Benadryl (Diphenhydramine) Syrup Dosing
For allergic reactions, diphenhydramine syrup should be dosed at 25-50 mg (10-20 mL) for adults and children over 12 years, and 25 mg (10 mL) for children 6-12 years, every 4-6 hours as needed, not exceeding 6 doses in 24 hours; however, for insomnia, diphenhydramine should not be used as it lacks clinically significant efficacy. 1, 2
Dosing for Allergic Reactions
Standard Dosing (FDA-Approved)
- Adults and children over 12 years: 25-50 mg (10-20 mL) every 4-6 hours 1
- Children 6 to under 12 years: 25 mg (10 mL) every 4-6 hours 1
- Children under 6 years: Do not use 1
- Maximum: Do not exceed 6 doses in 24 hours 1
Role in Anaphylaxis Management
Diphenhydramine is only adjunctive therapy in anaphylaxis—epinephrine is first-line treatment and must never be substituted. 2
- Diphenhydramine relieves only itching and urticaria 2
- It does NOT relieve stridor, shortness of breath, wheezing, GI symptoms, or shock 2
- Standard adult dose for anaphylaxis: 25-50 mg oral or IV 2
- Sedation and cognitive impairment are recognized side effects that may decrease awareness of anaphylaxis symptoms 2
Alternative Considerations for Allergic Reactions
Consider second-generation antihistamines like cetirizine 10 mg when sedation is a concern, as it has rapid onset comparable to diphenhydramine but causes less sedation. 2, 3
- Cetirizine has the fastest onset among newer antihistamines 3
- Fexofenadine causes no psychomotor or cognitive impairment but has slower onset 3
- The small additional cost ($0.52-2.39 per dose) is outweighed by reduced sedation risk 3
Insomnia: Not Recommended
The American Academy of Sleep Medicine recommends against using diphenhydramine for insomnia in adults. 2
Evidence Against Use for Insomnia
- Diphenhydramine 50 mg showed no clinically significant improvement in sleep latency or total sleep time versus placebo 2
- Benefits do not outweigh harms 2
- Complete tolerance to sedative effects develops within 3 days of regular use, making it ineffective for ongoing insomnia 4
- For insomnia, consider doxepin 3-6 mg or other evidence-based alternatives instead 5
Special Population: Elderly Patients
Elderly patients, especially those over 85 years, should receive reduced doses or avoid diphenhydramine entirely due to increased anticholinergic sensitivity. 5
Risks in Elderly
- Increased risk of confusion, delirium, and cognitive impairment 5
- Higher fall risk due to sedation 5
- Anticholinergic effects: dry mouth, blurred vision, urinary retention, constipation 5
- Cardiovascular effects: hypotension and tachycardia 5
Monitoring Requirements
- Monitor for changes in mental status or excessive sedation 5
- Assess fall risk 5
- Monitor for urinary retention and constipation 5
Alternatives for Elderly
- For pruritus: topical treatments or non-sedating antihistamines 5
- For allergic reactions: cetirizine or fexofenadine when appropriate 2, 3
Important Safety Considerations
Cognitive and Psychomotor Impairment
Diphenhydramine significantly impairs psychomotor performance and cognitive function, particularly on day 1 of use. 6, 4
- Reduces reaction time and vigilance 6
- Increases daytime sleepiness 6
- Impairment is most pronounced with initial doses but tolerance develops rapidly 4
Rapid IV Administration Risks
When given intravenously, diphenhydramine must be administered slowly to avoid potentially life-threatening adverse effects. 7
- Rapid IV administration can cause serious toxicity 7
- Adverse effects are more likely with large or excessive doses 7
Clinical Pitfalls to Avoid
- Never substitute diphenhydramine for epinephrine in anaphylaxis 2
- Do not use for chronic insomnia—tolerance develops within 3 days 4, 2
- Avoid in elderly patients when possible due to anticholinergic burden 5
- Do not exceed maximum daily dosing (6 doses per 24 hours) 1
- Consider non-sedating alternatives when sedation could impair function or safety 3