How should allergic reactions be managed in primary care, including mild, moderate, and severe presentations?

Treatment of Allergic Reactions in Primary Care

For severe allergic reactions (anaphylaxis), immediately administer intramuscular epinephrine 0.01 mg/kg (maximum 0.5 mg) into the anterolateral thigh, then transfer to emergency facility—there are no absolute contraindications to epinephrine in anaphylaxis. 1, 2

Severity-Based Treatment Algorithm

Severe Reactions (Anaphylaxis)

Recognize anaphylaxis when you see:

• Acute onset with skin/mucosal involvement (hives, flushing, lip swelling) PLUS respiratory compromise (wheezing, stridor, dyspnea) OR hypotension/syncope
• Acute hypotension or bronchospasm alone after known allergen exposure
• Severe skin findings: vesicles, dusky lesions, painful skin, mucosal hemorrhage, or skin detachment 3

Immediate actions:

1. Epinephrine IM first-line (anterolateral thigh):

   • 10-25 kg: 0.15 mg autoinjector

   • 25 kg: 0.3 mg autoinjector

   • Alternative: 0.01 mg/kg of 1:1,000 solution (max 0.5 mg)
   • Repeat every 5-15 minutes if needed 1

2. Position patient recumbent with legs elevated (if tolerated) 1

3. Adjunctive treatments (do not delay epinephrine):

   • Albuterol nebulizer (1.5 mL child, 3 mL adult) for bronchospasm
   • IV fluid bolus if hypotensive or orthostatic
   • Supplemental oxygen 1

4. Transfer to emergency department for 4-6 hour observation (longer if severe) 2

Critical pitfall: Using antihistamines instead of epinephrine is the most common reason for not administering epinephrine and significantly increases risk of life-threatening progression 1. The evidence clearly shows that risk of death from anaphylaxis outweighs any theoretical epinephrine risks, even in patients with cardiovascular disease or on MAOIs 2.

Mild-to-Moderate Reactions

For isolated symptoms like flushing, urticaria, mild angioedema, or oral allergy syndrome without respiratory/cardiovascular involvement:

1. H1 antihistamine: Diphenhydramine 1-2 mg/kg (max 50 mg) oral or IV 1

   • Alternative: non-sedating second-generation antihistamine

2. H2 antihistamine: Consider adding ranitidine 1

3. Mandatory close observation for progression to anaphylaxis—if any worsening occurs, immediately give epinephrine 1, 2

Exception: If patient has history of prior severe reaction, give epinephrine promptly even for mild initial symptoms 1, 2

Post-Acute Management

After successful treatment of anaphylaxis, prescribe at discharge:

• Epinephrine autoinjector with hands-on training 2
• Adjunctive medications for 2-3 days:
  • H1 antihistamine (diphenhydramine every 6 hours or non-sedating alternative)
  • H2 antihistamine (ranitidine twice daily)
  • Corticosteroid (prednisone daily) 1, 2, 1

Note on corticosteroids: While commonly recommended to prevent biphasic reactions, little data actually support their effectiveness for this purpose 1. Recent evidence even suggests supplemental corticosteroids with epinephrine may result in worse outcomes 4. However, guidelines still recommend their use post-discharge.

Essential Patient Education

Provide written anaphylaxis emergency action plan covering:

• Allergen avoidance strategies
• Early symptom recognition
• When and how to use epinephrine autoinjector
• Call 911 after epinephrine administration
• Medical identification jewelry 2

Follow-Up and Referral

• Mandatory follow-up with primary care within days
• Refer to allergist/immunologist for:
  • Identification of specific allergen triggers
  • Consideration of immunotherapy if appropriate
  • Development of long-term management plan 2

Key distinction: Most mild-to-moderate allergic symptoms (urticaria, mild angioedema, allergic rhinitis) can be successfully managed in primary care with antihistamines and observation 5. However, any patient experiencing anaphylaxis requires emergency treatment, hospital observation, specialist referral, and lifelong epinephrine autoinjector access 6, 7.