Pet Medication 101: Zyrtec

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Pet Medication 101: Zyrtec

It’s important to understand a medication’s uses and side effects before giving it to your pet. This medication info sheet is meant to give you a good understanding of what Zyrtec (cetirizine) is used for, how it works, and potential side effects in cats and dogs. Always consult a veterinarian before giving your pet any medication.

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1. Drug Name:


2. Common Names or Brand Names:

Zyrtec, Aller-Tec, Alleroff, Reactine

3. How Dispensed:


4. Forms:

5mg and 10mg tablets, 10mg disintegrating tablets, 10mg chewable tablets, 5mg/5mL oral syrup

5. Drug Type/Class:

antihistamine, piperidine class

6. Uses for Cats and/or Dogs:

vaccine reactions, itchy skin, blood transfusion reactions, bee stings, insect bites, snake bites, mast cell tumor inflammation

7. How it Works:

Cetirizine blocks H1 cellular receptors and prevents their activation by histamine. Histamine is an inflammatory biochemical that causes skin redness, tissue swelling, and itching - many of the symptoms that we associate with an allergic reaction.

Histamine is released from mast cells and attaches to other cells that have histamine receptors on their surfaces. There are more types of histamine receptors than just H1 receptors, and histamine is not always the primary mediator of inflammation in pets. This means that antihistamine therapy is not always as reliable in dogs and cats as it is in people.

Cetirizine does not cross the blood-brain barrier, and therefore does not cause drowsiness like traditional antihistamines.

8. Side Effects and/or Signs of Overdose:

Vomiting, increased salivation, and urine retention have been reported in dogs. At high doses, sleepiness has been reported in small dogs and cats.

Signs of overdose include hyperactivity or depression, depending on how much was ingested.

9. Drug Interactions:

CNS depressants (e.g. diazepam, alprazolam) and digoxin have been known to interact with cetirizine and should not be used together. Cetirizine should not be used with tranquilizing medications as this can increase its sedating properties. Theophylline reduces the breakdown of cetirizine and can increase blood levels.

10. Cautionary Statements:

  • Never give your pet Zyrtec without the approval of your veterinarian.
  • Do not give your dog Zyrtec-D because it contains pseudoephedrine, which is highly toxic to dogs.
  • Zyrtec has not been evaluated for safety during pregnancy or lactation and should not be used in either situation.
  • Use with caution in pets with seizure disorders, thyroid problems, prostatic enlargement, glaucoma, and heart, liver, or kidney disease.
  • Zyrtec syrup is preserved in propylene glycol and should not be used in cats.
  • Disintegrating tablets may contain xylitol, a sweetener which is toxic to dogs.

Read more:

Medication Info Sheet: Claritin

Ditch the Itch: Skin Allergies in Dogs

Diagnosing and Treating Environmental Allergies in Dogs

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