Prednisolone for Horses: Uses, Side Effects & Status in Competition

Prednisone and prednisolone are corticosteroid medications used in veterinary medicine to reduce inflammation and suppress abnormal immune responses. Prednisolone is generally preferred in horses because it is the active form of the medication and is absorbed more reliably than prednisone.

These drugs are commonly prescribed for conditions such as equine asthma, allergic skin disease, hives, inflammatory bowel disease, and certain autoimmune disorders. Corticosteroids can be highly effective in improving a horse’s comfort and quality of life, particularly in cases involving chronic inflammation or severe allergic reactions.

Understanding how prednisolone works, when it is used, and what side effects to watch for can help horse owners make informed decisions alongside their veterinarian. Keep reading to learn more about the uses, risks, dosing considerations, competition regulations, and frequently asked questions surrounding prednisone and prednisolone use in horses.

Prednisolone for Horses

Prednisone and prednisolone are glucocorticoids, medications that exert anti-inflammatory and immunosuppressive effects. Glucocorticoids are also known as corticosteroids. Prednisone is a pro-drug that is converted into the active metabolite prednisolone in the animal’s liver. ^[1]

Despite their benefits, prednisone and prednisolone use comes with risks. Corticosteroid use in horses is often approached cautiously because these medications can increase the risk of complications such as laminitis.

Long-term or high-dose treatment may also suppress the immune system, delay wound healing, or contribute to gastrointestinal and hormonal changes. Because of these concerns, veterinarians typically aim to use the lowest effective dose for the shortest practical duration.

For horses, veterinarians almost exclusively prescribe prednisolone, the active form of the drug. This is because prednisone has poor bioavailability, meaning it is not easily absorbed from the horse’s digestive tract. It also has minimal conversion to prednisolone in the horse’s liver, which means higher doses are required to have the same effect. ^[2]

Available Forms

Prednisolone is available in oral tablets, syrups, and oral solutions. ^[3] Many of the formulations of prednisolone are generic drugs, but brand names include: ^[3]

• Prednis-Tab^®
• Millipred^®
• Orapred^®
• Prelone

These products are labeled for human use, but veterinarians may use them in an off-label manner. Off-label, or extra-label, use refers to uses for conditions or species not listed on the product monograph. This practice is permitted by veterinary prescribing regulations at the veterinarian’s professional discretion.

Drug Class: Glucocorticoids

Glucocorticoids are a class of hormone naturally produced by mammals. The most common glucocorticoid is cortisol, the stress hormone. Glucocorticoid medications, like prednisolone, mimic the activity of cortisol within the body.

There are several different glucocorticoids used in veterinary medicine. Each medication mimics the structure of cortisol, but has a different duration and strength of activity.

Other common glucocorticoids used in equine medicine include: ^[4]

• Dexamethasone
• Isoflupredone
• Triamcinolone
• Beclomethasone
• Fluticasone

Although they have a similar name to anabolic steroids, corticosteroids do not promote muscle growth and cannot be used for this purpose in athletes. In contrast, glucocorticoids often stimulate muscle breakdown and atrophy.

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Mechanism of Action

Cortisol has numerous effects throughout the body, particularly functions related to the “fight or flight” response during times of stress or distress.

Example functions of cortisol include: ^[5]

• Raising blood pressure
• Reducing the function and release of white blood cells
• Inhibiting the inflammatory response
• Reducing tissue healing, including bone remodeling
• Increasing metabolism, including burning fat and protein stores

Although cortisol has numerous effects in the body, veterinarians typically prescribe the medications for anti-inflammatory or immunosuppressive purposes.

Cortisol works at a cellular level to disrupt the “inflammatory cascade”, release of proteins that activate white blood cell activity and other inflammatory functions. ^[4] By giving these medications, veterinarians can help control the pain and tissue damage that occurs during an inflammatory response.

Uses in Horses

Prednisolone is used as an anti-inflammatory and immunosuppressive medication in horses. There are no formulations of prednisolone approved for use in horses, so veterinarians typically use human medications in an off-label manner.

Off-label use of medications is common in veterinary medicine, as drug companies do not test medication for use in every species or for every possible use. When designing a treatment plan, the veterinarian uses previous experience and existing research to determine a dose and time of treatment.

The most common uses of prednisolone in horses are for equine asthma and immune-mediated diseases.

Equine Asthma

Equine asthma is a chronic inflammatory condition affecting the horse’s lower respiratory tract, including the lungs. The condition develops when the airways become hypersensitive to environmental allergens such as dust, mold spores, and hay particles. ^[4]

Exposure to these triggers activates the immune system and leads to inflammation within the lung tissue. Research has shown that glucocorticoids can significantly improve clinical signs in horses with equine asthma by decreasing airway inflammation and improving respiratory function. ^[4]

With that being said, there is also evidence that dexamethasone may be more effective for treatment of asthma than prednisolone. ^[6]

Immunosuppression

Autoimmune and immune-mediated diseases develop when the horse’s immune system mistakenly attacks benign substances it perceives as foreign. In many cases, the immune response targets the horse’s own tissues, leading to inflammation and tissue damage.

Administering high doses of glucocorticoids can downregulate the immune system, reducing tissue damage.

Common immune-mediated diseases in horses include: ^[4][7]

• Vasculitis
• Atopic dermatitis
• Insect bite hypersensitivity
• Pemphigus foliaceus
• Inflammatory bowel syndrome
• Recurrent uveitis
• Immune-mediated thrombocytopenia (low blood platelets)

Administration Routes

Prednisolone is given by mouth as an oral tablet, syrup, or solution. Depending on the palatability of the formulation, the drug may be given in the horse’s grain or syringed into their mouth.

Doses of glucocorticoids can vary depending on the desired purpose of the medication. Lower doses provide minimal immunosuppression and are primarily used as an anti-inflammatory. Higher doses suppress the immune system’s function and are usually used for diseases with an immune-mediated component, such as allergies. ^[3][4][7]

Tapering

Horses receiving prednisolone for longer than 2 weeks should be gradually tapered off the medication rather than having treatment stopped abruptly. ^[3]

High levels of prednisolone slow and eventually stop the body’s natural production of cortisol, particularly when given for a long period. If the medication is discontinued suddenly, the horse may not be able to produce enough cortisol to meet the body’s needs.

This can result in signs of hypoadrenocorticism (low cortisol levels), which may include: ^[8][9]

• Lethargy
• Low blood pressure
• Diarrhea
• Weakness
• Collapse

Storage

Prednisolone tablets should be stored in tightly closed containers below 40ºC (104ºF). Avoid freezing. Oral syrups or solutions may have different storage requirements depending on the manufacturer.

Keep out of reach from children and animals. Always refer to the product label for storage information.

Safety Warnings & Precautions

Glucocorticoids like prednisolone have roles in several body functions. Although veterinarians use these medications for immunosuppressive or anti-inflammatory purposes, their effects on other parts of the body can lead to significant side effects. To avoid or minimize side effects, veterinarians typically use the lowest dose possible for the shortest treatment time possible. ^[3]

Monitoring

Monitoring for prednisolone treatment depends on the reason for using the drug, the dose used, duration of therapy, and the animal’s age.

General monitoring may include: ^[3]

• Response to treatment
• Weight and appetite
• Electrolyte levels in the bloodstream or urine
• Blood glucose
• Gastrointestinal signs such as diarrhea or blood in the feces
• Growth and development in young animals
• Signs of laminitis including heat in the hooves or increased pulses in the lower limbs

Contraindications

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

Glucocorticoids have effects on numerous body systems. Given this, veterinarians must use these drugs carefully in animals with pre-existing conditions.

Common contraindications for prednisolone use include: ^[3]

• Infections: Glucocorticoids can downregulate the immune system. They should not be administered to animals with active bacterial, viral, or fungal infections in most cases. If they must be given simultaneously, most veterinarians combine the glucocorticoid with an antibiotic, antiviral, or antifungal drug to prevent the infection from worsening.
• Hypersensitivity: Animals with pre-existing hypersensitivities may have adverse reactions to glucocorticoids.
• Kidney disease: Animals with kidney disease may have an increased risk of electrolyte loss due to the excessive urination caused by glucocorticoids. They may also have a higher risk of gastrointestinal side effects when given prednisolone.
• Endocrine diseases: Glucocorticoids can disrupt normal hormone pathways. Use with caution in animals with pre-existing endocrine or metabolic disease.
• Osteoporosis: Glucocorticoids can interfere with bone remodeling and remineralization. This may worsen or predispose animals to developing osteoporosis.
• Pregnancy: Administering glucocorticoids during late pregnancy may trigger labor. Prednisolone administration during pregnancy may also increase the risk of congenital abnormalities such as cleft palate.
• Lactation: Prednisolone can pass into mare’s milk, causing increased prednisolone levels in the foal. High levels of prednisolone may inhibit bone growth and affect their natural corticosteroid production. Avoid giving prednisolone to lactating mares when possible.
• Laminitis: There are reports of glucocorticoid administration triggering laminitis episodes in horses. Horses with equine metabolic syndrome, obesity, or other predisposing factors likely have a higher risk. Use these drugs with caution in horses with a history or predisposition to laminitis.

Side Effects

The most frequently reported side effects of glucocorticoid therapy are increased thirst and excessive urination. Some horses may also experience an increased appetite because these drugs can raise metabolic activity. ^[3]

In horses, glucocorticoid use has been associated with laminitis. Although this complication appears to be uncommon in otherwise healthy adult horses, animals with existing risk factors such as obesity or equine metabolic syndrome may be at higher risk. ^[10] Corticosteroids should therefore be used with caution in horses predisposed to laminitis.

Glucocorticoids may also contribute to the development of gastric ulcers. These medications can increase stomach acid production and may weaken the protective mucous barrier lining the stomach, making the tissue more vulnerable to acid injury. ^[3] Careful use is recommended in horses with a current or previous history of gastric ulcers.

With prolonged administration, glucocorticoids can cause a range of additional adverse effects, including: ^[3]

• Increased liver enzyme levels
• A dull, dry, or poor-quality hair coat
• Weight gain
• Loss of muscle mass
• Thinning or calcification of the skin
• Osteoporosis
• Changes in behavior
• Slowed growth in young animals
• Bleeding abnormalities

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Acute Toxicity (Overdose)

A one-time overdose of prednisolone is not expected to cause serious harm in most horses. In the short term, affected horses may show increased thirst and more frequent urination. Horses should be monitored closely for signs of laminitis, such as:

• Lameness
• Standing with the hindquarters shifted backward and the front feet stretched out in front (“sawhorse stance”)
• Increased heat in the hooves
• Stronger or more noticeable digital pulses in the lower limbs

Drug Interactions

Since prednisolone has wide-ranging effects on the horse’s body, it can interact with the function or absorption of several other drugs.

The most important drug interaction with prednisolone is non-steroidal anti-inflammatory drugs (NSAIDs). Both drug classes reduce the production of prostaglandin, a hormone-like compound that stimulates the production of protective mucus and bicarbonate in the stomach.

When prostaglandin production decreases due to corticosteroid and/or NSAID administration, stomach acid can eat away at the stomach lining, producing ulcers. ^[3]

Commonly used NSAIDs in horses include: ^[11]

• Phenylbutazone (“bute”)
• Flunixin meglumine (Banamine^®)
• Firocoxib (Equioxx^®)
• Meloxicam

The immunosuppressive function of glucocorticoids can also affect administration of certain types of vaccines. Modified live vaccines contain a live virus that has been altered in a laboratory to minimize its infection capability. Immunosuppression from glucocorticoid use may allow the virus to replicate more than expected, potentially causing an infection. ^[3]

Glucocorticoids can also interfere with the body’s response to the vaccine, resulting in reduced vaccine efficacy. ^[3]

Since prednisolone is metabolized in the liver, other drugs affecting liver function and metabolism may interact with prednisolone. This can result in altered metabolism of either prednisolone or the other drug administered.

Caution should be used when administering prednisolone alongside: ^[3]

• Azole antifungals, such as ketoconazole or itraconazole
• Cyclophosphamide
• Cyclosporine
• Ephedrine
• Macrolide antibiotics, such as erythromycin
• Mitotane
• Phenobarbital
• Rifampin

Drugs that affect blood electrolyte levels may worsen electrolyte losses from glucocorticoids. Example drugs include: ^[3]

• Amphotericin B
• Desmopressin
• Digoxin
• Potassium-depleting diuretics like furosemide

Other potential interactions include: ^[3]

• Anticholinesterase agents: May trigger profound muscle weakness when given together.
• Antidiabetic agents: May reduce the hypoglycemic effect of SGLT2 inhibitors like velagliflozin.
• Asparaginase: May increase the risk of coagulation disorders or high blood sugar.
• Fluoroquinolone antibiotics: Concurrent use may increase the risk of tendon inflammation and rupture.

Regulatory Status & Legal Considerations

Currently there are no FDA or Health Canada-approved formulations of prednisolone available for horses. Veterinarians use human formulations in an off-label manner when prescribing this drug to horses.

Off-label use is common in veterinary medicine as many drugs have not been approved for every species. However, the drug company that produces the medication may not warranty their product in the event of an adverse reaction.

Status in Competition

Prednisolone is a controlled substance in competitions regulated by the Fédération Equestre Internationale (FEI). This means that the drug can be used outside of competition but is not permitted to be in the horse’s system on competition day.

The FEI also classifies prednisolone as a threshold substance. These are compounds naturally found in the horse’s body that may appear on a drug test. To avoid confusing natural production with medication use, the laboratory sets a threshold value. Testing above this value suggests the horse was administered a drug. The threshold value for prednisolone is 0.01 micrograms per milliliter of urine. ^[12]

Other competitive organizations may permit the use of prednisolone in competition. Always check with your organization prior to administering a drug to your horse.

Frequently Asked Questions

Here are some frequently asked questions about prednisolone for horses:

Summary

Prednisone and prednisolone are corticosteroid medications used in horses to reduce inflammation and suppress abnormal immune responses.

• Prednisolone is generally preferred in equine medicine because horses do not efficiently convert prednisone into its active form
• Prednisolone is commonly used to treat conditions such as equine asthma, allergic skin disease, hives, inflammatory bowel disease, and certain immune-mediated disorders
• Corticosteroid use carries potential risks, including laminitis, immune suppression, delayed wound healing, and increased susceptibility to infection
• Veterinarians typically aim to use the lowest effective dose for the shortest possible duration to reduce the likelihood of side effects
• Competition rules regarding prednisolone vary between organizations, so owners and riders should always verify medication regulations and withdrawal times before competing