By Rania Gollakner, BS, DVM, MPH

What is cetirizine?

Cetirizine (Zyrtec®, Reactine®) is an antihistamine used to treat and prevent pruritus (itching) associated with atopic dermatitis, urticaria (hives), and insect bite reactions in cats and dogs.

Its use is in cats and dogs is ‘off-label’. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully.

How is cetirizine given?

Cetirizine is given by mouth in the form of a tablet or syrup. It may be given with or without food. If your pet seems unwell or vomits after receiving the medication, try giving it with a small amount of food. Measure liquid forms carefully.

This medication will take effect in one to two hours and improvement of your pet's symptoms should follow.

What if I miss giving my pet the medication?

If your pet is receiving cetirizine twice a day and you miss a dose, give the next dose when it is time to do so.

If you are giving the medication once a day, give it when you remember and continue giving the medication at the regular time. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Cetirizine does not typically cause any side effects. Vomiting and increased salivation have been observed in some dogs. At high doses, sleepiness has been reported in small dogs and cats. Any side effects that are severe or worsen should be reported to your veterinarian.

This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

DO NOT use the combination product containing pseudoephedrine in dogs and cats. Cetirizine should not be used in patients that have a hypersensitivity to it or hydroxyzine (Atarax®, Vistaril®).

You should use cetirizine with caution in pets:

• with a seizure disorder
• with difficulties urinating or appear to be constipated
• with thyroid problems, prostatic enlargement, or with heart, kidney, or liver disease
• who are senior
• with glaucoma
• who are working dogs, as they may become sleepy and unable to perform their duties
• who are pregnant and nursing mothers

Are there any drug interactions I should be aware of?

Certain drugs are known to interact with cetirizine, including digoxin (Lanoxin®, Cardoxin®) and central nervous system depressants, such as diazepam (Valium) and alprazolam (Xanax®, Niravam®). Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

This medication may interact with intradermal allergy testing and should be discontinued two weeks before testing.

Is there any monitoring that needs to be done with this medication?

No specific monitoring is necessary for cetirizine. Your veterinarian may wish to examine your pet to check on the effectiveness of the drug. Monitor for side effects.

How do I store cetirizine?

Cetirizine tablets should be stored in the original container at room temperature, between 20-25°C (68-77°F). Oral syrups should be stored at room temperature or in the refrigerator.

What should I do in case of an emergency?

While the risk of a cetirizine overdose is low, overdoses of cetirizine products also containing pseudoephedrine can be serious. If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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