Zyrtec (cetirizine) is asecond generation antihistamine which can be used on cats to treat allergy related symptoms. Antihistamines work by blocking the effects of histamine on the certain cells within the body. When a cat has an allergic response, mast cells and basophils release histamine which binds to cells containing H1 receptors. Four types of receptors have been identified so far.
H1 – Located in the smooth muscles, lining of blood vessels and airways.
H2 – Found in the stomach cells and stimulates the secretion of stomach acid.
H3 – Located in the neurones of the brain, influences neurotransmission.
H4 – Found in the bone marrow and white blood cells. Responsible for immune response.
The effects of histamine on the H1 receptors includes the following:
Causes vasodilation (expansion) of the blood cells causes more blood to flow to the area and increases permeability, which makes them leaky. This allows white blood cells and blood plasma proteins to move out of blood vessel and migrate to the affected site. This leaking of fluid causes localised swelling.
Vasodilation also causes blood pressure to drop.
Bronchoconstriction is the constriction (or narrowing) of the airways in the lungs caused by the smooth muscle contracting.
Antihistamines are either first generation or second generation. First generation are older and generally cheaper to purchase however are able to cross the blood-brain barrier leading to sedative effect. They also have a shorter half life, meaning more frequent dosages are necessary. Zyrtec is a second generation antihistamine.
First generation antihistamines include:
Second generation antihistamines are newer, but often more expensive. Benefits of second generation include less drowsiness due to a lower blood-brain barrier penetration and a longer half-life, so once daily administration is usually all that is required (which is good when trying to pill cats). Second generation antihistamines include:
Throughout the article, I refer to this medication as Zyrtec, because that is what most pet owners call the product. Zyrtec is, in fact, the patented name for, cetirizine, but as it is now off-patent, there are many generic products available with the same ingredient as Zyrtec.
When purchasing Zyrtec (or its generic equivalent), let your pharmacist know it is for a cat, and make sure that cetirizine is the only active ingredient.
What are the symptoms of allergies in cats?
The symptoms of allergies in cats tends to manifest as skin disorders, symptoms may come and go depending on the underlying cause. Common symptoms of allergies in cats include:
Milinary dermatitis, small, dry, crusty papules
What can Zyrtec be used for in cats?
Zyrtec can be used to block the effects of histamine, therefore relieving symptoms of allergies such as itching, skin inflammation urticaria.
It can also be of help in treating eosinophilic granuloma complex, an inflammatory skin condition characterised by lesions affecting multiple areas of the body including the face, lips, in particular, the abdomen and thighs.
Zyrtec dosage for cats:
Tablets come in 10mg tablet or chew form. Dosage is 1/2 mg per pound or 1mg per kilo.
This dosage is based on a 5 kg cat.
5 mg (half a tablet) once a day.
Make sure the product doesn’t contain additional ingredients.
Zyrtec side effects:
Side effects are lower for second generation antihistamines, but may include:
Can Zyrtec be used on all cats?
Please consult your veterinarian before administering Zyrtec to your cat. It should not be used on the following cats unless told to do so by your veterinarian:
Cats with kidney disease
Cats with liver disease
Cetirizine or hydroxine sensitivity
There are a number of other antihistamines which are also used to treat cats with allergies. Cats will respond differently to each one. Some veterinarians will recommend an ‘antihistamine trial’. Your cat will be put on an antihistamine for 10 days to see if his symptoms improve, if they don’t, another antihistamine will be tried until one can be found which works with your cat.
Treatment of acute flares:
Initially, your cat may be put on steroids and antihistamines to relieve symptoms while the allergy is brought under control. In some cases, a secondary infection may have developed due to trauma to the skin. Antibiotics will be necessary to treat bacterial skin infections.
Once symptoms have improved, the steroids will be withdrawn and he will remain on the antihistamines as long as is necessary.
Other ways to reduce allergies in cats:
Finding and eliminating the cause of allergies is always the number one goal. This is not always as easy but steps can be taken to reduce your cat’s exposure.
If it is pollen, keep your windows closed during spring.
Buy a vacuum cleaner with a HEPA filter.
Carpeted flooring tends to hold on to allergens more readily than wooden floorboards.
Give your cat weekly baths with a suitable antipruritic shampoo to remove allergens from the coat.
Be diligent with flea control. Flea allergy dermatitis is an extremely common cause of allergies in cats.
Omega-3 fatty acids are also recommended for cats with allergies as they can help to reduce inflammation.
Immunotherapy may be tried in cats where the allergen is known. This works by administering a minute amount of the allergen to de-sensitise your cat. The ‘allergy shots’ will be tailored to use with each individual cat.