for which absorption may be decreased by ranitidine are ketoconazole, itraconazole and vitamin B-12.

• Ranitidine may decrease the metabolism of acetaminophen.

• Propantheline bromide delays the absorption, but increases the blood levels of ranitidine.

• Ranitidine may increase the half-life and peak levels of metoprolol. Ranitidine may increase the bioavailablity of nifedipine. It may also increase blood levels of procainamide.

• Ranitidine 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.