What is the recommended dosage of diphenhydramine (antihistamine) for itching?

Diphenhydramine Dosing for Itching (Pruritus)

For adults with itching, diphenhydramine should be dosed at 25-50 mg orally or IV every 6 hours as needed, with a maximum single dose of 50 mg. 1

Standard Adult Dosing

• Oral or IV administration: 25-50 mg every 6 hours as needed 1
• Maximum single dose is 50 mg 1
• This dosing applies to both acute allergic reactions with pruritus and dermatologic conditions causing itching 1

Pediatric Dosing

For children, the weight-based dose is 1-2 mg/kg per dose, with a maximum of 50 mg per single dose. 1

• Administer every 6 hours as needed 1
• Oral liquid formulations are more readily absorbed than tablets in children 1

Important Clinical Considerations

Efficacy Limitations

• Diphenhydramine is only effective for relieving itching and urticaria—it does not treat systemic symptoms like respiratory distress, hypotension, or gastrointestinal symptoms 1
• For pruritus specifically, diphenhydramine is more effective than H2-antihistamines (like cimetidine) when used alone 2

Sedation and Safety Concerns

• First-generation antihistamines like diphenhydramine cause significant sedation, cognitive impairment, and psychomotor dysfunction 1
• These sedating effects may decrease awareness of worsening allergic symptoms 1
• Consider second-generation antihistamines (cetirizine 10 mg) as an alternative for patients where sedation is problematic, though onset may be slightly slower 1

Special Populations

Elderly patients require dose reduction and careful monitoring: 3

• Increased risk of confusion, delirium, falls, and anticholinergic side effects 3
• Monitor for mental status changes, urinary retention, and constipation 3
• Consider non-sedating antihistamines or topical treatments as safer alternatives in elderly patients 3

Duration of Therapy

• For post-discharge management after allergic reactions: continue every 6 hours for 2-3 days 1
• Can be combined with H2-antihistamines (ranitidine) for enhanced effect in urticaria, though benefit for isolated pruritus is less clear 1, 2

Alternative Considerations

• Hydroxyzine 10 mg every 6 hours is an alternative first-generation antihistamine for itching 1
• For chronic urticaria refractory to antihistamines, higher doses of non-sedating antihistamines (up to 4-6 times the standard dose) are more appropriate than continuing diphenhydramine 1, 4
• Topical diphenhydramine should be used with extreme caution due to risk of systemic absorption and toxicity, particularly in children 5