Fexofenadine (Allegra®, Telfast®) for Dogs and Cats

Overview of Fexofenadine for Canines and Felines

• Fexofenadine, commonly known as Allegra® or Telfast®, is a second generation antihistamine drug that may be used for dogs and cats to control itching and other signs related to allergic conditions.
• Fexofenadine is considered less sedating than other antihistamines.
• WARNING: If you use Allegra®, only use the product that indicates the active ingredient is Fexofenadine. Do not use the product that includes the active ingredients of Fexofenadine AND pseudoephedrine such as Allegra-D®. Pseudoephedrine (Allegra-D®) can be toxic to pets. Also – the human fexofenadine oral suspension contains xylitol (may be toxic in dogs). To learn more – go to Xylitol Toxicity in Dogs.
• The use of Fexofenadine in dogs and cats has been limited. Much of the information about how Fexofenadine works in dogs and cats, as well as its side effects, has largely been extrapolated from human literature and information about the other antihistamines more commonly used in dogs.
• Histamine is a chemical that is released in the body in response to an inflammation or allergy. This chemical travels throughout the body searching for specific histamine receptors (targets on cells). Once attached to the receptors, histamine will cause swelling, itchiness, and other symptoms associated with an allergic response.
• There are two types of histamine receptors: H1 and H2. H1 receptors affect small blood vessels and smooth muscles. When histamine attaches to the H1 receptors, the small blood vessels dilate, and fluid begins to leak out. This results in tissue swelling and itchiness. In addition, the smooth muscles lining the small airways constrict, causing tightness and some breathing difficulty. H2 receptors affect heart rate and stomach acid secretions. When histamine attaches to H2 receptors, the heart rate increases and stomach acid secretions are increased, potentially increasing the risk of developing ulcers.
• Drugs that block the effects of histamine are called antihistamines. There are a number of drugs demonstrating antihistamine effects; some are useful in allergies and others for preventing excessive stomach acid. The effects of the antihistamine depend on whether it binds with the H1 receptors or H2 receptors. There are few drugs that affect both types of receptors.
• Fexofenadine is one type of antihistamine that inhibits the action of histamine, particularly its effect on H1 receptors. This results in a reduction or prevention of swelling and itchiness. Fexofenadine has little to no effect on heart rate or stomach acid secretions.
• Fexofenadine is available over the counter but should not be administered unless under the supervision and guidance of a veterinarian.
• This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

Brand Names and Other Names

• This drug is registered for use in humans only.
  Human formulations: Allegra®, Telfast®, and various generic preparations
  Veterinary formulations: None

Uses of Fexofenadine

• Fexofenadine is used primarily to treat allergic conditions including atopic dermatitis and allergic rhinitis. It can help control itching in some pets and is best started before the itching is worst and used consistently.
• Antihistamines generally work best if started before exposure to the allergen and used regularly.

Precautions and Side Effects

• While generally safe and effective when prescribed by a veterinarian, Fexofenadine can cause side effects in some animals.
• Fexofenadine should not be used in animals with a known hypersensitivity or allergy to the drug.
• Fexofenadine is not approved for use in pregnant or nursing dogs or cats.
• Fexofenadine should be used with caution in animals with kidney disease.
• Fexofenadine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with
  Fexofenadine. Such drugs include antacids, erythromycin, ketoconazole, and ivermectin.
• The most common adverse effects of Fexofenadine are sedation, lethargy, dry mouth, vomiting, and possible diarrhea.

How Fexofenadine Is Supplied

• Fexofenadine is available in tablets, oral dispersible tablets and as an oral solution.
• Fexofenadine oral tablet sizes include 60 and 180 mg.
• Fexofenadine is available as an oral “dispersible tablet” in 30 mg size. Note: The orally disintegrating tablet is made to dissolve on the tongue of humans which makes its use in dogs and cats difficult. Also, some oral disintegrating tablets may contain xylitol which can be toxic to pets. For more information, go to Xylitol Toxicity.
• Fexofenadine is available as an oral suspension: 30 mg/5 mL (6 mg/mL). This product contains xylitol – DO NOT USE IN DOGS.
• There is also fexofenadine/pseudoephedrine combination products available (Allegra D®). DO NOT USE ALLEGRA D IN PETS.
• Fexofenadine is also available an oral suspension that contains xylitol (NOTE: Xylitol may be toxic in dogs). The human oral suspension is not recommended for use in pets.

Dosing Information

• Medication should never be administered without first consulting your veterinarian. This drug has not been well studied in dogs and the oral solution may contain xylitol, a known canine toxin.
• In dogs, Fexofenadine is dosed at 1 mg per pound to 2.5 mg per pound of body weight (2 to 5 mg/kg) every 12 to 24 hours. One study suggested higher dosages once daily has been effective in some dogs (9 mg per pound). Another way that
  Fexofenadine is dosed in dogs is by the total dose. Because of the pill sizes, dosages are often rounded to the closest tablet size. For example, small dogs often receive a total dose of 15 mg and large dogs a total dose of 30 mg.
• In cats, Fexofenadine has not been studied, and no well-established doses are published. Some reports suggest a TOTAL dose of 10 to 15 mg per cat orally once daily.
• Can be given with food or without. For pets that experience gastrointestinal upset, you may give Fexofenadine with food.
• The duration of administration depends on the condition being treated, response to the medication, and the development of any adverse effects. A minimum trial of two weeks is often recommended to determine if Fexofenadine is effective for a pet.
• Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse.