Cetirizine

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. It may also be used for respiratory allergy symptoms.

Its use in cats and dogs is off label (extra label). Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How is cetirizine given?

• Cetirizine is given by mouth in the form of a tablet or syrup.
• Measure liquid forms carefully.
• Cetirizine 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. 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 are giving cetirizine twice a day and you miss a dose, give the next dose when it is time to do so.
• If you are giving cetirizine once a day and you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects?

Cetirizine may cause the following side effects:

• Vomiting and increased salivation (rare)
• Sleepiness in small dogs and cats (at high doses)

Any side effects that are severe or worsen should be reported to your veterinarian. Drug sensitivities can develop over time, with repeated exposure. Your pet may have no reaction after the first few doses but may develop a sensitivity later. It is important to watch for signs of an allergic reaction over the entire course of treatment.  

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately.  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 cetirizine and pseudoephedrine combination product in:

• Dogs and cats

DO NOT USE cetirizine in:

• Pets with a hypersensitivity to cetirizine or hydroxyzine (Atarax®, Vistaril®).

USE WITH CAUTION in pets that:

• Have a seizure disorder
• Have difficulties urinating or appear to be constipated
• Have thyroid problems or prostatic enlargement
• Have heart, kidney, or liver disease
• Have glaucoma
• Are senior
• Are working dogs (they may become sleepy and unable to perform their duties)
• Are pregnant or nursing

Are there any drug interactions I should be aware of?

Several medications should be used with caution when given with cetirizine, including:

• Central nervous system depressants, such as diazepam (Valium®) and alprazolam (Xanax®, Niravam®)

This medication may interact with intradermal allergy testing and should be discontinued two weeks before testing. Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any treatment.

Is any monitoring needed with this medication?

• No specific monitoring is necessary for cetirizine.
• Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.
• At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian.

How do I store cetirizine?

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

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. Be prepared to provide information about the product and your pet's weight and symptoms.