Antihistamines for Dogs

This page looks at antihistamines for dogs - antihistamines such as Benadryl are often used as dog allergy medication to relieve symptoms such as itchiness. How exactly do antihistamines work? Are there any adverse side-effects? Read on and find out.

Besides corticosteroids, antihistamines are another type of dog allergy medication frequently used by veterinarians to relieve the itchiness in the allergic dog.

What is Histamine and How Do Antihistamines Work?

Histamine is a chemical that is released by mast cells in an allergic dog's body in response to an exposure to allergens such as pollens, mold, house dust mites, etc. The released histamine locks onto histamine receptors (called H1 receptors) which are located on various cells in the dog's body. When that happens, the cells undergo biochemical changes and produce allergy symptoms such as itching, runny eyes and runny nose. Histamine receptors also release other chemicals that increase inflammation, resulting in inflammation of the skin in the allergic dog.

Antihistamines work by physically preventing (blocking) histamine from connecting with its histamine receptor, thus preventing the biochemical changes which produce the allergy symptoms.

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How Effective Are Antihistamines for Dogs

Various studies on the effectiveness of antihistamines on dogs have been conducted with variable results. Specifically, about 10 to 30 percent of dogs have been found to show improvement after using antihistamines for their allergies.

Compared with corticosteroids, antihistamines are not as effective because antihistamines block only the histamine receptors on cells in the body. However, histamine is not the only chemical released by the mast cells. Other chemicals released can also cause allergy symptoms such as itching.

In addition, antihistamines for dogs work best when taken before allergy symptoms are evident - they are not so effective if taken when the allergic dog is already showing signs such as severe itching.

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What Are Some Common Antihistamines for Dogs?

Some common antihistamines for dogs include:

Benadryl (diphenhydramine)
Atarax/Vistaryl (hydroxyzine)
Chlortrimeton (chlorpheniramine)
Tavist (clemastine)
Periactin (cyproheptadine)
Temaril (trimeprazine)

Different dogs react to antihistamines differently. If you are lucky, you may get an antihistamine that works for your dog first time round. On the other hand, there is also a possibility that none of the antihistamines work! Only by trial and error can we determine which antihistamine works best for our dog.

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What Are Some Possible Side Effects of Antihistamines on Dogs?

Antihistamines seem relatively safe to be used to treat dog allergies. The one major side effect is sedation - your dog may be sleepy when taking this medication. In some cases, sedation wears off in a few days.

Dogs with liver disease should use antihistamines with caution since antihistamines are metabolized by the liver. To strengthen the liver and support liver function, you may want to give a supplement (such as Thorne Research Hepagen-C) that contains the herb milk thistle to your dog to help detoxify his liver while he is on antihistamines.

As well, dogs with the following conditions should not use antihistamines:

Glaucoma
Urinary retention disorders
Pregnancy

Some natural remedies can be used to relieve allergy symptoms in dogs. Visit our page on Natural Allergy Relief for more information. For other treatment options, visit How to Treat Dog Allergies.
Also use the navigation bar on the left of this page to get access to more information on other canine allergies and skin problems.