Anaphylaxis (Severe Systemic Type I Hypersensitivity)

By Robyn Hauser, DVM, DABVP, Deborah Miller, DVM, DABVP, and Carla Webb, DVM
Contributing Authors


An important step in the comprehensive evaluation of vaccination for a pet is to understand, and mitigate if possible, the potential risk of associated adverse events, including anaphylaxis. Although rare, anaphylactic reactions are a life-threating condition.

For this reason, it’s critical that the entire hospital team and the client know how to identify its early signs.

Table of Contents

Banfield Adverse Reaction Research

For the past five years, Banfield has measured the adverse reaction rates of vaccinations in our practice. While vaccine adverse events are historically underreported in the veterinary profession as a whole, Banfield’s electronic medical record system and relationships with our vaccine suppliers have allowed us to collect and trend such events in our locations.

We have found that anaphylaxis is rare, occurring only in 0.42/10,000 vaccine doses.1 Although rare, awareness of anaphylaxis and having a pre-defined response guideline may greatly reduce negative outcomes in affected patients.

What is Anaphylaxis?

Anaphylaxis is an acute systemic reaction due to a sensitivity to an allergen or stimulus that results in a massive release of inflammatory mediators. Clinical signs typically occur within minutes of exposure to the allergen, but may progress more slowly over several hours.

The effects of anaphylaxis are widespread, affecting multiple organs and body systems (e.g., cardiovascular, respiratory, coagulation cascade, inflammatory response, gastrointestinal (GI) system). There are countless potential triggers, including many drugs, vaccines, insect bites, parasiticides, and more.

Decreasing the Potential for Anaphylaxis

Previous exposure to an allergen suspected to cause anaphylaxis increases the risk for it to occur again. Unfortunately, previous exposure is not always recognized. Therefore, it’s important to take a thorough history including any previous potential vaccine reactions.

The development of adverse events may also be dependent on the genetics of an individual pet. Small-breed dogs experience a higher percentage of vaccine reactions, as do those dogs < 3 kg that receive multiple numbers of vaccine injections in the same visit.2

Providing pretreatment with diphenhydramine and closely observing high-risk breeds may decrease the potential for more severe reactions or allow for earlier intervention should a reaction occur.

Recognizing Signs of Anaphylaxis

Anaphylaxis does not present the same way in all patients. Both individual and species responses differ, and cats may present very differently than dogs.

Anaphylaxis in Dogs

In dogs, the primary shock organ is the GI tract and liver. Typically, vomiting, signs of nausea and defecation will occur in a dog experiencing anaphylaxis. However, the earliest signs are often increased agitation, excitation or hyperactivity.

As anaphylaxis progresses, respiratory distress or respiratory depression and cardiovascular collapse occur. Blood pressure may initially be normal or high but progresses to low blood pressure if untreated. Heart arrhythmias may develop, often with elevated heart rates. Mucus membranes may be pale or cyanotic.

Anaphylaxis in Cats

In cats, the primary shock organ is the respiratory tract. However, the earliest sign is often vomiting or severe pruritus (itching), especially of the face and head.

Severe respiratory distress is likely to ensue rapidly (can be due to bronchoconstriction, pulmonary edema and laryngeal edema), followed by cardiovascular collapse. Heart arrhythmias may develop with either an inappropriately low or even an elevated heart rate.

Pulse changes are observed, and mucus membranes may be pale or cyanotic. Although less likely in cats than dogs, agitation, salivation and incoordination may also be seen.

Anaphylaxis Treatment

The signs of impending systemic collapse will go undetected in the early stages of anaphylaxis unless patients are closely monitored (blood pressure, temperature, respiratory rate and effort, heart rate, pulse quality, mucus membrane color, level of consciousness).

For this reason, the successful treatment of anaphylaxis requires immediate, appropriate, aggressive treatment at the first signs of this life-threatening condition.

Banfield has developed a detailed treatment guideline for recommended anaphylaxis treatment (See Figure 1, below). 

Figure 1: Anaphylactic Reaction Treatment Protocol

This guideline was developed in consultation with emergency and critical care veterinary specialists and represents current “best practice” recommendations for treatment of this condition. 

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1. 2012 MQA data. Medical Quality Advancement team. Banfield Pet Hospital®. Portland, Ore.
2. Shearer P. Critically appraised topic (CAT): Vaccines. Banfield Journal. 2009;5(5):14-18.

About the Authors

Robyn Hauser, DVM, DABVP (Canine/Feline), is a graduate of the Oregon State College of Veterinary Medicine. Dr. Hauser has practiced small and exotic pet medicine in the Pacific Northwest for nearly 20 years and is currently a Senior Manager for the Medical Programs team for Banfield Pet Hospital® in Portland, Ore.

Deborah Miller, DVM, DABVP (Canine/Feline), graduated from the University of Florida’s College of Veterinary Medicine in 1990. She practiced emergency and critical care medicine for 10 years at several large referral practices in California prior to joining a general practice in Florida. She joined Banfield in May of 2009 as a medical advisor. She is currently Senior Manager/Medical Programs on Banfield’s Medical Quality Advancement team.

Carla Webb, DVM, graduated from Oregon State University in 2010. From 2008-2010, she worked with the Banfield Student Jobs Program and externship program, and joined Banfield full time in 2010. Dr. Webb was a clinical veterinarian in Banfield hospitals in Oregon for four years and is currently a Project Manager on Banfield’s Medical Programs team. Dr. Webb lives with her husband, Chris, and a crazy Siamese named Miso.