What is the recommended dose of Benadryl (diphenhydramine) for treating hives in adults and children?

Benadryl (Diphenhydramine) Dosing for Hives

For adults with hives, diphenhydramine should be administered at 25-50 mg orally every 4-6 hours as needed, with a maximum of 300 mg in 24 hours. For children 6-12 years old, the recommended dose is 25 mg (10 mL) every 4-6 hours, while diphenhydramine should not be used in children under 6 years of age. 1

Adult Dosing

• Standard dose: 25-50 mg (10-20 mL) orally every 4-6 hours
• Maximum daily dose: No more than 6 doses (300 mg) in 24 hours
• Duration of treatment: As needed for symptom control

Pediatric Dosing

• Children 6-12 years: 25 mg (10 mL) every 4-6 hours
• Children >12 years: Same as adult dosing (25-50 mg every 4-6 hours)
• Children <6 years: Not recommended 1

Administration Considerations

Diphenhydramine can be administered in several ways for hives:

• Oral route is most common for outpatient management
• Intramuscular route may be considered in acute settings when rapid response is needed, though evidence suggests the onset of action advantage over newer antihistamines is not statistically significant 2
• Intravenous route should be reserved for severe cases in emergency settings

Efficacy and Alternatives

While diphenhydramine is effective for acute urticaria, newer second-generation antihistamines may offer advantages:

• Recent research shows intravenous cetirizine (10 mg) is non-inferior to intravenous diphenhydramine (50 mg) for acute urticaria with benefits of less sedation, fewer adverse events, and shorter treatment time 3
• For chronic urticaria, non-sedating second-generation antihistamines like cetirizine, desloratadine, levocetirizine, and rupatadine are recommended as first-line treatments 4

Important Side Effects and Precautions

• Sedation: Diphenhydramine commonly causes drowsiness and can impair cognitive and motor function
• Anticholinergic effects: Dry mouth, blurred vision, urinary retention, constipation
• Special populations:
  • Hepatic impairment: Should be avoided in severe liver disease due to sedating effects 5
  • Pregnancy: Best to avoid all antihistamines especially in first trimester; chlorphenamine is often chosen if antihistamine therapy is necessary due to its long safety record 5

Management Algorithm for Hives

1. For mild to moderate acute hives:

   • Start with diphenhydramine 25-50 mg orally every 4-6 hours (adults)
   • Consider adding H2 antagonists for better symptom control 6

2. For severe or persistent hives:

   • Consider higher dose of diphenhydramine (up to 50 mg per dose)
   • If inadequate response, consider switching to second-generation antihistamines
   • For refractory cases, consider short course of oral corticosteroids 5

3. For anaphylaxis with hives:

   • Epinephrine is first-line treatment (0.01 mg/kg, max 0.5 mg IM)
   • Diphenhydramine should be used as adjunctive therapy (25-50 mg) for cutaneous symptoms only 7
   • Never delay epinephrine to administer antihistamines 7

Remember that while diphenhydramine is effective for acute hives, its sedating properties may limit its use, especially for daytime treatment or in patients who need to remain alert. Consider non-sedating alternatives for long-term management of chronic urticaria.