What are the names and dosages of H1 antihistamines (histamine 1 receptor antagonists) used to treat urticarial rash in infants?

H1 Antihistamines for Urticarial Rash in Infants: Names and Dosing

For urticarial rash in infants, first-line H1 antihistamines include cetirizine (0.25 mg/kg/day), loratadine (0.2 mg/kg/day), and diphenhydramine (1-2 mg/kg/dose every 6 hours) with dosing adjusted for age and weight. 1

First-Generation H1 Antihistamines

First-generation antihistamines are effective but have significant sedative effects:

1. Diphenhydramine (Benadryl)

   • Dosing: 1-2 mg/kg/dose every 6 hours
   • Available as: 12.5 mg/5 mL liquid
   • Age: Approved for children ≥2 years, but commonly used in infants under physician supervision
   • Note: Significant sedation; use with caution

2. Chlorpheniramine (Chlor-Trimeton)

   • Dosing: 0.35 mg/kg/day divided every 6-8 hours
   • Available as: 2 mg/5 mL liquid
   • Age: Approved for children ≥2 years
   • Note: Moderate sedation

3. Hydroxyzine (Atarax)

   • Dosing: 0.5-1 mg/kg/dose every 6 hours
   • Available as: 10 mg/5 mL liquid
   • Age: All ages with physician supervision
   • Note: Significant sedation; often used at bedtime

Second-Generation H1 Antihistamines

These are preferred due to less sedation and longer duration of action:

1. Cetirizine (Zyrtec)

   • Dosing: 0.25 mg/kg/day once daily
   • Available as: 5 mg/5 mL liquid
   • Age: Approved for infants ≥6 months
   • Note: Minimal sedation, once-daily dosing

2. Loratadine (Claritin)

   • Dosing: 0.2 mg/kg/day once daily
   • Available as: 5 mg/5 mL liquid
   • Age: Approved for children ≥2 years, but often used in infants under physician supervision
   • Note: Non-sedating, once-daily dosing

3. Fexofenadine (Allegra)

   • Dosing: 2 mg/kg/day divided twice daily
   • Available as: 30 mg/5 mL suspension
   • Age: Approved for children ≥6 months
   • Note: Non-sedating

Treatment Algorithm for Urticarial Rash in Infants

1. Initial Assessment

   • Determine severity of urticaria (mild localized vs. extensive)
   • Rule out anaphylaxis (if present, epinephrine is first-line)

2. First-Line Treatment

   • For mild-moderate urticaria: Second-generation H1 antihistamine
     • Cetirizine preferred due to established safety in infants ≥6 months
     • Loratadine as alternative

3. If Inadequate Response

   • Increase dose of second-generation antihistamine (within safe limits)
   • Consider adding H2 antihistamine (ranitidine) as adjunctive therapy

4. For Severe/Nighttime Symptoms

   • Consider first-generation antihistamine (diphenhydramine) at bedtime
   • Monitor closely for adverse effects

Important Clinical Considerations

• Second-generation antihistamines are preferred over first-generation due to better safety profile, minimal cognitive effects, and longer duration of action 2

• Sedating antihistamines should be limited to situations where sedation is beneficial (severe nighttime symptoms) 3

• Duration of treatment should typically be 2-3 days for acute urticaria, with follow-up if symptoms persist 1

• Caution in special populations:

  • Renal impairment: Avoid or reduce dose of cetirizine
  • Hepatic impairment: Use caution with chlorpheniramine and hydroxyzine 1

• Monitoring: Watch for paradoxical reactions, particularly excitation in young children with first-generation antihistamines

• Epinephrine, not antihistamines, remains the first-line treatment for anaphylaxis; antihistamines are adjunctive only 1

Remember that antihistamines primarily relieve itching and urticaria but do not treat underlying causes or prevent progression to anaphylaxis. Always reassess if symptoms worsen or fail to improve within 24-48 hours.