Diphenhydramine for Severe Dermatitis

Clinical Context and Efficacy

The American Academy of Allergy, Asthma, and Immunology recommends diphenhydramine as an adjunctive therapy to relieve itching and urticaria in severe dermatitis, but it does not address other systemic manifestations of severe allergic reactions 1
Diphenhydramine provides symptomatic relief of pruritus but does not treat the underlying inflammatory process 1
Combining diphenhydramine with an H2-antagonist, such as ranitidine, provides superior control of urticaria compared to diphenhydramine alone, according to the European Academy of Allergy and Clinical Immunology 4, 2

The onset of action of diphenhydramine occurs within several minutes when given parenterally, with a duration of effect of 4-6 hours, according to the American Academy of Allergy, Asthma, and Immunology 2, 3
Repeat dosing of diphenhydramine may be necessary every 6 hours for ongoing symptoms, not exceeding 400 mg/24 hours, as recommended by the American Academy of Allergy, Asthma, and Immunology 3, 2

The American Academy of Allergy, Asthma, and Immunology advises against using diphenhydramine as monotherapy if anaphylaxis is suspected, and recommends epinephrine 0.3-0.5 mg IM as first-line treatment 3, 1, 2
Common adverse effects of diphenhydramine include sedation, dizziness, blurred vision, dry mouth, hypotension, and urinary retention, according to the American Academy of Allergy, Asthma, and Immunology 2

The American Academy of Allergy, Asthma, and Immunology recommends immediate escalation of treatment if severe dermatitis is accompanied by respiratory symptoms, hypotension, or extensive body surface area involvement, and advises adding epinephrine, albuterol, or systemic corticosteroids as needed 3, 1, 4