What is the treatment plan for a patient presenting to urgent care with a mild to moderate allergic reaction?

Treatment Plan for Mild to Moderate Allergic Reaction in Urgent Care

Immediate Assessment and Risk Stratification

For mild to moderate allergic reactions presenting to urgent care, immediately assess whether the reaction meets criteria for anaphylaxis, as this fundamentally changes management. 1, 2

• If the patient has multi-system involvement (skin + respiratory, skin + cardiovascular, or skin + gastrointestinal symptoms), treat as anaphylaxis with immediate intramuscular epinephrine 3, 1
• If symptoms are isolated to skin only (urticaria, flushing, mild angioedema without airway involvement), proceed with antihistamine-based treatment 3, 2
• Critical pitfall: The most common error is using antihistamines when epinephrine is indicated, which significantly increases risk of progression to life-threatening reaction 3

Treatment Algorithm for True Mild/Moderate Reactions (Skin-Only Symptoms)

First-Line Pharmacologic Management

Administer H1 antihistamine as primary treatment for isolated cutaneous symptoms:

• Diphenhydramine 25-50 mg orally or IV (1-2 mg/kg in children, maximum 50 mg) 3, 2
• Alternative: Cetirizine 10 mg orally for less sedation with comparable onset 3
• Add H2 antihistamine for enhanced effect: Ranitidine 75-150 mg orally or IV (1-2 mg/kg in children) 3, 2

Adjunctive Therapies

• Consider corticosteroids to prevent biphasic reactions: Prednisone 0.5-1 mg/kg orally (maximum 60-80 mg) or methylprednisolone IV 3, 2
• Corticosteroids have no acute benefit but may reduce risk of symptom recurrence over 4-72 hours 3

Mandatory Observation Period

Observe all patients for minimum 4-6 hours after symptom resolution, monitoring specifically for:

• Progression to respiratory symptoms (wheezing, stridor, throat tightness) 3, 1
• Development of hypotension or cardiovascular symptoms 1
• Recurrence of skin symptoms suggesting biphasic reaction 3, 2
• If any progression occurs during observation, immediately administer IM epinephrine 0.3-0.5 mg (0.01 mg/kg in children, max 0.5 mg) into anterolateral thigh 3, 4

Critical Decision Point: When to Give Epinephrine Despite "Mild" Presentation

Administer epinephrine immediately even for seemingly mild symptoms if:

• Patient has history of prior severe allergic reaction to the same trigger 3
• Patient has coexisting asthma (higher risk for severe progression) 1, 5
• Any respiratory symptoms develop (even mild throat clearing or cough) 3, 1
• Any gastrointestinal symptoms appear (nausea, vomiting, cramping) 1, 2
• Symptoms progress or fail to improve with antihistamines within 15-30 minutes 2

The threshold for epinephrine should be low—there are no absolute contraindications to epinephrine in allergic reactions, and the risk of death from untreated anaphylaxis outweighs any medication risks 3, 4

Discharge Planning and Prevention

Medications to Send Home

Prescribe 2-3 day course of:

• Diphenhydramine 25-50 mg every 6 hours 3
• H2 antihistamine (ranitidine) twice daily 3
• Prednisone daily 3

Epinephrine Auto-Injector Prescription

Prescribe epinephrine auto-injector if:

• Reaction involved any respiratory or cardiovascular symptoms 3, 1
• Patient has history of severe reactions 1
• Trigger is unavoidable (food allergy, insect venom) 3, 1
• Dosing: 0.15 mg for patients 10-25 kg; 0.3 mg for patients >25 kg 3, 4
• Provide hands-on training with trainer device before discharge 1

Mandatory Follow-Up

• Refer to allergist-immunologist within 1-2 weeks for trigger identification and long-term management 3, 1
• Provide written emergency action plan 3, 1
• Educate on strict allergen avoidance 3
• Recommend medical identification jewelry 3

Special Considerations

For patients on beta-blockers: Epinephrine may be less effective; glucagon 1-2 mg IV may be needed as rescue medication if epinephrine fails 3

For pregnant patients: Epinephrine is safe and indicated—maternal hypoxia poses greater fetal risk than epinephrine 4

Common pitfall to avoid: Never substitute albuterol inhaler for epinephrine in respiratory symptoms—albuterol only treats bronchospasm, not upper airway edema or shock 3