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Anaphylaxis is a life-threatening, immediate allergic reaction that can occur rapidly in response to exposure to an allergen, usually a medication, insect sting, or food. Without immediate emergency treatment, some affected dogs can die. It’s vital that dog owners learn to recognize its signs so they can get their dog to an emergency veterinarian without delay.

What Causes Anaphylaxis in Dogs?

Cases of anaphylaxis in dogs are increasing, likely because of the widening range of substances, vaccinations, and medications to which dogs are now exposed. “Anaphylaxis is considered a Type 1 hypersensitivity reaction,” explains AKC Chief Veterinary Officer Dr. Jerry Klein, DVM, “which means that the animal has been previously exposed to an antigen and then produces an excess of antibodies. When the antigen appears in the blood, the reaction can be systemic (body-wide) as in anaphylactic shock.”

Common causes include:

  • Insect stings from bees, wasps, hornets, and fire ants
  • Substances such as some chemotherapy drugs, vaccinations, contrast material, and antibiotics
  • Blood transfusions.
Viktoria Hadlaczki via Shutterstock

What Is Anaphylactic Shock?

Anaphylactic shock is a special case of anaphylaxis in which chemical changes brought on by anaphylaxis cause all the blood vessels to dilate, leading to inadequate blood and oxygen delivery throughout the body. This, in turn, causes the heart to race and the dog to collapse or even die from lack of blood to the heart and brain. Anaphylactic shock is an extreme emergency but, fortunately, is relatively rare.

“Anaphylactic shock is an emergency,” says Dr. Klein, who worked as an emergency veterinarian for over 30 years. “If you think that your dog is having an anaphylactic reaction, seek emergency veterinary assistance immediately. A veterinarian can give appropriate medications as intravenous injections to counteract the reaction. Additional treatment of anaphylaxis consists of the administration of fluids to control shock, corticosteroids, and antihistamines as needed.” Fortunately, notes Dr. Klein, “Anaphylactic shock is rare and not too commonly seen.”

Chihuahua getting a check-up at the vet.
FatCamera/Getty Images Plus

What Are Signs of Anaphylaxis in Dogs?

Owners often ignore signs of anaphylaxis because they assume their dog is just showing signs of less serious allergies. But anaphylaxis is both faster-acting and more severe.

“Slower onset hypersensitivity reactions are more commonly seen causing hives and/or facial swelling around the head, lips, muzzle, and around the eyes. The swelling can sometimes be so severe that the dog cannot open its eyes. These types of reactions are often caused by allergic reactions to drugs or vaccines, chemicals, something eaten, or insect bites. They generally develop within 20 to 60 minutes of exposure to the allergen (antigen),” explains Dr. Klein. “Hives and swelling are usually not life-threatening and typically go away by themselves if the source of the allergic reaction is removed or passes through the body. Veterinarians treat these reactions by giving appropriate medications such as antihistamines and corticosteroids.”

Dog owners may also overlook signs of anaphylaxis because they look for respiratory signs, which are the main symptom in humans. But dogs are different.

“Dogs differ from other domestic animals in that the major organ affected by anaphylaxis is the liver rather than the lungs,” Dr. Klein explains. “Gastrointestinal signs are the major signs of an anaphylactic reaction rather than respiratory signs. These signs include sudden onset of diarrhea, excessive salivation, vomiting, and, in extreme cases, a drop in blood pressure (shock), seizures, coma, and death. The dog’s gums may be pale, and the limbs may feel cold. The heart rate is generally very fast, but the pulse is weak.”

Golden Retriever laying down on a dog bed at home.
©demanescale -

In both people and dogs, the body releases histamine in response to an allergic or anaphylactic reaction. Histamine causes the blood vessels to dilate and increases gastric acids and heart rate. These cause clinical signs of runny nose, itching, difficulty breathing, low blood pressure, and rapid heart rate.

Signs of anaphylaxis in dogs include:

  • Reddening, swelling, itchiness, and raised areas (hives) on the face (since these initial signs may only last a short time, you or a veterinarian could miss them)
  • Drooling
  • Bloody diarrhea
  • Vomiting
  • Difficulty breathing; coughing, wheezing
  • Pale mucous membranes (or sometimes brick-red ones); decreased capillary refill time
  • Collapse
  • Racing heart rate with a weak pulse

Rapid onset is an important diagnostic clue. Anaphylaxis usually appears within 30 minutes after allergen exposure and worsens quickly. In general, the quicker signs appear, the more severe the anaphylaxis will be.

A veterinarian will diagnose a dog with anaphylaxis if its skin or mucous membranes are involved, along with breathing problems, incontinence, fainting, low blood pressure, vomiting, or diarrhea.

How Is Anaphylaxis in Dogs Treated?

Treatment depends on the dog’s particular signs, but should first focus on life-support even before diagnostics, as anaphylaxis can progress rapidly. The veterinarian will first ensure the dog can breathe, placing an endotracheal breathing tube or performing a tracheostomy if needed. Drugs to help dilate the breathing passageway may also help.

Rapid drug therapy is key to treatment. Drugs may include epinephrine, antihistamines, glucocorticoids, bronchodilators, vasopressors, and anticholinergics.

Epinephrine is the most essential drug for treatment. It constricts blood vessels, which leads to higher blood pressure, better circulation, and decreased swelling around the upper airway. It also increases the heart’s output and dilates the bronchi. Intravenous fluids may increase blood volume and pressure. In more severe cases, the dog may not respond to epinephrine and fluids. Other drugs, such as vasopressors, that increase the heart’s contractility may help.

Once the dog is responding, it should be hospitalized for 48 to 72 hours, as its organs can still quickly deteriorate.

Dalmatian laying on the floor in the living room at home.
alvarez via Getty Images

How Can You Guard Against Anaphylaxis in Dogs?

The most important step is recognizing the signs of anaphylaxis and getting to an emergency veterinarian quickly. It’s just as important to avoid or be ready for situations that could cause it.

“If a dog has been determined to have had a history of previous reactions to an agent, the safest prevention is to reduce or prevent any exposure to the antigen,” explains Dr. Klein. “In cases of needed vaccines, a veterinarian will often administer an antihistamine and/or corticosteroid about 20 to 30 minutes prior to vaccinating and will have the owner wait before going home to monitor for any concerning reactions.”

There’s no effective home treatment for anaphylaxis. Antihistamines cannot fight the massive cascade of internal chemicals that bring on anaphylactic shock. A dog will need epinephrine and possibly life support. For humans susceptible to anaphylaxis, a doctor would prescribe EpiPens that deliver epinephrine.

“At this time, there are no veterinary-labeled EpiPens specifically for use in dogs,” notes Dr. Klein. “Human formulated ones which come in various sizes may be able to be prescribed by a veterinarian as ‘off-label’ use, but there would need to be some form of documentation of a previous severe anaphylactic reaction for this to be prescribed.”

If your dog has a history of anaphylaxis, talk to your veterinarian about how you can be prepared, including the possible use of an EpiPen. Avoid any known allergens, and have a plan to get to the closest emergency vet, even if it’s not your own.

This article is intended solely as general guidance, and does not constitute health or other professional advice. Individual situations and applicable laws vary by jurisdiction, and you are encouraged to obtain appropriate advice from qualified professionals in the applicable jurisdictions. We make no representations or warranties concerning any course of action taken by any person following or otherwise using the information offered or provided in this article, including any such information associated with and provided in connection with third-party products, and we will not be liable for any direct, indirect, consequential, special, exemplary or other damages that may result, including but not limited to economic loss, injury, illness or death.

Related article: Dog Allergies: What You Need to Know