- Definition
- Acute, life-threatening hypersensitivity reaction involving multiple organ systems
- Usually IgE-mediated; can also be non-IgE or idiopathic
- Common triggers
- Foods (e.g. nuts, shellfish)
- Drugs (e.g. penicillin, NSAIDs)
- Insect stings
- Latex, contrast agents, exercise
- Pathophysiology (simplified)
- Re-exposure to allergen triggers IgE on mast cells and basophils
- This leads to degranulation and release of:
- Histamine, leukotrienes, prostaglandins, and other mediators
- These cause:
- Vasodilation and capillary leak → hypotension and shock
- Bronchoconstriction and mucosal edema → airway obstruction
- Smooth muscle activation in the GI tract and elsewhere → symptoms like vomiting, diarrhea, cramps
- Clinical features
- Sudden onset (minutes to 1–2 hours post-exposure)
- Skin: urticaria, flushing, angioedema
- Respiratory: wheeze, stridor, dyspnea
- Cardiovascular: hypotension, collapse
- GI: nausea, vomiting, abdominal pain
- Diagnosis
- Clinical — based on acute symptoms in response to known or likely allergen
- Serum tryptase (supportive)
- Allergen testing in follow-up
- Management
- IM adrenaline immediately
- Adults and children >12 years: 0.5 mg IM (0.5 mL of 1:1000 solution)
- Airway and circulatory support
- Antihistamines, steroids, bronchodilators as adjuncts
- Observe for biphasic reaction
- Prescribe EpiPen, refer to immunology