Benadryl (Diphenhydramine) Dosing and Frequency
For adults and children over 12 years, the standard dose is 25-50 mg every 4-6 hours (maximum 6 doses in 24 hours), while children 6-12 years receive 25 mg every 4-6 hours, and diphenhydramine should not be used in children under 6 years. 1
Standard Dosing by Age Group
Adults and Children Over 12 Years
- Dose: 25-50 mg (10-20 mL of liquid formulation) 1
- Frequency: Every 4-6 hours as needed 1
- Maximum: Do not exceed 6 doses in 24 hours 1
Children 6 to Under 12 Years
- Dose: 25 mg (10 mL of liquid formulation) 1
- Frequency: Every 4-6 hours as needed 1
- Maximum: Do not exceed 6 doses in 24 hours 1
Children Under 6 Years
- Do not use diphenhydramine in this age group 1
Specific Clinical Indications with Weight-Based Dosing
Acute Allergic Reactions
- Dose: 1-2 mg/kg per dose (maximum single dose: 50 mg) 2
- Route: IV or oral 2
- Frequency: Every 6 hours for 2-3 days post-discharge 2
- Important consideration: Second-generation non-sedating antihistamines should be strongly considered as alternatives when sedation is problematic 2
Acute Dystonic Reactions
- Dose: 1-2 mg/kg (maximum initial dose: 50 mg) 2, 3
- Route: IV or IM 2
- Frequency: Every 4-6 hours as needed 2
- Alternative: Benztropine 1-2 mg IV/IM if allergic to diphenhydramine 3
Breakthrough Antiemetic (Chemotherapy-Induced)
- Dose: 25-50 mg 3
- Route: PO or IV 3
- Frequency: Every 4-6 hours as needed for dystonic reactions from other antiemetics 3
Pediatric Premedication
- Dose: 1 mg/kg for premedication before agents like thymoglobulin, rituximab, or IVIg 2
Critical Dosing Modifications for Elderly Patients
Patients over 85 years require reduced doses due to heightened anticholinergic sensitivity. 2 The American Geriatrics Society emphasizes increased risks of:
- Cognitive impairment and delirium 2, 4
- Falls and excessive sedation 2, 4
- Urinary retention and constipation 4
Alternative non-sedating antihistamines should be strongly considered instead of diphenhydramine in elderly patients. 2, 4
Important Clinical Pitfalls to Avoid
Do NOT Use for Sleep Disorders
The American Academy of Sleep Medicine explicitly recommends against diphenhydramine for insomnia. 2, 3 Evidence shows:
- Only 8-minute reduction in sleep latency versus placebo 2, 3
- Only 12-minute improvement in total sleep time versus placebo 3
- No improvement in quality of sleep compared to placebo 2, 3
- For elderly insomnia, doxepin 3-6 mg is the recommended alternative 2, 4
Rapid IV Administration Risks
- Rapid IV administration increases risk of cardiac toxicity, hypotension, and may precipitate seizures 3
- Respiratory suppression and paradoxical excitement can occur 3
Toxic Dose Thresholds Requiring Emergency Evaluation
- Children under 6 years: Ingestions of ≥7.5 mg/kg require emergency department referral 5
- Patients 6 years and older: Ingestions of ≥7.5 mg/kg or ≥300 mg (whichever is less) require emergency department referral 5
Adverse Effects Requiring Monitoring
Central Nervous System Effects
- Confusion and delirium, especially in elderly patients 2, 4, 3
- Impaired psychomotor performance 2, 6
- Excessive sedation 4
- Monitor for changes in mental status 4, 3
Anticholinergic Effects
Cardiovascular Effects
Falls Risk Assessment
Assess falls risk, especially in elderly patients, due to sedation and impaired psychomotor function. 4, 3
When to Consider Alternatives
Second-generation antihistamines (cetirizine, fexofenadine, loratadine) provide similar efficacy with significantly less sedation and should be considered first-line for acute allergic reactions when sedation is a concern. 2, 6 These alternatives: