Skip to main content
Pets

Zyrtec for cats: Dosage and safety

Zyrtec treats itchy skin in cats
SingleCare logo
By | Jun. 17, 2024 Medically reviewed by Emma Ryan, DVM
A grey cat sitting: Zyrtec for cats

Key takeaways

  • Zyrtec is used to treat itchy skin and chronic sinus and nasal inflammation in cats.

  • The standard Zyrtec dosage for cats is 2.5–5 mg once daily.

  • The most common side effect of Zyrtec in cats is sleepiness.

  • Do not give Zyrtec to cats allergic to cetirizine or hydroxyzine.

In this article:

Zyrtec is a brand-name allergy medication that can be purchased over the counter. The active ingredient in Zyrtec is cetirizine, a non-drowsy antihistamine. People buy Zyrtec to treat seasonal allergy symptoms such as sneezing, runny nose, and watery eyes, but antihistamines aren’t as effective at relieving allergy symptoms in pets. Veterinarians may use it to relieve itchy skin in cats and dogs. Less commonly, veterinarians may use it in cats to treat chronic sinus and nasal inflammation when other drugs don’t work. Although side effects are minimal, its use in animals is “off-label.”

RELATED: Save up to 80% on Zyrtec

What is Zyrtec used for in cats?

Veterinarians use Zyrtec or generic cetirizine in cats to treat itchy skin (pruritus) due to skin allergies, hives, or insect bites. However, antihistamines are not very effective at treating pruritus in cats, so they’re not usually the first or best choice. Cetirizine is a suggested but unproven therapy to treat chronic swollen sinuses and nasal passages when other drugs don’t work. 

Itchy skin

As pet parents know, itchy skin is as common in pets as in humans. All the same causes, such as allergic reactions, hives, food allergies, flea bites, and insect bites, are to blame. Feline atopic skin syndrome (FASS), an itchy skin condition related to environmental allergies, is the most common feline skin condition veterinarians treat.

In people, persistently itchy skin is often due to histamines. These chemicals activate the immune system and cause skin to swell and grow red. They also activate the nerves that cause itching sensations. Zyrtec works by attaching to histamine receptors on skin and nerve cells so that histamines can’t provoke swelling and itching. 

That’s how histamines and antihistamines work in humans. Unfortunately, histamines don’t affect cats as powerfully as they affect people. So Zyrtec and other antihistamines have less of an effect on itchiness in cats than they do in humans.  

The standard treatment for itchy skin in cats is corticosteroids such as prednisolone or dexamethasone. Because corticosteroids can have pronounced side effects, veterinarians usually use antihistamines as an add-on treatment so they can reduce the corticosteroid dose. 

RELATED: Stop the itch: How to treat allergies in cats and dogs 

Chronic rhinosinusitis (CRS)

Rhinosinusitis is swelling of the nasal passages (rhinitis) and sinuses (sinusitis). It is a common symptom of allergies, viral infections, bacterial infections, and fungal infections. Sometimes, the swelling doesn’t clear up but continues for a month or longer. That’s when it’s considered chronic rhinosinusitis.

Veterinarians are unsure what causes chronic rhinosinusitis in cats, but it typically follows an infection. Over time, the condition could damage tissues in the nose and sinuses, depriving the cat of an important filtration system that protects the lungs from foreign debris and microorganisms. 

Veterinarians don’t have sure-fire treatments for chronic rhinosinusitis in cats. The condition may not be curable but can be managed. The standard and most successful treatment involves antibiotics. If those don’t work, unproven or marginally successful treatments include corticosteroids, nasal lavage, humidifiers, immune suppressants, and second-generation antihistamines such as Zyrtec. 

Is Zyrtec safe for cats?

Zyrtec is safe for cats but may not be very effective at relieving itchiness. Cats with hypersensitivity to cetirizine or a similar drug called hydroxyzine cannot safely be given Zyrtec. 

Never give a cat Zyrtec-D, a drug that combines cetirizine with pseudoephedrine, a decongestant. Any over-the-counter medication that contains pseudoephedrine or phenylephrine will endanger your pet. Even a small dose might be toxic, causing high blood pressure and a fast heart rate.

Side effects of Zyrtec in cats

Zyrtec side effects in cats are uncommon and not well-documented. The most likely side effect is sleepiness. Side effects in humans also include:

  • Vomiting
  • Dry mouth
  • Fatigue

No serious side effects have been reported in pets.

Interactions of Zyrtec with other pet meds

Do not give a cat Zyrtec until talking to a veterinarian. Tell the veterinarian about all the drugs, remedies, vitamins, and supplements the cat receives. 

Zyrtec has few drug interactions. The most likely side effect is drowsiness, so a veterinarian may be cautious about combining Zyrtec with drugs that cause sedation, including: 

Allergy skin tests may not work in cats taking Zyrtec. Any antihistamine will have to be stopped at least one week before an allergy skin test.

Zyrtec dosage for cats

Several cetirizine dosages are recommended for cats, so dosages may vary between veterinary professionals. Plumb’s Veterinary Drug Manual suggests the following dosages:

  • For itchy skin: 2.5–5 mg once per day
  • For non-responsive chronic rhinosinusitis: 5 mg once or twice per day

The American Animal Hospital Association recommends a dosage of 5–10 mg per day for itchy skin. The Merck Veterinary Manual suggests a dose of 1 mg/kg or 5 mg once or twice daily.

Can cats overdose on Zyrtec?

Do not give a cat too much Zyrtec. If the cat is given too much Zyrtec, call a veterinarian for advice. If a veterinarian cannot be reached, consider taking the cat to an emergency animal hospital. The most likely effects of high doses of cetirizine might be slowness, sleepiness, or hyperactivity.

If a cat is given Zyrtec-D, a dose or overdose can cause serious or even life-threatening problems. Take the cat to an emergency veterinary hospital. Symptoms of a pseudoephedrine overdose in a pet include hyperactivity, agitation, restlessness, dilated pupils, vomiting, fast heartbeats, and possibly seizures.

Can I give my cat Zyrtec every day?

When prescribed by a veterinarian, Zyrtec is safe to give a cat daily, provided the vet’s instructions are followed. It may not be effective, but it could help reduce the dose of any corticosteroid prescribed to relieve itchiness.

How to give your cat Zyrtec

Zyrtec comes in several formulations, including tablets, capsules, chewable tablets, orally disintegrating tablets and liquid. Most formulations usually do not come in dosage strengths appropriate for a cat other than Children’s Zyrtec Allergy syrup or 2.5 mg chewable tablets. The veterinarian may need to supply cetirizine specially formulated as a tablet or oral solution from a compounding pharmacy.

To ensure safety and effectiveness, here are a few pointers:

  • Do not give a cat Zyrtec or generic cetirizine except under the direction of a veterinarian.
  • Follow all the veterinarian’s instructions. 
  • Cats can take a cetirizine dose with or without food. If the dose makes the cat vomit or feel sick, try giving the dose with food.
  • If you’re not experienced at giving pills to a cat, ask a veterinary professional to demonstrate the proper technique. The veterinarian may suggest a pill plunger, but get a demonstration before using one.
  • If you give the cat an oral syrup or solution, use the measuring device that comes with the medicine to measure out doses. The bottle does not need to be shaken before measuring out a dose.
  • Ask the veterinarian if it’s possible to use Zyrtec chewable tablets. Many cat medications come as chewable tablets, but Children’s Zyrtec Allergy is flavored to appeal to children. The cat may refuse it. 
  • What to do in case a dose is missed will depend on the dosing schedule. 
    • For twice-daily dosing, if a dose is missed, skip it and give the next dose on schedule. 
    • For once-daily dosing, give the dose when remembered if it’s the same day. If it’s the next day, give the next day’s dose as scheduled. 
    • Do not give two doses to make up for a missed dose.
  • There is no need to taper the dose when Zyrtec is discontinued.

Zyrtec alternatives for cats

Antihistamines are ineffective on their own at treating itchy skin or chronic rhinosinusitis in cats. 

Instead, the preferred treatments for treating itchy skin in cats are:

  • Corticosteroids such as prednisolone
  • Immune suppressants such as cyclosporine or oclacitinib
  • Allergen-specific immunotherapy
  • Essential fatty acids
  • Maropitant
  • Gabapentin

Zyrtec may be used to help lower the corticosteroid dose and relieve the cat of corticosteroid side effects. If the cat can’t take cetirizine, alternative antihistamine therapies include: 

Antibiotics are the preferred treatment for chronic rhinosinusitis. Other treatments, such as antihistamines, are unproven or only sometimes successful.

Summary

Zyrtec and its generic cetirizine are safe for cats but ineffective at treating itchy skin or chronic nasal and sinus swelling. Veterinary professionals are more likely to use Zyrtec with corticosteroids to treat itchy skin to reduce the corticosteroid dose. Zyrtec with pseudoephedrine can cause serious and life-threatening problems in a cat, so avoid giving Zyrtec-D or any cetirizine product containing pseudoephedrine to a cat.

Sources