Anaphylaxis — Recognition & Treatment

Key Points

• Epinephrine is first-line therapy and should be given intramuscularly in the lateral thigh as soon as anaphylaxis is suspected.
• Do not wait for rash, tryptase, IV access, or diagnostic certainty before treating a convincing reaction.
• Repeat IM epinephrine every 5 to 15 minutes when symptoms persist or recur.
• Shock often requires rapid isotonic crystalloid in addition to epinephrine because capillary leak and vasodilation can be profound.
• Antihistamines treat cutaneous symptoms only and are not substitutes for epinephrine.
• Corticosteroids have no role as immediate rescue therapy and should never delay epinephrine.
• Refractory anaphylaxis is best managed with a titrated IV epinephrine infusion in a monitored setting, not routine IV epinephrine boluses.
• Discharge planning should include epinephrine access, technique training, trigger evaluation, and a written emergency plan.

Algorithm

1. Recognize acute multisystem allergic symptoms, airway compromise, bronchospasm, or hypotension after a plausible trigger.
2. Give IM epinephrine immediately and position the patient to support circulation.
3. Assess airway and breathing, provide oxygen when needed, and establish monitoring and IV access.
4. Repeat IM epinephrine for persistent symptoms and give rapid isotonic crystalloid for hypotension.
5. Add inhaled beta agonist for residual bronchospasm and H1 antihistamine only for persistent skin symptoms after stabilization.
6. For refractory shock, begin a titrated IV epinephrine infusion with critical-care level monitoring; consider glucagon in beta-blocked patients.
7. Observe according to reaction severity, treatment requirements, comorbidities, trigger, and access to emergency care.
8. At discharge, prescribe or replace epinephrine autoinjectors as appropriate, demonstrate use, provide an action plan, and arrange allergy follow-up.

Clinical Synopsis & Reasoning

Suspect anaphylaxis when acute illness follows a plausible exposure and involves multiple organ systems, or when there is acute hypotension, laryngeal involvement, or bronchospasm after a known or highly probable allergen. Common findings include generalized urticaria, flushing, angioedema, throat tightness, hoarseness, stridor, wheeze, dyspnea, abdominal cramping, vomiting, diarrhea, dizziness, syncope, and shock. Skin findings may be absent, particularly in severe cardiovascular reactions. Ask about foods, medications, insect stings, biologics, latex, exercise, co-factors such as alcohol or NSAIDs, and previous reactions, but do not delay treatment to identify the trigger. Place the patient supine with legs elevated when tolerated; sudden upright positioning in shock can worsen venous return. Pregnancy generally favors left lateral positioning. Continuously reassess airway edema, respiratory effort, oxygenation, blood pressure, mental status, and response to epinephrine. Serum tryptase can support retrospective confirmation in selected cases when obtained within an appropriate time window and compared with a later baseline, but a normal result does not exclude anaphylaxis. Differential diagnoses include vasovagal syncope, isolated urticaria, asthma, panic, hereditary angioedema, vocal cord dysfunction, septic shock, and other causes of acute hypotension.

Treatment Strategy & Disposition

Give intramuscular epinephrine promptly in the mid-anterolateral thigh. A common adult dose is 0.3 to 0.5 mg of 1 mg/mL solution, or 0.01 mg/kg up to 0.5 mg, repeated every 5 to 15 minutes according to response. There is no absolute contraindication to IM epinephrine in anaphylaxis. Provide high-flow oxygen when hypoxemic or severely ill, establish intravenous access, and give rapid isotonic crystalloid boluses for hypotension because profound vasodilation and capillary leak can require substantial volume. Nebulized albuterol can treat persistent bronchospasm but does not replace epinephrine. H1 antihistamines may reduce hives or itching after stabilization, but they do not reverse airway edema or shock. Corticosteroids have delayed onset and are not reliable acute rescue therapy or proven prevention for every biphasic reaction. Persistent hypotension or airway compromise despite repeated IM doses should prompt a monitored intravenous epinephrine infusion by clinicians familiar with titration rather than repeated intravenous boluses. Consider glucagon for refractory anaphylactic shock in a patient taking beta blockers. Secure a threatened airway early with experienced help because progressive edema can make later intubation difficult.

Epidemiology / Risk Factors

• Foods, medications, and insect venoms are common triggers, with prevalence varying by age and setting.
• Antibiotics, perioperative agents, and biologic therapies are important medication triggers.
• Exercise, infection, alcohol, NSAIDs, and other cofactors can lower the reaction threshold in susceptible individuals.
• A previous mild reaction does not guarantee that a future exposure will also be mild.
• Delayed epinephrine is repeatedly associated with worse outcomes in severe anaphylaxis.

Investigations

Common Triggers

Pharmacology

Prognosis / Complications

• Most patients respond promptly to one or more doses of IM epinephrine plus supportive care.
• Fatal anaphylaxis is uncommon but can progress rapidly through airway obstruction, severe bronchospasm, or distributive shock.
• Biphasic symptoms can recur after apparent resolution, with risk influenced by initial severity and need for repeated epinephrine.
• Future risk is reduced by trigger identification, avoidance strategies, access to epinephrine, and confidence in autoinjector use.
• Allergy evaluation can clarify uncertain triggers and, for selected allergens such as venom, identify preventive treatments.

Patient Education / Counseling

• Teach that epinephrine should be used at the first sign of a serious systemic reaction rather than saved until collapse.
• Demonstrate the exact autoinjector technique and advise carrying the recommended number of devices because a second dose may be needed.
• Call emergency services after epinephrine according to the action plan, particularly for severe symptoms, recurrence, or incomplete response.
• Review label reading, cross-contact, medication allergy documentation, insect avoidance, or other trigger-specific measures.
• Encourage specialist allergy follow-up to confirm the trigger, assess cofactors, and determine whether testing or immunotherapy is appropriate.

Notes

Anaphylaxis management is intentionally diagnosis-forward and treatment-forward. A patient does not need to meet every textbook feature before receiving epinephrine, and skin symptoms are not required in a severe reaction. The safest sequence is early IM epinephrine, physiologic support, repeated reassessment, and escalation to an epinephrine infusion when shock is refractory. Once the acute event is controlled, prevention becomes part of the medical treatment: identify the likely trigger, ensure access to epinephrine, teach correct use, provide a written plan, and arrange allergy assessment when appropriate.

References

1. 2023 Anaphylaxis Practice Parameter Update - AAAAI/ACAAI — Link