Diphenhydramine Dosage and Administration

Adult Dosing

The standard oral/parenteral dose of diphenhydramine for adults is 25-50 mg per dose, as recommended by the American Academy of Allergy, Asthma, and Immunology 1, 2
For sedation as an adjunct in procedures, the recommended dose is 25-50 mg intravenously, according to the American Gastroenterological Association 3, 4
For allergic reactions, the recommended dose is 25-50 mg parenterally, as suggested by the American Academy of Allergy, Asthma, and Immunology 5, 6
For discharge therapy after allergic reactions, diphenhydramine is recommended every 6 hours for 2-3 days, according to the American Academy of Allergy, Asthma, and Immunology 5, 6

The weight-based dosing for children is 1-2 mg/kg per dose, as recommended by the American Academy of Allergy, Asthma, and Immunology 1, 2
The maximum single dose for children is 50 mg, according to the American Academy of Allergy, Asthma, and Immunology 5, 7

For anaphylaxis, parenteral administration is preferred for faster onset of action, as recommended by the American Academy of Allergy, Asthma, and Immunology 1
Intravenous administration should be slow to minimize adverse effects, according to the American Gastroenterological Association 4

The onset of action of diphenhydramine is several minutes when given intravenously, and the duration of effect is 4-6 hours, as reported by the American Gastroenterological Association 4
In anaphylaxis management, diphenhydramine is considered second-line therapy to epinephrine and should never be administered alone, as recommended by the American Academy of Allergy, Asthma, and Immunology 1
When used as an adjunct for sedation, diphenhydramine may allow for reduction in doses of other sedatives, according to the American Gastroenterological Association 3, 4
Hypnotic effects are increased when combined with alcohol, benzodiazepines, or opioid narcotics, as reported by the American Gastroenterological Association 4

Common adverse effects of diphenhydramine include dizziness, blurred vision, dry mouth, hypotension, epigastric discomfort, urinary retention, and wheezing, as reported by the American Gastroenterological Association 4