BRAND NAME: ZIRTEC
Histamine is an inflammatory biochemical that causes skin redness, swelling, pain, increased heart rate, and blood pressure drop when it binds to one of many H1 receptors throughout the body. Histamine is an important mediator of allergy in humans, hence a spectacular array of different antihistamines has proliferated. Histamine, perhaps unfortunately, is not as important a mediator of inflammation in pets, which means results of antihistamine therapy are not as reliable in pets, particularly dogs, when it comes to itchiness.
Most human antihistamines can be used in pets so long as they do not include decongestants or pain relievers in their formulations. As with humans, most antihistamines have drowsiness as a major side effect. The need for antihistamines that do not induce drowsiness led to the development of cetirizine. Hydroxyzine, another popular antihistamine is metabolized in the body to cetirizine which retains antihistamine properties without crossing into the brain and causing drowsiness.
HOW THIS MEDICATION IS USED
Cetirizine is an antihistamine and it is used for acute inflammatory and allergic conditions such as:
Managing itchy skinIn the past, antihistamines have been used more widely in the management of itch and allergy but recent work has not been able to demonstrate a clear positive effect from antihistamines directly, either for acute allergy flare ups or in the long term management of itch. Antihistamines seem best used concurrently with corticosteroids (such as prednisone) to enable a lower corticosteroid dose to be just as effective as a higher one.
Mast cell tumors are tumors involving cells that contain granules of histamine. Patients with mast cell tumors experience chronic inflammatory symptoms due to circulating histamine. Antihistamines such as diphenhydramine may be helpful given long term though cetirizine could also be used.
For more details on mast cell tumors click here.
Cetirizine is a member of the piperazine class of antihistamines. When different antihistamines are being tried and one appears ineffective, it is felt that the subsequent choice should be of a different class to avoid the likelihood of another failure.
Because cetirizine does not cross into the nervous system, side effects common to other antihistamines, such as dry mouth or heart rate elevation, are rare.
Drowsiness is still reported in 13% of people who take cetirizine.
The biggest problem with long term antihistamine use is the development of tolerance. This means that the body may eventually fail to respond to the medication as well as it did initially. Happily, tolerance is not felt to occur with cetirizine use.
INTERACTIONS WITH OTHER DRUGS
Cetirizine should not be used with additional tranquilizing medications.
CONCERNS AND CAUTIONS
When using an antihistamine to prevent an allergic reaction (such as a vaccine reaction) the antihistamine works best when given prior to the allergen.
This medication will interfere with allergic skin testing. Check with your veterinary dermatologist regarding how far in advance this medication should be withheld.
There is a formulation of cetirizine which includes a decongestant for human use. This product is not appropriate for animal use because of its toxicity potential.
Page last updated: 9/18/2014