Gastrobim® (Generic Omeprazole) for Horses: Uses, Side Effects & Status in Competition

Gastrobim^® is a prescription omeprazole oral paste used in horses for the treatment of gastric ulcers and prevention of ulcer recurrence. Omeprazole reduces stomach acid, helping create conditions that support healing of ulcerated tissue in the stomach lining.

Equine Gastric Ulcer Syndrome (EGUS) is highly prevalent in horses, particularly those exposed to intensive training, competition travel, stall confinement, and feeding practices that differ from natural grazing behavior.

As a proton pump inhibitor, omeprazole suppresses gastric acid production. This makes Gastrobim^® part of veterinary treatment plans for equine gastric ulcers, alongside management changes that address underlying risk factors.

Continue reading to learn more about Gastrobim^® for horses, including how it works, when it may be used, and its role in a comprehensive approach to EGUS management.

Gastrobim^® (Omeprazole) for Horses

Gastrobim^® is a prescription oral paste formulation of omeprazole produced by Bimeda Animal Health Limited and used for the treatment of gastric ulcers in horses.

Omeprazole is a proton pump inhibitor that lowers acid production in the equine stomach, helping protect the squamous, skin-like lining from irritation and ulcer formation.

Gastrobim^® was approved in April 2026 after the FDA determined it had the same effect as Gastrogard^® and Ulcergard^®, the currently approved formulations produced by Boehringer Ingelheim^®. ^[1] Gastrobim^® is approved for both treatment and prevention of gastric ulcers in horses. ^[1]

GastroGard^® was the original FDA-approved omeprazole paste specifically labeled for the treatment of equine gastric ulcer syndrome (EGUS).

UlcerGard^®is another over-the-counter omeprazole product labeled for the prevention of gastric ulcers in at-risk horses.

Although both products share the same active ingredient, their approved indications, dosing regimens, and marketing claims differ. Gastrobim^® enters this market as a prescription generic alternative to both GastroGard^® and Ulcergard^®, as Gastrobim^® has both prevention and treatment indications on its label. ^[1]

Available Forms

Gastrobim^® is supplied as an apple-flavored omeprazole oral paste in an adjustable-dose syringe. It is an FDA-approved generic formulation used for the treatment of gastric ulcers and prevention of ulcer recurrence in horses.

Generic drugs are a copy of a brand name drug that is bioequivalent. This means it contains the same ingredients, in the same amounts, and at a similar dosage to the brand name medication. ^[3] These medications are still regulated by Health Canada and the FDA to ensure they are safe and effective.

Generics are often available at a lower cost than brand name medications. As of this writing, prices for Gastrobim^® in the United States have not been published.

Other omeprazole products used in equine medicine include: ^[4]

• GastroGard^®: A branded omeprazole oral paste approved for the treatment of gastric ulcers in horses.
• UlcerGard^®: An omeprazole oral paste labeled for prevention of gastric ulcers in horses at a lower dose rate than treatment products.
• Generic omeprazole: Compounded omeprazole products may be used in some circumstances under veterinary direction.
• Prilosec^®/Losec^®: Human brand names for omeprazole, not labelled for horses.

Veterinarians may use human-labeled oral formulations of omeprazole in select cases, including tablets, capsules, or liquid suspensions. ^[4]

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Drug Class: Proton Pump Inhibitors

Proton pump inhibitors are a group of drugs that act on proton pumps, transporters that move hydrogen ions into the stomach for acid production. By inhibiting the pumps, fewer hydrogen ions enter the stomach, making it less acidic. ^[4]

Omeprazole is the most widely used proton pump inhibitor in both human and veterinary medicine. In equine practice, it is commonly used for treatment and prevention of conditions associated with excess gastric acid, including Equine Gastric Ulcer Syndrome.

Other proton pump inhibitors used in veterinary medicine include: ^[5]

• Esomeprazole
• Pantoprazole

Mechanism of Action

Omeprazole reduces gastric acid secretion by irreversibly inhibiting hydrogen–potassium ATPase enzymes, also known as proton pumps, located on the surface of acid-producing cells in the stomach. ^[5]

These enzymes are responsible for the final step in acid production, transferring hydrogen ions into the stomach lumen. When omeprazole binds to an active pump, acid secretion from that pump is effectively shut down. ^[6]

Because this interaction is irreversible, acid production can only resume once new proton pumps are synthesized and inserted into the cell membrane. This explains the prolonged acid-suppressing effect of omeprazole compared to other classes of antacid medications.

By lowering gastric acidity, omeprazole helps limit ongoing acid exposure to the stomach lining and supports conditions that allow ulcerated tissue to heal. In horses, reduced stomach acid production typically lasts for approximately 27 hours following administration. ^[4]

Uses in Horses

Gastrobim® is FDA-approved for treating gastric ulcers in horses. Gastric ulcers develop when the protective lining of the stomach is disrupted, leading to erosion and ulceration.

Horses produce gastric acid continuously, regardless of whether they are eating, which makes the stomach particularly vulnerable when natural buffering mechanisms are reduced.

EGUS is generally divided into two categories based on the region of the stomach affected. Equine Squamous Gastric Disease (ESGD) occurs in the upper, non glandular portion of the stomach, which lacks protective mucus and is more susceptible to acid exposure. ^[4][7]

Equine Glandular Gastric Disease (EGGD) affects the lower, glandular portion, where acid is normally produced and protective mechanisms are more complex. Omeprazole can be used to treat both types of gastric ulcers, although it is less effective at treating glandular ulcers. ^[4][7]

Equine risk factors for developing gastric ulcers include diet, exercise, management, medication use, and stress-related factors. ^[8]

• Intense exercise, especially for horses involved in racing or competition
• High-grain diets
• Limited forage availability or long periods without hay or pasture
• Intermittent feeding schedules
• Stress from travel, competition, stall confinement, or changes in routine
• Limited turnout or social isolation
• Use of non-steroidal anti-inflammatory drugs (NSAIDs), such as phenylbutazone (bute)
• Illness, injury, hospitalization, or reduced appetite
• Previous history of gastric ulcers

Clinical signs of gastric ulcers in horses include: ^[10]

• Poor appetite
• Weight loss
• Girth sensitivity
• Behavior changes
• Poor performance
• Recurrent mild colic

Off-Label Uses

According to the product label, Gastrobim^® is not recommended for foals under 4 weeks of age or horses weighing less than 70 kg. ^[14] Use in younger or smaller foals would therefore be considered off-label or extra-label and should only occur under direct veterinary supervision.

Veterinarians may also use omeprazole off-label in cases where a horse’s age, body weight, pregnancy status, lactation status, dose, duration, or clinical condition falls outside the product label.

For example, the use of Gastrobim^® in pregnant or lactating mares is not recommended due to limited safety data, and the product is not permitted for use in mares producing milk for human consumption. ^[14]

Off-label prescribing is a routine and accepted aspect of veterinary medicine when a veterinarian determines that treatment is appropriate for an individual animal. In these cases, the veterinarian determines the dose, duration, monitoring plan, and withdrawal considerations based on the horse’s condition, available evidence, and clinical judgment.

Administration Routes

Gastrobim^® is an oral paste formulation of omeprazole for horses. The medication is supplied in a single-dose syringe, with a plunger that can be adjusted based on the horse’s body weight. The syringe is inserted into the horse’s mouth to dispense the medication. Gastrobim^® is apple-flavored to improve palatability.

For optimal absorption, omeprazole should be administered on an empty stomach, ideally at least 30 minutes before feeding. ^[4] Administering the drug with feed can significantly reduce absorption, with studies showing decreases of up to 67%. ^[4]

Formulations of omeprazole vary in how effectively the drug is protected from degradation in the stomach and absorbed in the small intestine. Established products such as GastroGard^® and UlcerGard^® use enteric coating to improve bioavailability. ^[4]

Gastrobim^® does not have enteric coating, but it has been shown to be bioequivalent to these formulations, meaning it delivers a comparable amount of active drug at a similar dose. ^[4] Other generic omeprazole products without protective mechanisms may have reduced absorption in horses.

Dosage

Gastrobim^® is approved for both treatment and prevention of gastric ulcers in horses. The recommended dose varies depending on the intended use: ^[1]

• Treatment: 4 mg/kg by mouth every 24 hours for 4 weeks
• Prevention: 2 mg/kg by mouth every 24 hours for 4 weeks

These doses are similar to those recommended for UlcerGard^® and GastroGard^®. Your veterinarian may recommend other dosages or durations of administration based on your horse’s condition. Follow your veterinarian’s guidance when administering omeprazole.

Storage

Gastrobim^® should be stored below 30°C and the cap should be replaced securely after each use. Proper storage helps protect the product from heat, air exposure, and contamination after the tube has been opened. ^[14]

Unopened tubes have a shelf life of 2 years when packaged for sale. After first opening, the tube should be used within 28 days, and any remaining product should be discarded after this period. Do not use Gastrobim^® past the expiry date printed on the packaging. ^[4][14]

Safety Warnings & Precautions

Gastrobim^® is generally well-tolerated in horses, with few reported side effects. It can be safely used in foals as young as 4 weeks of age. Always follow your veterinarian’s recommendations when using omeprazole.

The manufacturer states that although no treatment-related clinical adverse effects are known, hypersensitivity reactions are still possible. Treatment should be stopped immediately if signs of hypersensitivity occur. ^[14]

People administering Gastrobim^® should avoid direct contact with the skin and eyes, wear impervious gloves, and wash hands or exposed skin after use. If the product contacts the eyes, rinse immediately with clean running water and seek medical advice. Individuals who develop a reaction after handling the product should avoid future contact. ^[14]

Monitoring

Owners should monitor horses on Gastrobim^® for any changes in behavior, appetite, or signs of discomfort during treatment. Veterinarians may use endoscopy (passing a camera into the stomach) to monitor the efficacy of omeprazole treatment. This allows them to visualize the horse’s ulcers and track progress towards healing. ^[4]

Horses may experience a rebound effect after discontinuing proton pump inhibitor use. This effect is well-known in humans and is thought to result from reduced stomach acidity. Under normal conditions, an acidic gastric environment inhibits the release of gastrin, a hormone that stimulates acid production. ^[10] When omeprazole raises gastric pH, this inhibitory feedback is reduced, leading to increased gastrin secretion as the body attempts to restore normal acidity.

Following abrupt cessation of treatment, elevated gastrin levels can rapidly stimulate gastric acid production, resulting in a period of hyperacidity. ^[10] This rebound acid hypersecretion may contribute to ulcer formation or the recurrence of clinical signs after treatment ends.

For this reason, human medical guidelines recommend gradually reducing the dose of proton pump inhibitors, allowing gastrin levels to normalize before complete withdrawal.

In horses, early research suggests that gastrin concentrations may return to baseline relatively quickly after sudden discontinuation of omeprazole. ^[10] However, it remains unclear whether this normalization fully eliminates the risk of ulcer recurrence, and further investigation is needed.

As a precaution, many veterinarians currently advise tapering omeprazole doses following prolonged use, with the goal of minimizing the potential for rebound hyperacidity.

Contraindications

Contraindications refer to circumstances where a drug should be avoided or used with caution.

Gastrobim^® should not be used in horses with known hypersensitivity to omeprazole, other proton pump inhibitors, or any of the product’s excipients. Treatment should be discontinued if signs of a hypersensitivity reaction occur. ^[14]

Gastrobim^® is not recommended for foals under 4 weeks of age or horses weighing less than 70 kg. It should also be used with caution in horses with liver or kidney disease. ^[14]

The safety of Gastrobim^® has not been determined for pregnant or lactating mares, and use in these animals is not recommended. Gastrobim^® should not be used in mares producing milk for human consumption. ^[14]

The manufacturer also advises that veterinarians consider whether diagnostic testing is needed before treatment. Because stress, feeding practices, management, and intensive training can contribute to gastric ulceration, treatment should be combined with management changes where appropriate, such as reducing stress and fasting, increasing roughage intake, and improving access to grazing. ^[14]

Side Effects

Omeprazole is generally well-tolerated in horses, with few reported side effects at labeled doses. However, long-term use of omeprazole in humans is associated with several conditions.

Known effects in humans include: ^[11]

• Osteoporosis, including increased risk of fractures
• Acute kidney inflammation
• Clostridioides difficile-associated diarrhea
• Low blood magnesium
• Vitamin B12 deficiency

It is unknown whether horses have a higher risk of these conditions when being treated with omeprazole. One study noted a potential decrease in calcium absorption from the diet, but clinical significance could not be determined. ^[12]

In general, veterinarians use the shortest duration of treatment possible and avoid long-term use of the drug to mitigate the risks of long-term effects. Treatment for up to 90 days in horses is considered safe. ^[4]

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Acute Toxicity (Overdose)

Omeprazole has a wide margin of safety in horses when used at labeled doses. In safety studies cited by the manufacturer, no treatment-related adverse effects were observed in adult horses and foals older than 2 months given up to 20 mg/kg daily for 91 days. This is five times the standard 4 mg/kg treatment dose. ^[14]

No treatment-related effects on semen quality or reproductive behaviour were observed in breeding stallions given 12 mg/kg daily for 71 days. Adult horses also tolerated 40 mg/kg daily for 21 days without treatment-related adverse effects. ^[14]

Although these data suggest accidental overdose is unlikely to cause acute toxicity in most horses, Gastrobim^® should only be administered according to the prescription label or veterinary instructions. Contact your veterinarian if a horse receives more than the prescribed dose or shows unusual signs after administration.

Drug Interactions

Omeprazole has the potential to interfere with liver enzymes involved in drug metabolism and elimination. As a result, it may alter the breakdown or clearance of certain medications, which can affect their blood concentrations and clinical effectiveness.

Drug interactions related to altered metabolism or excretion have been reported with the following medications: ^[4]

• Benzodiazepines, such as alprazolam or diazepam
• Bisphosphonates, such as clodronate
• Cephalosporin antibiotics, such as cephalexin
• Clarithromycin
• Clopidogrel
• Digoxin
• Doxycycline
• Levothyroxine
• Methotrexate
• Mycophenolate
• Warfarin

In addition to its effects on hepatic metabolism, omeprazole’s suppression of gastric acid may influence the digestion and intestinal absorption of certain drugs and nutrients. To reduce the risk of impaired absorption, these products should be administered at least one to two hours before omeprazole.

Substances that may be affected by changes in stomach acidity include: ^[4]

• Vitamin B12
• Azole antifungals, such as itraconazole or ketoconazole
• Iron

Certain medications may also affect omeprazole concentrations by altering its metabolism, potentially changing its effectiveness: ^[4]

• Phenobarbital
• Rifampin

Regulatory Status

Gastrobim^® is an FDA-approved oral paste formulation of omeprazole for use in horses. It is the first approved generic formulation of omeprazole paste in the United States and is indicated for the treatment and prevention of gastric ulcers.

As a generic product, Gastrobim^® was required to demonstrate bioequivalence to the reference drug, GastroGard^®, meaning it delivers the same active ingredient at a comparable rate and extent of absorption when used according to label directions.

FDA approval also requires compliance with manufacturing standards, potency verification, and labeling oversight. This provides assurance that the product meets established safety, quality, and efficacy requirements.

The availability of a generic omeprazole product may improve access to treatment by offering a lower-cost option while maintaining regulatory oversight. Gastrobim^® is a prescription medication and should be used under the direction of a licensed veterinarian.

Status in Competition

Many equestrian competition organizations permit the use of omeprazole, recognizing that factors such as travel, mental stress, and physical exertion commonly increase the risk of gastric ulcer development.

Allowing use of this medication helps ensure horses with gastric ulcer disease receive appropriate management while continuing to compete.

Regulations governing omeprazole use, however, differ considerably between disciplines and governing bodies. ^[13] Some organizations allow same-day administration, while others may prohibit administration on competition day.

Additionally, some may require a formal disclosure of omeprazole use prior to competition. Always check with your competition organization about their policies prior to administering omeprazole.

Frequently Asked Questions

Here are some frequently asked questions about Gastrobim^®, omeprazole, and gastric ulcer treatment in horses:

Summary

Gastrobim^® is the first FDA-approved generic omeprazole paste for horses, offering veterinarians and horse owners a bioequivalent alternative to GastroGard^® for treating equine gastric ulcer syndrome (EGUS).

• Gastrobim^® contains omeprazole, the same active ingredient used in GastroGard^®, and is FDA-approved as a bioequivalent generic
• It is indicated for the treatment of equine gastric ulcers and prevention of ulcer recurrence in horses and foals 4 weeks of age and older
• As the first generic option, Gastrobim^® may provide a more cost-effective alternative for managing EGUS in horses
• Veterinary diagnosis and guidance remain essential to ensure proper ulcer treatment, dosing, and long-term management strategies