What is the maximum dose of diphenhydramine (antihistamine) for an 11.8 kg child with severe itching?

Maximum Diphenhydramine Dosage for an 11.8 kg Child with Severe Itching

The maximum dose of diphenhydramine for an 11.8 kg child with severe itching is 23.6 mg (1-2 mg/kg, with a maximum of 50 mg per dose). 1

Dosing Guidelines for Diphenhydramine

Weight-Based Dosing

• For children: 1-2 mg/kg per dose 1
• For an 11.8 kg child: 11.8-23.6 mg per dose
• Maximum single dose: 50 mg 1
• Frequency: Every 6 hours as needed 1

Administration Routes

• Oral liquid is preferred over tablets for children as it is more readily absorbed 1
• For severe cases requiring rapid relief, IV administration may be considered at the same dosage 1

Clinical Considerations

Efficacy and Side Effects

• Diphenhydramine is effective for relieving itching and urticaria, but does not relieve respiratory symptoms or shock 1
• Common side effects include:
  • Sedation (most common)
  • Cognitive impairment
  • Psychomotor impairment 1
  • These side effects may contribute to decreased awareness of symptoms 1

Alternative Options

• Consider second-generation H1 antihistamines (such as cetirizine) which have:
  • Less sedation
  • Similar efficacy
  • Fewer adverse effects 2, 3
  • Cetirizine has a relatively rapid onset of action compared to other second-generation antihistamines 4

Important Precautions

Monitoring

• Monitor for excessive sedation, especially after initial doses
• Be aware that diphenhydramine has a higher adverse side-effect profile among children 3
• In rare cases, diphenhydramine can cause drug-induced liver injury, though this is extremely uncommon 5

Duration of Treatment

• For acute allergic reactions, diphenhydramine may be continued for 2-3 days 1
• For chronic itching, reassess after 2-3 days to determine if continued therapy is needed or if alternative treatments should be considered

Treatment Algorithm

1. Start with 1 mg/kg (11.8 mg) for first dose to assess tolerance
2. If inadequate relief and no concerning side effects, increase to 2 mg/kg (23.6 mg) for subsequent doses
3. Administer every 6 hours as needed
4. If symptoms persist beyond 2-3 days, consider:
   • Consulting with an allergist to identify underlying cause
   • Switching to a second-generation antihistamine with less sedation
   • Adding an H2 antihistamine such as ranitidine (1-2 mg/kg) for enhanced effect 1

Remember that while diphenhydramine is effective for treating itching, newer second-generation antihistamines provide similar efficacy with less sedation and may be preferable for ongoing management, especially in children.