Skin allergies in horses are usually caused as a result of physical contact with irritating substances or via the ingestion of a food that causes a reaction in the horse’s skin. The symptoms that develop may be an immediate response to an allergen, or they may develop over time.¹ The resulting itching and rashes can be very irritating to the horse.

A horse may develop an allergic reaction to one or more substances or foods with no apparent cause. While an allergic reaction represents the horse’s body protecting itself from something harmful, a given substance or food may elicit this reaction even if it is not harmful. In either case, the resulting symptoms will need to be addressed.

There is no timeframe or age relating to a horse developing a skin allergy; they can develop early or late in a horse’s life.¹While there is no treatment that can cure allergies, they can be managed with the help of a veterinarian. In some cases, a modified dietary regimen can bring relief. Proper diagnosis and treatment can keep affected horses comfortable by mitigating the symptoms.

Hives (urticaria) in the horse are “itchy eruptions of localized swelling in the dermis.”² These can develop and disappear suddenly. While the most common causes of hives in horses are insect bites or stings, other potential causes include vasculitis, allergies and certain medications. Hives may appear within a few minutes or hours of exposure to the causative agent. 

Hives often disappear as rapidly, within a few hours of exposure to an irritant or allergen, and are seldom directly harmful to the horse. In the case of chronic hives, the horse owner or manager should consider environmental allergens, and take steps to prevent repeated exposure if possible. “Sensitive animals, particularly purebred horses, also may exhibit dermographism, a phenomenon in which rubbing or whipping produces hive-like inflammations. These are of no medical significance.”²

Symptoms of skin allergies in the horse can include:

• Itchy skin
• Lesions
• Hives
• Hair loss
• Self-trauma of skin
• Severe skin damage
• Secondary skin infection
• Respiratory distress³

Tripelennamine HCL for Horses

Tripelennamine hydrochloride is an injectable antihistamine that is FDA-approved for use in horses and cattle.⁴ It is a white, crystalline material that is stable and readily soluble in water. It is derived from pyridine and ethylemediamine and used in the form of a crystaline citrate as an intramuscular injection.¹ This medication competes with histamines for uptake at the histamine receptors on sensitive cells in the respiratory tract, intestines, blood vessels, and skin. Tripelennamine can be used with corticosteroids, allowing use of a lower dose of corticosteroids prescribed for the allergic reaction.

Labeled for treating “conditions in which antihistaminic therapy may be expected to alleviate some signs of disease,”⁴tripelennamine is a first-generation antihistamine that competitively inhibits histamine at H1 receptor sites. It does not prevent the release of histamine, but can prevent histamine’s action. Tripelennamine has moderate sedative activity and minimal anticholinergic activity compared to other first-generation antihistamines.

Tripelennamine is contraindicated in patients that are hypersensitive to it, and IV administration is contraindicated in horses. Other possible adverse effects include CNS depression, ataxia, and GI disturbances; CNS stimulation lasting up to 20 minutes has been noted in horses after administration of label-recommended dosages.⁴

Warming the solution to near body temperature before injecting is recommended, as well as giving IM injections into one of the large muscle groups.

Dosages of tripelennamine for horses are as follows (adapted from Plumb’s Veterinary Drugs):

Antihistamine (label dosage; FDA-approved): 1.1 mg/kg IM every 6 to 12 hours as needed. 

NOTE: Do NOT administer IV to horses.

Where to buy Tripelennamine

Tripelennamine is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. TRIPELENNAMINE HCL 20 MG/ML, INJECTABLE SOLUTION, 100ML by NexGen Pharmaceuticals is indicated for conditions in which antihistaminic therapy may be expected to alleviate skin allergies in the horse. 

This drug carries several potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹equimed.com.

²wagwalking.com.

³Merck Veterinary Manual.

⁴Plumb’s Veterinary Drugs.