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 of gastric acid – such as hydrochloric acid (HCl) – is well-suited to wild horses, who spend 16-20 hours per day foraging for food.

However, in domestic management settings, horses may go for long periods between meals and eat a grain-based diet. The constant production of gastric juices can result in damage to your horse’s stomach if it is not protected with a steady supply of saliva and forage. [1]

Several other factors contribute to the development of ulcers including: [1]

  • Diet composition (feeding grain that is high in starch and sugar)
  • Feeding regimen (interrupted access to forage)
  • High-intensity exercise
  • Environmental changes
  • Social stress
  • Anti-inflammatory drug use (i.e. NSAIDs)

Types of Gastric Ulcers in Horses

Equine Gastric Ulcer Syndrome (EGUS) refers to ulcers that form in the stomach. [1] EGUS is a common problem in horses and foals. [2]

In horses, gastric ulcers can occur in the following parts of the stomach: 1) the non-glandular (squamous mucosa) tissue that comprises the upper third of the organ and 2) the glandular tissue in the lower portion. [1]

Types of gastric ulcer disease in horses include:

Equine Squamous Gastric Disease (ESGD)

ESGD refers to lesions that occur in the squamous portion of the equine stomach. [1] This area of the stomach lacks the thick, protective mucus and bicarbonate (a pH buffer) layer that is present in the glandular region and is vulnerable to ulceration from gastric acid.

ESGD typically occurs when the mucosal lining of the squamous region has been exposed to highly acidic gastric acid. The squamous mucosa is easily susceptible to damage from constantly secreted gastric acid.

Equine Glandular Gastric Disease (EGGD)

EGGD refers to ulceration in the glandular region of the horse’s stomach. [1] This region is better protected against ulcers than the squamous region.

Equine Glandular Gastric Disease was previously less recognized than ESGD because the original endoscopes used in horses were not long enough to visualize the bottom part of the stomach (pyloric antrum) where most glandular ulceration occurs.

Signs & Symptoms of Ulcers

The observation of symptoms does not always correlate to the severity of ulcers. Horses with minimal ulceration may show significant clinical signs and those that are severely affected may show few or no clinical signs.

Common signs and symptoms of ulcers include: [1]

Diagnosis

Your veterinarian can provide an accurate diagnosis of ulcers by performing a gastroscopy on your horse. [1][2] This is the only definitive way to diagnose the type and severity of ulcers.

Gastroscopy requires passing a small, flexible tube containing a camera into the esophagus, stomach, and upper intestine to examine the tissues. A gastroscope enables your veterinarian to determine where the ulcers are located in the stomach.

Your veterinarian will assess the severity of lesions and may assign a numerical grade that describes the mucosal appearance at different anatomic sites. [1]

However, due to the costs associated with gastroscopy and the very high prevalence of ulcers, some owners choose to proceed with ulcer treatment for their horses without having a gastroscopy performed.

If you notice your horse exhibiting any potential signs of ulcers, contact your veterinarian for advice. Even if your horse is not diagnosed with ulcers, you can implemented strategies to prevent ulcers as part of your horse’s everyday routine.

Treatments for Equine Gastric Ulcers

In addition to ranitidine, medications commonly used to treat stomach ulcers in horses include omeprazole, cimetidine, sucralfate, misoprostol, antacids, and mucosal protectants. [1]

Omeprazole: This medication is a proton pump inhibitor (PPI) that decreases the amount of acid produced by the stomach. [1] Omeprazole is available as Gastrogard (for treatment) or as UlcerGard (for prevention).

GastroGard is the FDA-approved treatment for EGUS and is restricted to use with a prescription issued by a licensed veterinarian. Gastrogard and UlcerGard contain the same amount of omeprazole per gram but are administered at different doses.

Cimetidine: This medication is a histamine H2-receptor antagonist that inhibits the production of stomach acid. [3] Cimetidine is less effective than ranitidine. [16]

Misoprostol: A medication typically used to treat EGGD, misoprostol is a synthetic chemical compound that is similar to natural prostaglandin E1. It inhibits the secretion of gastric acid and enhances mucosal resistance to injury. [4]

Sucralfate: A well-studied mucosal protectant, this medication is a sucrose sulfate-aluminum complex. Sucralfate promotes gastric healing by adhering to ulcerated tissue, stimulating mucous secretion, promoting the synthesis of a natural anti-inflammatory chemical (prostaglandin E2), and enhancing blood flow. [1]

Antacids: Substances such as magnesium hydroxide, aluminum hydroxide, and bismuth subsalicylate are antacids that can help to temporarily reduce ulcer symptoms. [1] A dose of antacid only helps to neutralize stomach acid for two hours or less.

Mucosal Protectants: Pectin-lecithin complexes provide a physical barrier between the gastric mucosa and acid but are not proven to be an effective treatment for ulcers. [1] However, one study found that feeding horses a combination of an antacid (magnesium hydroxide), a pectin-lecithin complex, and yeast (Saccharomyces cerevisiae) may help to prevent ESGD and EGGD. [5]

If you suspect your horse has ulcers, contact your veterinarian to have your horse evaluated. Your veterinarian can help you better understand available treatment options, and how to minimize the risk of ulcer recurrence.

Prevention of Ulcers

Treating gastric ulcers in your horse can be costly and take time. The possibility of ulcer recurrence is also high unless you take action to prevent the condition through proper diet and management strategies.

Feeding your horse a forage-based diet, ensuring they have constant access to feed and water, and avoiding exercise on an empty stomach can significantly reduce ulcer risk.

You can also support your horse’s gut health by feeding Mad Barn’s Visceral+, which was formulated in consultation with veterinarians to support gastric and hindgut health.

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Key benefits of Visceral+:

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Consult with a qualified nutritionist for guidance on changing your feeding program to reduce ulcer risk. You can cubmit your horse’s diet online, and one of our equine nutritionists will provide a complimentary review.

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References

  1. Sykes, BW. et al. European College of Equine Internal Medicine Consensus Statement–Equine Gastric Ulcer Syndrome in Adult Horses. J Vet Intern Med. 2015
  2. Buchanan, BR. et al. Treatment and prevention of equine gastric ulcer syndrome. Vet Clin North Am Equine Pract. 2003
  3. Knych, HK. et al. Disposition of the anti-ulcer medications ranitidine, cimetidine, and omeprazole following administration of multiple doses to exercised Thoroughbred horses. J Vet Pharmacol Ther. 2017.
  4. Van den Boom, R. Equine gastric ulcer syndrome in adult horses. The Veterinary Journal. 2022.
  5. Sykes BW. et al. Efficacy of a combination of Apolectol®, live yeast (CNCM I-1077) and magnesium hydroxide in the management of Equine Gastric Ulcer Syndrome in thoroughbred racehorses: A randomised, blinded, placebo controlled clinical trial. J Eq Vet Sci 2014.
  6. Forney, B. Ranitidine for Veterinary Use. Wedgewood Pharmacy. 2021.
  7. Orsini, J. Gastric ulceration in the mature horse: a review. Journal of Equine Veterinary Education. 2000.
  8. Sykes B.W. A free ride: is long-term omeprazole therapy safe and effective. Br Equine Vet Edu. 2021.
  9. el-Omar, E. et al. Marked rebound acid hypersecretion after treatment with ranitidine. Am J Gastroenterol. 1996.
  10. Murray, MJ. et al. Effects of intermittent feed deprivation, intermittent feed deprivation with ranitidine administration, and stall confinement with ad libitum access to hay on gastric ulceration in horses. Am J Vet Res. 1996
  11. Murray MJ, Schusser GF. Measurement of 24-h gastric pH using an indwelling pH electrode in horses unfed, fed and treated with ranitidine. Equine Vet J. 1993.
  12. Andrews, FM. et al. Efficacy of omeprazole paste in the treatment and prevention of gastric ulcers in horses. Equine Vet J Suppl. 1999.
  13. Lester, GD. et al. Effects of treatment with omeprazole or ranitidine on gastric squamous ulceration in racing Thoroughbreds. J Am Vet Med Assoc. 2005.
  14. Hwang, H. et al. Prevalence and treatment of gastric ulcers in Thoroughbred racehorses of Korea. J Vet Sci. 2022.
  15. Bell, RJW. et al. Equine Gastric Ulcer Syndrome in Adult Horses: A Review. New Zealand Vet. J. 2007.
  16. Ranitidine Monograph. RMTC CTS Monograph Series. 2020.
  17. Uniform Classification Guidelines for Foreign Substances And Recommended Penalties Model Rule. Association of Racing Commissioners International. 2020.