What is the recommended treatment for allergic reactions using antihistamines?

Antihistamine Treatment for Allergic Reactions

Second-generation antihistamines are generally preferred over first-generation antihistamines for the treatment of allergic rhinitis due to their lower sedation risk and similar efficacy. 1

First-Line Treatment Options

Oral Antihistamines

• Second-generation antihistamines (preferred):

  • Cetirizine: 10 mg once daily (ages 6 years and older) 2
  • Loratadine: 10 mg once daily
  • Fexofenadine: Age-appropriate dosing
  • Desloratadine: Age-appropriate dosing

• First-generation antihistamines (use with caution):

  • Diphenhydramine: 25-50 mg every 6 hours (1-2 mg/kg per dose, maximum 50 mg) 3
  • Note: These have significant potential to cause sedation, performance impairment, and anticholinergic effects 1

Intranasal Antihistamines

• May be considered as first-line treatment for allergic and nonallergic rhinitis 1
• Equal to or superior to oral second-generation antihistamines for seasonal allergic rhinitis 1
• Generally less effective than intranasal corticosteroids 1
• Note: Can cause sedation in some patients and may have a bitter taste 1

Treatment Algorithm Based on Symptom Severity

For Mild Allergic Rhinitis Symptoms

1. Start with a second-generation oral antihistamine (cetirizine, loratadine, fexofenadine)
2. If inadequate response, consider:
   • Switching to another second-generation antihistamine
   • Adding intranasal antihistamine
   • Adding intranasal corticosteroid

For Moderate to Severe Allergic Rhinitis

1. Intranasal corticosteroids are typically most effective for controlling sneezing, itching, rhinorrhea, and nasal congestion 1
2. Can be combined with oral antihistamines for enhanced symptom control

For Nasal Congestion

• Oral decongestants (pseudoephedrine, phenylephrine) can reduce nasal congestion 1
• Use with caution in patients with hypertension, cardiac arrhythmia, glaucoma, or hyperthyroidism 1
• Topical decongestants should be limited to short-term use (≤3 days) to avoid rhinitis medicamentosa 1

For Rhinorrhea

• Intranasal anticholinergics (ipratropium bromide) effectively reduce rhinorrhea 1
• Can be combined with intranasal corticosteroids for enhanced effect 1

Special Considerations for Allergic Reactions

For Anaphylaxis or Severe Allergic Reactions

1. Epinephrine is the first-line treatment (0.01 mg/kg) 1, 3
   • 0.15 mg auto-injector for children weighing 7.5-25 kg
   • 0.3 mg auto-injector for children over 25 kg and adults
2. Antihistamines are adjunctive therapy and should not replace epinephrine 1

For Urticaria (Hives)

• Second-generation antihistamines are first-line treatment
• For difficult-to-treat cases, increasing the dose up to 4-fold may improve symptoms without compromising safety 4
• H1 and H2 antihistamine combination may be more effective than either alone 3

Important Clinical Caveats

• Antihistamines primarily relieve itching, sneezing, and rhinorrhea but have limited effect on nasal congestion 1
• Continuous treatment is more effective than intermittent use for seasonal or perennial allergic rhinitis 1
• When prescribing first-generation antihistamines, ensure patients understand the potential for adverse effects and the availability of alternatives with fewer side effects 1
• Antihistamines should be discontinued before allergy testing to avoid false-negative results 1
• Avoid performing allergy testing without clinical suspicion of a specific trigger 3

By following this evidence-based approach to antihistamine selection and administration, clinicians can effectively manage allergic reactions while minimizing adverse effects and optimizing patient outcomes.