What are the recommended antihistamine (anti-histamine) drugs and dosages for treating allergic reactions?

Recommended Antihistamine Drugs and Dosages for Allergic Reactions

Second-generation antihistamines are generally preferred over first-generation antihistamines for treating allergic reactions due to their improved safety profile and reduced sedative effects. 1, 2, 3

Types of Antihistamines

Second-Generation (Non-Sedating) Oral Antihistamines

• Cetirizine: 10 mg once daily for adults and children ≥6 years; 5 mg may be appropriate for less severe symptoms 4, 5
• Fexofenadine: 120 mg once daily 6, 5
• Loratadine: 10 mg once daily 1, 5
• Desloratadine: 5 mg once daily 1, 6

First-Generation (Sedating) Oral Antihistamines

• Diphenhydramine: 25-50 mg every 6 hours (maximum 50 mg per dose) 1
• Should be used with caution due to significant sedation, performance impairment, and anticholinergic effects 1, 3
• May be beneficial when sedation is desired (e.g., sleep induction at bedtime) 1

Intranasal Antihistamines

• Azelastine: Can be used as first-line treatment for allergic and non-allergic rhinitis 1, 5
• Olopatadine: Effective for nasal symptoms of allergic rhinitis 5
• Intranasal antihistamines are equal to or superior to oral second-generation antihistamines for seasonal allergic rhinitis 1
• More effective than oral antihistamines for nasal congestion 1

Treatment Algorithms Based on Condition Severity

For Mild Allergic Reactions (Urticaria, Mild Rhinitis)

• Start with a second-generation oral antihistamine (cetirizine 10 mg, fexofenadine 120 mg, loratadine 10 mg, or desloratadine 5 mg) once daily 2, 5
• For persistent symptoms, can increase dose (up to 4x standard dose for urticaria) 7

For Moderate-to-Severe Allergic Rhinitis

• Intranasal corticosteroids alone or in combination with oral or intranasal antihistamines 2, 5
• Intranasal antihistamines are generally less effective than intranasal corticosteroids but can be used in combination for enhanced effect 1

For Anaphylaxis

• First-line treatment: Epinephrine IM (not antihistamines) 1, 2
• Adjunctive antihistamine therapy:
  • H1 antihistamine: Diphenhydramine 1-2 mg/kg (maximum 50 mg) IV or oral 1
  • Alternative: Second-generation antihistamine for less sedation 1
  • H2 antihistamine: Ranitidine 1-2 mg/kg (maximum 75-150 mg) oral or IV 1

Special Considerations

Pediatric Dosing

• Children ≥6 years: Same as adult dosing for cetirizine (10 mg once daily) 4
• Children <6 years: Consult a doctor for appropriate dosing 4

Elderly Patients

• Adults ≥65 years: Consult a doctor before using cetirizine 4
• Second-generation antihistamines preferred due to reduced anticholinergic effects 3

Patients with Liver or Kidney Disease

• Consult a doctor before using antihistamines 4

Important Cautions

• First-generation antihistamines can cause significant sedation, cognitive impairment, and have been associated with accidents and cardiac events 3
• Intranasal antihistamines can cause systemic absorption and sedation 1
• Oral decongestants (often combined with antihistamines) should be used with caution in patients with cardiovascular disease, hypertension, glaucoma, or hyperthyroidism 1

Adjunctive Therapies

• Saline nasal irrigation is beneficial for chronic rhinorrhea and rhinosinusitis 1
• For allergic rhinitis, allergen avoidance measures should be implemented alongside medication 2
• For persistent symptoms despite optimal antihistamine therapy, consider allergen immunotherapy 2