What is the recommended dose of Benadryl (diphenhydramine) for a 28 kg male?

Benadryl (Diphenhydramine) Dosing for a 28 kg Male

For a 28 kg male, the recommended dose of diphenhydramine is 1 mg/kg, which equals 28 mg, given orally, intramuscularly, or intravenously depending on the clinical indication. 1

Standard Dosing Guidelines

The weight-based dosing for diphenhydramine in pediatric patients is consistently reported as 1 mg/kg per dose across multiple high-quality guidelines 1, 2:

• For this 28 kg patient: 28 mg per dose
• Maximum single dose should not exceed 50 mg 1, 2
• Can be administered every 6 hours as needed 3

Route-Specific Considerations

Oral Administration

• Standard dose: 1 mg/kg (28 mg for this patient) 1
• Liquid formulations are preferred over tablets for more rapid absorption in acute allergic reactions 4

Intravenous/Intramuscular Administration

• Dose range: 1-2 mg/kg 1, 2
• For this patient: 28-56 mg (not to exceed 50 mg maximum) 1, 2
• Critical safety warning: IV diphenhydramine must be administered slowly to avoid hypotension, cardiac toxicity, and other serious adverse effects 3
• When given IV for infusion reactions, administer slowly at 25-50 mg 1

Clinical Context Matters

For Premedication (e.g., before chemotherapy or immunosuppressive therapy)

• Use 1 mg/kg IV or PO 1
• For this 28 kg patient: 28 mg

For Acute Allergic Reactions or Anaphylaxis

• Diphenhydramine is adjunctive therapy only and should never replace epinephrine 1, 4
• Dose: 1-2 mg/kg IV slowly (maximum 50 mg) 1
• For this patient: 28-50 mg IV slowly
• Epinephrine remains the first-line treatment for anaphylaxis 1

For Prevention of Akathisia (with prochlorperazine)

• Dose: 1-2 mg/kg (maximum 50 mg) 2
• For this patient: 28-50 mg

Important Safety Considerations and Caveats

Modern evidence strongly suggests moving away from diphenhydramine when alternatives exist 5, 6:

• Second-generation antihistamines (cetirizine, loratadine, fexofenadine) have superior safety profiles with equal efficacy 4, 5
• Diphenhydramine causes significant sedation, anticholinergic effects, and carries risk of cardiac toxicity in overdose 5, 3, 6
• Some countries (Germany, Sweden) have restricted access to first-generation antihistamines due to safety concerns 6

Adverse Effects to Monitor

• Excessive sedation and impaired psychomotor performance 7, 3
• Anticholinergic effects: dry mouth, blurred vision, urinary retention, constipation 7
• Cardiovascular effects: hypotension (especially with rapid IV administration), tachycardia 7, 3
• Risk of delirium and confusion 7

When to Avoid Diphenhydramine

• Children under 6 years: FDA and AAP recommend against routine use due to 33 deaths associated with diphenhydramine in children under 6 years between 1969-2006 4
• Consider second-generation antihistamines as first-line for routine allergic symptoms 4, 5

Practical Algorithm

1. Determine indication: Is this for acute anaphylaxis, premedication, or routine allergic symptoms?
2. If anaphylaxis: Give epinephrine first, then diphenhydramine 1-2 mg/kg IV slowly (28-50 mg) as adjunct 1
3. If premedication or routine use: Consider second-generation antihistamines first 4, 5
4. If diphenhydramine is chosen: Use 1 mg/kg (28 mg) PO/IM/IV 1
5. Monitor closely for sedation and anticholinergic effects 7, 3