A dog and cat relax on the couch together.

Anaphylactic Shock in Dogs and Cats

Anaphylaxis is a life-threatening condition that involves multiple organ systems as a result of an allergic reaction. Shock results from massive dilation of the blood vessels, histamine release, and low blood pressure. This leads to a high heart rate, which can cause cardiovascular collapse and, potentially, death. Clinical signs will usually occur within the first 30 minutes after exposure to the allergen and will worsen rapidly. The faster the signs appear, the more severe the anaphylaxis will be.

Common Causes of Anaphylaxis

Often, a definitive cause for anaphylactic shock is not found and a diagnosis is made on clinical signs alone. However, some common causes can be identified based on history and physical examination.

Clinical Signs of Anaphylactic Shock

Dogs and cats have different physiologic reactions to anaphylaxis. Dogs primarily have histamine release from the gastrointestinal tract, which results in vomiting, bloody diarrhea, and collapse. Cats primarily have respiratory signs with anaphylaxis including bronchoconstriction (airway constriction).

Common Clinical Signs in Dogs:

Common Clinical Signs in Cats:

Signs of Anaphylactic Shock

Treatment of Anaphylaxis

Anaphylaxis is a life-threatening emergency and immediate treatment is required. Due to the quick decline, time to start treatment is extremely important. Once you start to notice an allergic reaction starting, begin by removing the cause if identifiable (i.e. removing a bee stinger). Once your pet is at the veterinary clinic, they will be stabilized by administering of intravenous fluids, oxygen support, and additional medications (i.e. an antihistamine, epinephrine, bronchodilators). Severe cases may require plasma transfusions, blood transfusions, or ventilation. Your pet will likely be hospitalized for close monitoring for at least 24-48 hours.

Preventing Anaphylaxis in the Future

Treatment of anaphylactic shock is entirely based on the progression and signs as they develop. Prevention of anaphylaxis is comprised of avoiding an inciting substance or food, pre-medication for pets that have had a previous reaction (i.e. vaccine reaction), and having medications at home, including diphenhydramine (Benadryl).


Shmuel, Daniella L., and Yonaira Cortes. Anaphylaxis in dogs and cats. Journal of Veterinary Emergency and Critical Care 23.4. 2013: 377-394.