Contributor: Aaron Lessen, MD
Educational Pearls:
What is anaphylaxis and what are its treatments?
- Anaphylaxis is a broad term for potentially life threatening allergic reactions that can progress to cardiovascular collapse (anaphylactic shock).
- It is triggered by IgE and antigen cross-linking on mast cells to induce degranulation and the release of histamines, which can cause diffuse vasodilation and respiratory involvement with end-organ hypoperfusion.
- First line treatment is the immediate administration of epinephrine at 0.01 mg/kg (max dose for pediatrics is 0.3 mg and for adults is 0.5 mg) as well as removal of the offending agent causing the reaction.
- Additional pharmacologic treatments such as anti-histamines and steroids should be considered but not used instead of epinephrine when anaphylactic shock is evident as the sole therapy.
What is biphasic anaphylaxis and what is its occurrence?
- Biphasic anaphylaxis is the return of anaphylactic symptoms after the initial anaphylactic event. Previous studies have reported an incidence ranging from 1-20% of patients having an initial anaphylactic reaction having biphasic anaphylaxis, at a range of time from 1-72 hours.
- The mechanism of biphasic anaphylaxis is not completely known, but can be contributed to by initial interventions wearing off (and why patients will be monitored for 2-4 hours after initial symptoms and treatment), or delayed immune mediators beginning to take effect.
- Recent studies show that the rate of biphasic anaphylaxis may be closer to 16% occurrence with a median time of occurrence being around 10 hours.
What is the key take away and patient education on biphasic anaphylaxis?
- After patients have been observed for the initial 2-4 hours in the emergency room, they are generally safe to go home.
- Patients should be informed of the need to carry an Epi-Pen for similar anaphylactic reactions, and informed that there is a chance within the next day (10-20 hours) that they may have the symptoms occur once again.
- The biphasic reaction may be more mild, and patients should be educated on how to treat it and to seek immediate emergency care if the symptoms do not improve.
References
- Golden DBK, Wang J, Waserman S, et al. Anaphylaxis: A 2023 practice parameter update. Annals of Allergy, Asthma & Immunology. 2024;132(2):124-176. doi:10.1016/j.anai.2023.09.015
- Rubin S, Drowos J, Hennekens CH. Anaphylaxis: Guidelines From the Joint Task Force on Allergy-Immunology Practice Parameters. afp. 2024;110(5):544-546.
- Weller KN, Hsieh FH. Anaphylaxis: Highlights from the practice parameter update. CCJM. 2022;89(2):106-111. doi:10.3949/ccjm.89a.21076
- Gupta RS, Sehgal S, Brown DA, et al. Characterizing Biphasic Food-Related Allergic Reactions Through a US Food Allergy Patient Registry. The Journal of Allergy and Clinical Immunology: In Practice. 2021;9(10):3717-3727. doi:10.1016/j.jaip.2021.05.009
Summarized by Dan Orbidan OMS2 | Edited by Dan Orbidan & Jorge Chalit OMS4
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