Benadryl for mast cell tumors? What on earth does an over-the-counter allergy medicine have to do with cancer?? Let’s find out.
Most of us have heard of Benadryl, the brand name for diphenhydramine hydrochloride. It’s an antihistamine, which means it reduces the effects of excess histamines in the body.
In human medicine, we usually use it for allergies: hay fever, runny eyes, sneezing, and allergic sinus congestion. It is also used for more sudden-onset allergic reactions, including hives, facial swelling and so on.
In veterinary care, we use it to treat things like insect stings, vaccine reactions or other allergic reactions in dogs.
And we often recommend Benadryl for dogs suffering from mast cell tumors.
Dogs with cancer are not experiencing allergies. So, what’s the logic?
Dr. Dressler goes into deep detail on Mast Cell Tumors in his audio seminar.
Well, it turns out there are similarities between a dog with a high mast cell burden and a dog experiencing allergic flare-ups. And Benadryl for mast cell tumors can address those.
Mast Cells Are Weird and Cool
Mast cells are really interesting cells. They are part of the immune system, a type of white blood cell.
Mast cells help rid the body of foreign invaders or material. They also help in healing. They do this in part by generating a substance called histamine. Yup, the same histamine that we talk about when it comes to allergies.
Mast cells that are normal release histamine as part of their work. Histamine helps attract other white cells to trouble spots, like foreign bacteria, or viruses, or injuries. They’re like those red flags your car’s roadside safety kit has. Histamine “marks” an area of the body that is in trouble, so other immune cells can find the area.
Histamine also causes blood vessels to dilate (get larger), and get a little “leaky.” The increased blood flow brings more white blood cells more quickly, and the little leaks help the white blood cells slip out of the blood and into the area that needs them.
So, you see, histamine is an important part of our immune system.
Mast Cell Detects Trouble ==> Releases Histamine ==> Attracting Other Immune Cells ==> Which Kill Invaders and/or Repair Injuries
So, yay histamine, right?
Yes. Mast cells are cool, because they produce histamine. Until they produce too much.
Mast Cells Can Overdo It
As with all things, balance is needed when it comes to histamine. Too much histamine is not good for the body.
When mast cells release too much histamine, whether during an allergic reaction or by huge numbers of cancerous mast cells, bad things happen.
- The blood vessels in the area of the mast cells dilate, bringing inflammation and swelling of body tissues. In allergic reactions, this looks like hives and abnormal swelling.
- The excess histamine is capable of causing the lining of the stomach to produce excessive acid. This causes loss of appetite and lethargy.
- Blood pressure can be affected if enough histamine is secreted. It can drop to truly dangerous levels as many blood vessels open up all at once.
As it turns out, when a lot of mast cells are busy releasing their contents, they secrete lots of things, not only histamine. There are other chemical signals that work in tandem with the histamine, and those get released, too.
The end result of all these mast cells releasing their chemical signals is that the dog’s body goes into a completely abnormal state.
Inflammation and swelling results, and discomfort, as well. I would imagine the sensation is like getting stung or perhaps old stings (itchy, burning). Those with allergies might be familiar with the feeling of all-0ver discomfort, a sort of panicky itchy weird feeling. I imagine it is something like that for our dogs who have a massive release of histamine.
Histamine and Mast Cell Tumors
Now, both cancerous and non-cancerous mast cell tumors are capable of releasing histamine, and both are capable of releasing too much.
If your dog has allergies, you might see a little swelling or redness, and itching. Same is true if your dog has mast cell tumors.
But NOT every mast cell tumor will release very high levels of histamine that cause terrible symptoms like those above.
So if your dog has mast cell tumors, don’t assume that you will see those symptoms.
Only the most severe cases will have these high levels of histamine release.
Why We Use Benadryl for Mast Cell Tumors
Benadryl blocks the effects of histamine in the body, which is why it’s called an “antihistamine.”
Basically, it helps the body cope with abnormally high histamine levels.
That’s why you might hear your veterinarian recommend it for your dog with mast cell tumors: it can help to block the uncomfortable-to-dangerous effects of excess histamine released by cancerous mast cells.
Benadryl can help with the side effects of excess histamine sometimes associated with mast cell tumors.
Remember how excess histamine can also affect the stomach, by causing extra stomach acid? Benadryl helps with that, too. However, sometimes veterinarians will also suggest using an antacid as well, just to be sure to protect the tummy. Cimetidine and famotidine (Tagamet and Pepcid) are often used, and ulcers (if they are present) are often treated with misoprostol (Cytotec) and sucralfate (Carafate).
If your dog with mast cell tumors is also experiencing excess histamine release — and remember, not all do — there are special dietary considerations you should also be aware of. You can read more about special nutritional choices for dogs with mast cell tumors in this article.
Of course, diet is just one of five steps in my Full Spectrum approach to cancer care. In addition to diet, nutraceuticals, anti-metastatic supplements, and mind-body strategies, you can find an entire chapter on the conventional care for mast cell tumors in chapter 30 of The Dog Cancer Survival Guide.
All my best,
If your dog has mast cell tumors, this book is a wealth of information. In addition to the main steps Dr. D recommends, read the extra chapter dedicated to mast cell tumors from Dr. Ettinger, his oncologist co-author.
Dr. Demian Dressler is internationally recognized as “the dog cancer vet” because of his innovations in the field of dog cancer management, and the popularity of his blog here at Dog Cancer Blog. The owner of South Shore Veterinary Care, a full-service veterinary hospital in Maui, Hawaii, Dr. Dressler studied Animal Physiology and received a Bachelor of Science degree from the University of California at Davis before earning his Doctorate in Veterinary Medicine from Cornell University. After practicing at Killewald Animal Hospital in Amherst, New York, he returned to his home state, Hawaii, to practice at the East Honolulu Pet Hospital before heading home to Maui to open his own hospital. Dr. Dressler consults both dog lovers and veterinary professionals, and is sought after as a speaker on topics ranging from the links between lifestyle choices and disease, nutrition and cancer, and animal ethics. His television appearances include “Ask the Vet” segments on local news programs. He is the author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog’s Life Quality and Longevity. He is a member of the American Veterinary Medical Association, the Hawaii Veterinary Medical Association, the American Association of Avian Veterinarians, the National Animal Supplement Council and CORE (Comparative Orthopedic Research Evaluation). He is also an advisory board member for Pacific Primate Sanctuary.