Cetirizine (Zyrtec®) for Dogs and Cats

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Overview of Cetirizine (Zyrtec®) for Dogs and Cats

  • Cetirizine, commonly known by the brand name Zyrtec®, is a type of anti-histamine commonly recommended for dogs with itching. It can also be used in cats.
  • Histamine is a chemical that is released in the body in response to 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, 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.
  • Cetirizine is one type of antihistamine referred to as a second generation h1 receptor blocker that inhibits the action of histamine, particularly its effect on H1 receptors. This results in a reduction or prevention of swelling and itchiness. Cetirizine has little to no effect on heart rate or stomach acid secretions.
  • Cetirizine 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 of Cetirizine

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

Uses of Cetirizine for Dogs and Cats

Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, cetirizine can cause side effects in some animals.
  • Cetirizine should not be used in animals with known hypersensitivity or allergy to the drug.
  • Cetirizine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with cetirizine. Such drugs include central nervous system depressants.
  • The most common adverse effects of cetirizine are sedation, lethargy, vomiting, drooling (hypersalivation), and lack of appetite.

How Cetirizine Is Supplied

  • Cetirizine is available in 5 mg and 10 mg tablets.
  • Cetirizine is also available in 5 mg and 10 mg chewable grape flavored tablets.
  • It is also available as oral syrup in the concentration of 1 mg/ml. This can be stored at room temperature or in the refrigerator.

Dosing Information of Cetirizine for Dogs and Cats

  • Medication should never be administered without first consulting your veterinarian.
  • Cetirizine is dosed in dogs at 0.5 mg per pound (1 mg/kg) orally once to twice daily.
  • In cats, cetirizine is dosed at a total dose of 5 mg per cat once daily.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. 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.


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