Ranitidine (Zantac) is a medication used to reduce stomach acidity temporarily. [1] It is commonly used in humans and animals to treat peptic ulcers and heartburn.

In horses, this drug is used to alleviate gastric ulcers. Ranitidine is an H2 blocker that works by reducing the amount of acid produced in the stomach, helping to heal ulcers.

Ranitidine is not as effective as other ulcer treatments such as omeprazole, but your veterinarian may recommend it as part of a multi-drug regimen to prevent and treat ulcers.

In April 2020, the FDA ordered the immediate withdrawal of all products containing ranitidine from the US market due to concerns about carcinogens. [16] However, this drug is still available and used in other countries.

In this article, we will discuss how ranitidine works, its effects on gastric ulcers in horses, and alternative treatments that may be more effective for equine gastric ulcers.

Ranitidine for Gastric Ulcers in Horses

Ranitidine is a histamine H2-receptor antagonist that inhibits the production of stomach acid. [6] It is from the same class of drugs as cimetidine and famotidine, which are also used to treat ulcers in horses.

Research shows that 60 – 100% of adult horses in training develop ulcers at some point in their lives. [15] Performance horses are at a high risk of ulcers due to their diets, exercise routines, and management.

Ulcers are sores or lesions that form on the lining of your stomach and intestines. Horses get gastric ulcers when acid erodes the protective lining of the stomach, resulting in tissue damage.

Ranitidine works by reducing the acidity of the stomach, treating ulcer symptoms and giving the horse’s stomach lining time to heal. It can also be given preventatively or to reduce the risk of ulcer recurrence.

Ranitidine is typically administered orally, either as a tablet or in a powdered format. It can also be administered as an intravenous injection.

The dose of ranitidine required to treat gastric ulcers can vary between horses. [6] The bioavailability of ranitidine is generally lower in horses than in humans. [7]

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Mechanism of Action

Ranitidine inhibits or blocks the effects of the immune signalling chemical histamine. A natural chemical in the body, histamine stimulates parietal cells in the stomach to produce stomach acid.

Histamine activates these cells by binding to H2 receptors. This activation causes the parietal cells to produce more acid, which can lead to the development of gastric ulcers.

H2-antagonists including ranitidine reduce stomach acid production by blocking the action of histamine on these receptors, reducing the amount of acid that is produced.

Effectiveness

Multiple studies confirm that ranitidine can suppress stomach acid production in horses, but that it is less effective than omeprazole at relieving gastric ulcers. [12]

A study of five adult horses found that ranitidine suppresses gastric acidity in horses when they have free access to hay. The drug exerted less of an effect in horses that were unfed. [11]

A study of eight horses undergoing alternating periods of feed deprivation resulted in erosion and ulceration of the gastric squamous epithelial mucosa of each horse. Concurrent treatment with ranitidine resulted in significantly fewer areas of ulceration in the gastric squamous epithelial mucosa. [10]

A study of 60 thoroughbreds involved in race training and diagnosed with gastric squamous mucosal ulceration determined that omeprazole was more effective than ranitidine in healing the condition. [13]

Another study of 49 Korean thoroughbred racehorses also found that omeprazole was more effective than ranitidine. [14]

In some cases, the failure of ranitidine for treating ulcers in horses may be attributed to incorrect dosing and a lack of owner compliance in providing three medication doses each day. [1]

Dosage and Administration

Consult with a licensed veterinarian to determine whether ranitidine is appropriate for your horse. Your veterinarian will provide you with the correct dosage regimen to use.

The recommended dose of oral ranitidine is 6.6 mg/kg of body weight given 3 times daily. It should be administered one hour before a meal. [1]

Ranitidine must be re-administered every 8 hours to maintain efficacy. The terminal serum half-life for this drug is approximately 7.4 hours. [16]

The time required to treat gastric ulcers depends on the number and severity of the lesions present in your horse’s stomach. Typically, veterinarians recommend treating with ranitidine and other medications for a minimum of 3-4 weeks.

Your veterinarian may recommend a follow-up gastroscopy to determine if your horse’s ulcers have healed completely following a course of medication.

Cost of Ranitidine

An advantage of ranitidine compared to Gastrogard (omeprazole) or treating equine gastric ulcers is the lower cost of treatment.

810 g of ranitidine powder costs approximately $65 USD or $88 CAD, providing approximately 90 days of medication at a dosing rate of 9 g per day.

In comparison, a tube (6.15 g, or 6150 mg) of Gastrogard costs approximately $35 USD or $50 CAD. One tube of Gastrogard will last a 500 kg horse for three days.

A typical four-week treatment program will require ten tubes with a minimum cost of $350 USD or $500 CAD.

Adverse Effects

Consult with your veterinarian before administering ranitidine to determine whether this medication is appropriate for your horse.

Ranitidine and other H2 receptor antagonists are considered safe drugs with few side effects. [6] Ranitidine has been used for over 30 years in horses and is generally well tolerated.

Rebound Acid Hypersecretion

Proton pump inhibitors such as omeprazole pose a risk of of rebound acid hypersecretion in horses. After cessation of the drug, horses may begin to produce more gastric acid temporarily, increasing the risk of ulcer recurrence. [8]

Research is needed to determine whether ranitidine increases the risk of acid rebound in horses. Studies in humans show that ranitidine therapy is associated with significant rebound hypersecretion of acid. [9]

This may contribute to the rapid recurrence of symptoms after therapy has been stopped. [9]

Precautions

In the US, ranitidine can only be used on the order of a licensed veterinarian. Ranitidine has not been approved by the FDA for use in horses, but it is commonly used off-label under veterinary supervision.

The use of anti-ulcer medications is regulated by many racing and equestrian sports federations. A withdrawal period may be necessary prior to competition to avoid a drug violation.

Ranitidine is classified as a 5/D drug in the ARCI’s Uniform Classification of Foreign Substances. This classification is for drugs with localized actions and the penalty for use is a written warning issued to the trainer and owner. [17]

Ranitidine should be used with caution in geriatric horses and those with reduced liver or kidney function. [6]

Injection site reactions may occur if the drug is administered via intramuscular injection. [6]

Gastric Ulcers in Horses

Ranitidine can be used as part of a multi-pronged approach to treating gastric ulcers. However, it is not the most effective treatment option available.

Furthermore, many horses treated for ulcers experience recurrence of the condition following the conclusion of treatment. Diet and management changes are usually required to address the root cause and reduce your horse’s overall risk of ulcers.

Ulcers can develop anywhere along the gastrointestinal tract (GI) of the horse. They cause pain and discomfort and can promote behavioural and performance problems. [1]

Horses in training have very high rates Equine Gastric Ulcer Syndrome (EGUS), but pleasure horses are also affected by the condition. [1]

Why do Horses get Ulcers?

Why are domesticated horses at such high risk of gastric ulcers? Unlike the stomachs of other mammals, the horse’s stomach constantly produces acids to break down food, even when they are not eating.

The constant secretion