What is the daily maximum dose of Benadryl (diphenhydramine)?

Maximum Daily Dose of Diphenhydramine (Benadryl)

The maximum daily dose of diphenhydramine (Benadryl) for adults is 400 mg per day, administered in divided doses. 1

Dosing Guidelines by Age Group

Adults:

• Standard single dose: 25-50 mg
• Maximum single dose: 50 mg
• Dosing frequency: Every 4-6 hours as needed
• Maximum daily dose: 400 mg 1
• Administration rate (IV): Not exceeding 25 mg/min

Children (excluding premature infants and neonates):

• Dosing based on weight: 5 mg/kg/24 hr
• Alternative dosing based on body surface area: 150 mg/m²/24 hr
• Maximum daily dose: 300 mg
• Divided into four doses throughout the day 1

Administration Routes

Diphenhydramine is available in multiple formulations:

• Oral tablets: 25 mg, 50 mg
• Oral liquid: 12.5 mg/5 mL
• Injectable: For IV or IM use when oral route is impractical

Clinical Considerations

Safety Concerns

• Diphenhydramine has significant sedative properties that can impair driving ability and cognitive function 2
• Risk of toxicity in overdose includes cardiac arrhythmias, seizures, hyperpyrexia, and coma 3
• Recent social media challenges have led to dangerous misuse of diphenhydramine with fatal outcomes in adolescents 4

Special Populations

• Elderly patients may be more sensitive to anticholinergic effects and should generally receive lower doses
• Patients with hepatic impairment may require dose adjustment due to reduced metabolism
• Use with caution in patients with narrow-angle glaucoma, prostatic hypertrophy, or urinary retention

Alternative Considerations

Many experts now recommend second or third-generation antihistamines over diphenhydramine due to:

• Fewer sedative effects
• Longer duration of action
• Better safety profile
• Similar efficacy for allergic conditions 5

Common Uses in Clinical Practice

1. Allergic reactions (as adjunctive therapy)

   • For anaphylaxis: 1-2 mg/kg/dose (maximum 50 mg) 6
   • Used alongside epinephrine (not as monotherapy)

2. Acute management of agitation

   • Adolescents: 25-50 mg per dose 6
   • Can be used in combination with antipsychotics

Important Cautions

• Never use diphenhydramine as first-line treatment for anaphylaxis (epinephrine is first-line)
• Avoid in patients taking MAO inhibitors
• Monitor for paradoxical excitation, especially in children
• Significant drug-drug interactions with other CNS depressants

Remember that while diphenhydramine is widely available over-the-counter, it carries significant risks at higher doses and should be used with appropriate caution.