Cetirizine for dogs: Dosage and safety of generic Zyrtec

In this article:

• What is cetirizine used for in dogs?
• Zyrtec (cetirizine) dosage for dogs
• Cetirizine dosing chart for dogs
• How to give your dog Zyrtec (cetirizine)
• What to do if you miss a dose
• Side effects
• Interactions with other pet meds
• Cetirizine alternatives for dogs
• FAQs

In this article

• What is cetirizine used for in dogs?
• Zyrtec (cetirizine) dosage for dogs
• Cetirizine dosing chart for dogs
• How to give your dog Zyrtec (cetirizine)
• What to do if you miss a dose
• Side effects
• Interactions with other pet meds
• Cetirizine alternatives for dogs
• FAQs

Cetirizine is an over-the-counter (OTC) antihistamine that relieves seasonal allergy symptoms such as sneezing and a runny nose in people. It is a generic drug that’s available as brand-name Zyrtec. Even though the Food and Drug Administration (FDA) hasn’t approved cetirizine for use in animals, veterinarians may prescribe it to treat dogs with itchy skin due to atopic dermatitis or allergies. It’s important to only give your dog cetirizine under the direction of a veterinarian, but here’s what you can expect.

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What is cetirizine used for in dogs?

Veterinarians may use cetirizine to treat itchy skin (pruritus) in dogs due to atopic dermatitis. However, it may also be used to treat any itch involving histamines, such as allergic reactions, insect bites, or hives. 

A benefit of antihistamines like cetirizine is that they can be used with oral or topical corticosteroids, the most effective treatment for canine itchy skin. The combination works well and allows for lower steroid doses, helping to reduce the side effects of corticosteroid treatment.

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

Zyrtec (cetirizine) dosage for dogs

There are no veterinary formulations of cetirizine, so there is no “dog Zyrtec dosing chart,” per se. However, the Merck Veterinary Manual suggests a once- or twice-daily dose of 10–20 mg tablets. Alternatively, your veterinarian may prescribe a once-daily or twice-daily dose by weight, which is usually 1 mg/kg (0.45 mg/lb).  

Dog Zyrtec dosing chart by weight
Forms	<5 lbs	5–10 lbs	11–20 lbs	21–50 lbs	50–100 lbs
5 mg or 10 mg tablet of Zyrtec or cetirizine	½ of a 5 mg tablet	1, 5 mg tablet	1, 10 mg tablet	1,10 mg tablet twice a day	2, 10 mg tablets twice a day

*This table is for general guidance only. Always follow your veterinarian’s instructions when administering medication to pets. 

Pet parents must rely on human products such as tablets, chews, or oral syrup. Tablets can be purchased over the counter, but cetirizine oral syrup can only be purchased with a prescription from your veterinarian. You can take the prescription to your regular pharmacy or to a compounding pharmacy, which can create flavored medications that picky dogs are more willing to take.

How to give your dog Zyrtec (cetirizine)

You can provide liquid or tablet forms of cetirizine to your dog. Although Zyrtec and cetirizine are generally safe for dogs, some products, such as Zyrtec-D Allergy & Congestion, combine cetirizine and the decongestant pseudoephedrine. Those medications should never be given to dogs, as pseudoephedrine could poison and harm the dog. 

Follow all your veterinarian’s instructions, which may include: 

• If you’re giving the dog cetirizine oral syrup, use the measuring device with the medicine to measure out doses. If you’re instructed to administer half of a tablet, use a pill cutter to ensure accurate dosing.
• Provide cetirizine with or without food. If the dog is vomiting up the dose, start giving doses with food. Consider hiding the tablet in a pill pocket or a favorite treat if they refuse their dose.

What to do if you miss a dose of cetirizine for your dog

If your dog misses a dose of cetirizine, the next steps will depend on the dosing schedule: 

• For once-daily dosing, give the dose as soon as you remember. 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.
• For twice-daily dosing, if a dose is missed, skip that missed dose and give the next dose on schedule. 

There is no need to taper the dose when this drug is discontinued.

RELATED: Cetirizine dosage, forms, and strengths

Side effects of cetirizine in dogs

According to “Plumb’s Veterinary Drug Manual,” the most common side effects of cetirizine in dogs are:

• Vomiting
• Hypersalivation
• Drowsiness (in smaller dogs)

Drowsiness, fatigue, and dry mouth are the most commonly reported side effects of oral cetirizine in humans.

No serious side effects have been reported in dogs given cetirizine.

Interactions of cetirizine with other pet meds

Before giving a dog cetirizine, tell the prescribing veterinarian about all the drugs, OTC remedies, vitamins, and supplements the dog is being given. Cetirizine has very few drug interactions, but veterinarians may still use it with caution in dogs who are also taking drugs that cause drowsiness or sleepiness, called central nervous system depressants. These include:

• Opioids
• Benzodiazepines
• Cannabinoids (CBD)

Cetirizine might worsen the sedative effects of these drugs. 

Cetirizine will interfere with any allergy skin tests, so the medication should be stopped at least one week before any such test.

Cetirizine alternatives for dogs

While cetirizine is safe for dogs, it’s one of the least effective antihistamines for relieving itch. In humans, cetirizine works by attaching to histamine receptors on skin and skin nerve cells so that histamines don’t trigger swelling and itching. But, itching and swelling in a dog are not as dependent on histamines and H1 receptors as in humans. One placebo-controlled study published in The Canadian Veterinary Journal showed that only about 18% of dogs get significant itch relief from oral cetirizine. 

Although other antihistamines have produced better results than cetirizine in clinical studies, some of those are first-generation antihistamines, which are more likely to cause drowsiness and other central nervous system side effects. According to clinical studies, the most effective antihistamines for canine itchy skin are:

• Hydroxyzine
• Fexofenadine
• Trimeprazine
• Chlorpheniramine
• Promethazine
• Clemastine
• Cyproheptadine
• Diphenhydramine

A benefit of antihistamines like cetirizine is that they can be used along with other, more effective drugs. Depending on the severity of the dog’s itch, the most effective treatments for canine itchy skin are: 

• Oral corticosteroids such as prednisolone 
• Topical corticosteroids such as hydrocortisone or triamcinolone
• The immune suppressants cyclosporine, Apoquel (oclacitinib), or Cytopoint (lokivetmab)

Bottom line

Cetirizine is a generic form of Zyrtec. It is a low-cost antihistamine used in dogs to prevent or relieve itchiness associated with atopic dermatitis or other conditions. It’s not as effective as other antihistamines, but it has mild side effects. Veterinarians primarily use it as an add-on treatment to other therapies such as steroids. Be warned that many cetirizine products also contain pseudoephedrine, a medicine that can be toxic to dogs, so make sure the dog is being given cetirizine-only products.

Frequently asked questions about Zyrtec (cetirizine)

Is cetirizine safe for dogs?

Cetirizine is safe for dogs when administered under a veterinarian’s guidance. Because cetirizine is a second-generation antihistamine that does not cross the blood-brain barrier, it’s less likely to cause side effects on the nervous system, such as drowsiness, dizziness, and dry mouth. Cetirizine should never be given to dogs with hypersensitivity to cetirizine or hydroxyzine. 

Can dogs overdose on cetirizine?

There is no information about cetirizine overdoses in dogs, but in humans, cetirizine overdoses have occurred mainly in children who consume too much medicine when it’s not stored properly. In those cases, the overdoses have caused drowsiness and sedation and have usually resolved without serious incident. Call your veterinarian or animal poison control center for advice if a dog is given too much cetirizine. If the dog consumes a cetirizine product containing pseudoephedrine, immediately take the dog to a veterinarian or veterinary hospital.

Can I give my dog cetirizine every day?

Dogs can be given cetirizine every day. It may be prescribed as a long-term treatment to prevent itchy skin caused by atopic dermatitis. Side effects are minimal, and there are no known side effects from long-term use. Talk to a veterinarian if cetirizine doesn’t work after two weeks of daily dosing.