Cetirizine for dogs

Cetirizine HCl is an over-the-counter antihistamine that relieves seasonal allergy symptoms such as sneezing and runny nose in people. Veterinarians use cetirizine to treat dogs with itchy skin due to atopic dermatitis or allergies. While it is safe for dogs to take, it’s one of the least effective antihistamines at providing itch relief for dogs. On the other hand, side effects are mild. Cetirizine is less likely to cause drowsiness or sleepiness in dogs than early-generation antihistamines such as Benadryl (diphenhydramine). The FDA has not approved cetirizine for use in animals, so only give your dog cetirizine under the direction of a veterinarian.

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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, extra-label use of antihistamines like cetirizine includes any itch involving histamines, such as allergic reactions, insect bites, or hives. 

Atopic dermatitis and allergic pruritus

Atopic dermatitis is a type of eczema in which a combination of environmental factors and the immune system causes regular flare-ups of itching, swelling, redness, and other skin problems. Contact allergies can produce similar reactions. 

In humans, the itching of atopic dermatitis and contact allergies are caused by histamines, chemicals that activate the nerves that produce the itching sensation. Histamine also increases blood flow to the area, causing swelling and redness. 

Cetirizine works by attaching to histamine receptors on skin and skin nerve cells so that histamines don’t trigger swelling and itching. Unfortunately, itching and swelling in a dog are not as dependent on histamines and H1 receptors as in humans. Antihistamines can help, but they’re not as powerful in providing symptom relief in dogs. Some don’t work at all at relieving canine itch.

Among the antihistamines used in dogs, cetirizine is one of the least effective. It does work, but one placebo-controlled study showed that only about 18% of dogs get significant itch relief from oral cetirizine. Two studies showed that cetirizine was no better than taking an inert placebo without any active ingredient. Other antihistamines have produced better results in clinical studies. Some of those are first-generation antihistamines, which are more likely to cause drowsiness and other side effects on the central nervous system.

One 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.

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Is cetirizine safe for dogs?

Cetirizine is safe for dogs but may not be the best anti-itch treatment. Side effects are mild, and no severe side effects have been reported. 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.

Products containing cetirizine and the decongestant pseudoephedrine like Zyrtec-D Allergy & Congestion should never be given to dogs. Pseudoephedrine could poison and harm the dog. 

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 people.

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, over-the-counter 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 dosage for dogs

There are several published cetirizine dosages for dogs, but the Merck Veterinary Manual suggests a once-daily or twice-daily dose of 1 mg/kg (0.45 mg/lb). Another alternative is a once- or twice-daily dose of 10–20 mg tablets, making it easier to dose the dog with over-the-counter cetirizine tablets. 

There are no veterinary formulations of cetirizine. 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. Compounding pharmacies are another source. 

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Can dogs overdose on cetirizine?

There is no information about cetirizine overdoses in dogs. 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 the 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. 

However, cetirizine isn’t very effective. Talk to a veterinarian if the drug doesn’t work after two weeks of daily dosing. 

How to give your dog cetirizine

Cetirizine can be given to a dog as a tablet or syrup. 

• Do not give your dog cetirizine except under the direction of a veterinarian.
• Follow all the veterinarian’s instructions. 
• Cetirizine can be given with or without food. If the dog is vomiting up the dose, start giving doses with food.
• If you’re giving the dog cetirizine oral syrup, use the measuring device with the medicine to measure out doses. 
• 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 that missed dose and give the next dose on schedule. 
  • For once-daily dosing, give the dose when reminded if it’s the same day for once-daily dosing. 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 this drug is discontinued.

Cetirizine alternatives for dogs

In general, antihistamines are variable in their effectiveness in helping relieve itching in dogs with atopic dermatitis or other reasons. According to clinical studies, the most effective antihistamines for canine itchy skin are:

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

Antihistamines are normally not the first choice for the treatment of canine atopic dermatitis, but 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)

Summary

Cetirizine is a low-priced antihistamine used in dogs to prevent or relieve itchiness due to atopic dermatitis or other problems. 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.