Why Benadryl For Mast Cell Tumors? - Dog Cancer Blog

Featuring Demian Dressler, DVM and Susan Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide.

≡ Menu

Why Benadryl For Mast Cell Tumors?

Most of us have heard of Benadryl.  In human medicine, we usually use it for allergies.  You know, hay fever, runny eyes, sneezing, and allergic sinus congestion.

It is also used for more sudden-onset allergic reactions with hives, facial swelling and so on.

In veterinary cancer care, Benadryl is often recommended for dogs suffering from mast cell tumors.

Since these dogs are not experiencing allergic reactions, what is the logic? Well, there actually are some similarities between a dog with a high mast cell burden and a dog experiencing allergic flare-ups.

Here is how it works.

Mast cells are a type of white blood cell in the body.  They normally operate to help rid the body of foreign invaders or material. They also help in healing.

These cells contain a substance called histamine.  Yes, just like the root of the word antihistamine. Both cancerous and non-cancerous mast cell tumors are capable of releasing histamine.

Histamine is useful in the body at certain levels.  Mast cells release histamine which helps attract other white cells to an area or an invader to help clean up the area, or mount an immune system reaction.

Histamine causes blood vessels to dilate (get larger) and get a little leaky. This lets more white cells and blood flow into an area.  The leaky parts let white cells slip out of the vessels to get to the site of injury or invader.  Histamine is important in immunity.

However, too much histamine is not good for the body.

When too much histamine is released by mast cells in the body, whether during an allergic reaction, or by huge numbers of cancerous mast cells, bad things happen.

As it turns out, when a lot of mast cells are busy releasing their contents, they secrete a lot of things.  Histamine is one of them. There are still more chemical signals that work in tandem with the histamine.

The end result of all these mast cells releasing their chemical signals is that the dog’s body goes into a completely abnormal state.

The blood vessels in the area of the mast cells dilate. Inflammation and swelling of body tissues accompanies the release of mast cell contents. Discomfort results as well. I would imagine the sensation is like getting stung or perhaps old stings (itchy, burning).

The excess histamine is capable of causing the lining of the stomach to produce excessive acid. This stomach acid contributes to the loss of appetite and lethargy seen in some cases of mast cell cancer.

If enough histamine is secreted, the blood pressure can drop due to dangerous levels.  This is because massive mast cell activity causes many blood vessels to open up, which is causes the pressure in the vessels to drop.

Of course, we must recall that there are many different forms of mast cell tumors with different behaviors.  Only the most severe ones will have these levels of histamine release.

Benadryl is useful in blocking the effects of the histamine in the body. It’s antihistamine effect helps the body cope with these abnormally high histamine levels.

In addition, the antacids cimetidine and famotidine (Tagamet and Pepcid) are often used in dogs to block the excess acid secretion caused by the histamine excess. Ulcers are often treated with misoprostel (Cytotec) and sucralfate (Carafate).

Other aspects of conventional care for mast cell tumors are found in The Dog Cancer Survival Guide.

All my best,

Dr D

About the Author: Demian Dressler, DVM


Dr. Demian Dressler, DVM is known as the "dog cancer vet" and is author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog's Life Quality and Longevity.

Leave a Comment