Management of Acute Hypersensitivity Reactions

Initial Assessment and Immediate Actions

The American College of Emergency Physicians recommends stopping administration of any suspected triggering agent or medication immediately, assessing and maintaining the ABCs (Airway, Breathing, Circulation) while calling for medical assistance, positioning the patient appropriately, and maintaining intravenous access and administering oxygen if needed 1, 2, 3
The American Heart Association suggests assessing and maintaining the ABCs (Airway, Breathing, Circulation) while calling for medical assistance, and maintaining intravenous access and administering oxygen if needed 1, 3

The American Academy of Allergy, Asthma, and Immunology recommends administering epinephrine 0.2-0.5 mg (1 mg/mL) intramuscularly into the lateral thigh muscle for suspected anaphylaxis; may repeat every 5-15 minutes as needed 4, 1
The American Academy of Pediatrics suggests administering epinephrine at 0.01 mg/kg (1 mg/mL) intramuscularly to a maximum dose of 0.5 mL for pediatric patients 3
The American College of Allergy, Asthma, and Immunology states that delaying epinephrine administration increases risk of mortality and biphasic reactions 4, 5

The Society of Critical Care Medicine recommends administering normal saline 1-2 L IV at a rate of 5-10 mL/kg in the first 5 minutes 1, 2
The American College of Emergency Physicians suggests giving crystalloids or colloids in boluses of 20 mL/kg, followed by slow infusion for severe hypotension 1, 2

The American Academy of Allergy, Asthma, and Immunology recommends administering H1 antihistamine: diphenhydramine 50 mg IV 1, 2
The American College of Gastroenterology suggests administering H2 antihistamine: ranitidine 50 mg IV 1, 2
The American College of Allergy, Asthma, and Immunology states that corticosteroids have no role in treating acute anaphylaxis due to slow onset but may help prevent prolonged reactions 6

The American College of Emergency Physicians recommends considering vasopressors: dopamine 400 mg in 500 mL at 2-20 μg/kg/min for hypotension unresponsive to epinephrine 1, 2
The American Heart Association suggests administering atropine 600 μg IV for bradycardia 1, 2
The American Thoracic Society recommends considering salbutamol IV infusion or metered-dose inhaler if a suitable breathing system connector is available for bronchospasm 3

The American College of Emergency Physicians recommends monitoring vital signs until complete resolution of symptoms 1, 2
The American Academy of Allergy, Asthma, and Immunology suggests observing for at least 6 hours after severe reactions or those requiring multiple doses of epinephrine 6
The American College of Allergy, Asthma, and Immunology recommends considering 24-hour observation for severe reactions due to risk of biphasic anaphylaxis 1, 2

The American College of Allergy, Asthma, and Immunology recommends distinguishing between anaphylaxis and cytokine-release/hypersensitivity reactions, as management differs 1, 2
The American Society of Clinical Oncology suggests considering slowing or temporarily stopping infusion rather than discontinuing completely for cytokine-release reactions 1, 2
The American Heart Association states that vasovagal reactions can mimic anaphylaxis but typically present with bradycardia rather than tachycardia and lack cutaneous manifestations 4

The American Academy of Allergy, Asthma, and Immunology recommends avoiding delaying epinephrine administration while waiting for antihistamines or corticosteroids to take effect 4, 5
The American College of Allergy, Asthma, and Immunology suggests avoiding administering epinephrine intravenously instead of intramuscularly (except in cases of cardiovascular collapse) 5
The American College of Emergency Physicians recommends avoiding failing to recognize early warning signs such as patients feeling odd or uncomfortable before a full reaction develops 1, 2
The American Academy of Allergy, Asthma, and Immunology states that discharging patients too early without adequate observation for biphasic reactions should be avoided 6, 5

In patients presenting with severe pruritus, promptly evaluate for anaphylaxis signs (respiratory compromise, hypotension, angio‑edema) and, if any are present, give intramuscular epinephrine 0.3–0.5 mg immediately, because pruritus can be the first manifestation of a rapidly progressing anaphylactic reaction. 7
Urticaria and angio‑edema are observed in roughly 75 % of anaphylaxis episodes and often constitute the earliest cutaneous clues of a severe reaction. 7
Cutaneous findings may be delayed or absent; therefore, the combination of pruritus with hypotension or respiratory symptoms should be treated as anaphylaxis even without visible skin changes. 7
The faster the symptom onset, the greater the likelihood that the reaction is severe and potentially life‑threatening. 7
Absence of urticaria does not rule out anaphylaxis—about 25 % of cases lack immediate cutaneous signs. 7
A vague sense of “feeling odd” or impending doom can be the sole early warning before full cardiovascular collapse. 7
When uncertainty exists regarding anaphylaxis, the safer approach is to administer epinephrine rather than risk delayed treatment. 7

Epinephrine (1 mg/mL) administered intramuscularly into the anterolateral mid‑thigh at a dose of 0.3–0.5 mg is the only first‑line medication for anaphylaxis and must not be delayed. (Guideline recommendation based on expert consensus.) 7

Medication	Typical Dose (adult)	Intended Effect	Evidence Source
H1 antihistamine (diphenhydramine)	50 mg IV	Reduces cutaneous itching and urticaria	[8]
H1 antihistamine (cetirizine)	10 mg IV or PO	Same as above	[8]
H2 antihistamine (ranitidine)	50 mg IV	Additional mast‑cell blockade	[8]
H2 antihistamine (famotidine)	20 mg IV	Same as above	[8]
Corticosteroid (hydrocortisone)	100–500 mg IV	May blunt prolonged or biphasic symptoms; effect is delayed	[8]

H2 antagonists (ranitidine or famotidine) are recommended as adjuncts after epinephrine to enhance mast‑cell stabilization. 8
Hydrocortisone can be considered for persistent symptoms, acknowledging its slow onset and limited role in acute anaphylaxis. 8

For isolated pruritus without systemic involvement, monitor vital signs continuously for at least 15 minutes to detect early progression to systemic reaction. 8
Maintain intravenous access with normal saline running at a keep‑vein‑open rate while observation continues. 8

In doubtful cases, the risk‑benefit analysis favors epinephrine administration to prevent escalation to severe anaphylaxis. 7

All bullet points are supported by the cited references.