Management of sudden allergic reaction (itching all over the body)
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urticaria anaphylaxis acute allergic reaction management
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acute allergic reaction generalized itching urticaria management 2025 guidelines
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https://www.aaem.org/statements/clinical-practice-guideline-…
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Management of Sudden Allergic Reaction (Generalized Itching / Urticaria)
Step 1: First - Assess Severity (Grading)
Before treating, quickly classify the reaction because management differs by grade:
| Grade | Features |
|---|---|
| I | Localized skin reaction only (small area) |
| II | Widespread urticaria / generalized itching |
| III | Respiratory symptoms: wheeze, bronchospasm, angioedema |
| IVa | Airway involvement: tongue swelling, hoarseness, laryngeal edema |
| IVb | Cardiovascular collapse: hypotension, circulatory collapse |
Generalized itching all over the body is typically Grade II. Management below covers Grade II and escalation steps if needed.
Step 2: Remove the Trigger
- Stop the offending drug, food, or substance immediately.
- If reaction followed oral ingestion and is Grade II or above, activated charcoal 1 g/kg orally may reduce further absorption.
Step 3: Drug Treatment
A. H1 Antihistamines (First-Line for All Grades)
These are the cornerstone of treatment. They relieve pruritus, reduce number, size, and duration of hives.
-
Second-generation (preferred for outpatient/mild-moderate):
- Cetirizine 10 mg oral
- Loratadine 10 mg oral
- Fexofenadine 180 mg oral
- Desloratadine 5 mg oral
- Advantage: Less sedation, better tolerated
-
First-generation (effective but sedating - useful at night or when rapid effect needed):
- Diphenhydramine (Benadryl) 25-50 mg oral/IM
- Hydroxyzine 25-50 mg oral
- Note: Causes sedation, anticholinergic effects
Practical tip: Many dermatologists use a combination - a non-sedating H1 antihistamine during the day + a sedating one at night.
B. H2 Antihistamines (Add-on if H1 alone is insufficient)
- Ranitidine or famotidine may be added when symptoms are not controlled by H1 blockers alone.
- H1 + H2 combination can be more effective than H1 alone for urticaria.
C. Corticosteroids (for moderate-severe or unresponsive cases)
Indicated when symptoms are severe, not responding to antihistamines, or if angioedema is present:
- Prednisolone 0.5-1.0 mg/kg/day orally (with or without a short taper)
- Methylprednisolone IV for inpatient use
- Mechanism: Suppresses leukotriene/prostaglandin formation and cellular immune response.
- Note: A short course is appropriate for acute urticaria; long-term steroids are NOT recommended.
Step 4: Escalation for Anaphylaxis (Grade II and above with systemic features)
If the reaction progresses beyond simple itching (wheeze, hypotension, throat swelling), escalate immediately:
-
Adrenaline (Epinephrine) - MOST IMPORTANT drug
- 0.01 mL/kg (up to 0.5 mL) of 1:1000 solution IM/SC
- Repeat every 15 minutes as needed
- For anaphylaxis with respiratory distress: 0.3 mg IM/SC (0.3 mL of 1:1000) every 10 minutes
- This is Grade A, Level I evidence (AAEM guideline)
-
Oxygen - 40-100% concentration
-
Beta-2 agonist - Salbutamol (albuterol) via nebulization if bronchospasm present
-
Aminophylline - IV infusion if bronchospasm persists despite salbutamol
-
IV Fluids - 10-30 mL/kg, titrated to response for hypotension
-
Diphenhydramine - Antihistamine of choice in the acute/severe setting
Step 5: Indications for Hospital Admission
- Laryngeal edema - admit to ICU
- Severe symptoms not responding to antihistamines
- Respiratory distress or anaphylaxis
- Cardiovascular compromise
Medications to Avoid
- Aspirin and NSAIDs - can worsen urticaria and angioedema
- ACE inhibitors - associated with angioedema
- Opioids - can cause direct mast cell degranulation and worsen reactions
- Antileukotrienes (montelukast) - no proven role in acute urticaria/angioedema
Quick Summary Table
| Scenario | Treatment |
|---|---|
| Mild generalized itching (Grade II) | Oral 2nd-gen antihistamine (cetirizine/loratadine) |
| Not responding to H1 alone | Add H2 antihistamine |
| Moderate-severe / angioedema | Add oral/IV corticosteroid |
| Anaphylaxis / respiratory distress | Epinephrine IM/SC + oxygen + corticosteroid + antihistamine |
| Laryngeal edema | ICU admission + epinephrine |
Sources:
- The Essentials of Forensic Medicine and Toxicology, 36th ed. - Grades of Anaphylaxis and Management (p. 545)
- AAEM Clinical Practice Guideline: Acute Urticaria/Angioedema - Grade A, Level I evidence
- 2024 International Urticaria Guidelines (EAACI/GA2LEN/EDF/WAO) - updated December 2024
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