Management of Scombroid Poisoning
Antihistamines are the cornerstone of treatment for scombroid poisoning, with H1-antihistamines (such as promethazine or diphenhydramine) administered orally or parenterally depending on severity, and H2-antihistamines often added as adjunctive therapy. 1, 2
Initial Assessment and Recognition
Scombroid poisoning presents within 10-30 minutes of ingesting contaminated fish (typically tuna, mackerel, or related species) with a characteristic clinical syndrome that mimics an acute allergic reaction 2, 3, 4:
- Cutaneous manifestations: Facial flushing spreading downward, erythema, urticaria affecting face and upper trunk, pruritus 2, 5, 3
- Cardiovascular symptoms: Palpitations, tachycardia, hot flushes, and potentially life-threatening hypotension 2, 4
- Gastrointestinal symptoms: Nausea, vomiting, abdominal cramping, diarrhea 2, 3
- Neurological symptoms: Headache, dizziness, facial numbness 2, 3, 4
- Respiratory symptoms: Bronchospasm (less common but can occur) 5
The fish may have a peppery or metallic taste, though this is not always present 2.
Treatment Algorithm
Mild Cases (Minor Symptoms, Hemodynamically Stable)
- Oral H1-antihistamines are sufficient for patients with mild cutaneous symptoms and no systemic compromise 2, 5
- Observation for 2 hours to ensure symptom resolution 2
- No specific treatment may be required if symptoms are resolving spontaneously 2
Moderate to Severe Cases (Major Toxicity)
- Parenteral H1-antihistamines (such as promethazine or diphenhydramine IV/IM) for patients with significant symptoms 2
- H2-antihistamines (such as famotidine) should be added as adjunctive therapy 1, 4
- Repeated doses may be necessary as symptoms can persist for up to 12 hours 2
- Hospital admission may be required for patients needing multiple doses or with persistent symptoms 2
Life-Threatening Presentations
For patients presenting with severe hypotension or cardiovascular compromise 4:
- Aggressive fluid resuscitation as first-line hemodynamic support 4
- Vasopressors (such as phenylephrine) if hypotension is refractory to fluids 4
- Antihistamines (both H1 and H2) administered parenterally 4
- Continuous cardiac monitoring with ECG to assess for tachycardia, ST changes, or arrhythmias 4
- Management parallels that of acute anaphylaxis for severe cases 2
Critical Pitfalls to Avoid
Do not misdiagnose scombroid poisoning as fish allergy - this is a toxin-mediated histamine response, not an IgE-mediated allergic reaction, and patients can safely consume properly stored fish of the same species in the future 2, 5. The diagnosis is clinical based on the characteristic syndrome and temporal relationship to fish ingestion 2, 3.
Do not discharge patients prematurely - symptoms can persist for up to 12 hours and may require repeated antihistamine dosing 2. Patients with cardiovascular involvement may require extended monitoring beyond 24-43 hours 4.
Do not withhold aggressive treatment in severe cases - while most cases are self-limiting, life-threatening hypotension, bronchospasm, and arrhythmias can occur and require the same aggressive management as anaphylaxis 2, 5, 4.
Diagnostic Confirmation
The diagnosis is primarily clinical, but can be confirmed by measuring histamine levels in the implicated fish (>50 mg/100g is diagnostic) or in the patient's plasma 2, 3. However, treatment should never be delayed waiting for laboratory confirmation 2.
Public Health Considerations
Notify state or local health departments of confirmed cases to prevent additional exposures, as the contaminated fish may have been distributed to other consumers 4.