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Diphenhydramine
Trade Name
Benadryl
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Diphenhydramine
Class
- Antihistamine
- Anticholinergic
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Diphenhydramine
Mechanism of Action
- Blocks cellular histamine receptors
- Decreases vasodilation
- Decreases motion sickness
- Reverses extrapyramidal reactions
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Diphenhydramine
Indications
- Symptomatic relief of allergies
- Allergic reactions
- Anaphylaxis
- Acute dystonic reactions (phenothiazines).
- Blood administration reactions
- Motion sickness
- Hay fever
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Diphenhydramine
Contraindications
- Asthma
- Glaucoma/Narrow Angle Glaucoma
- Pregnancy
- Hypertension
- Infants
- Patients taking Monoamine Oxidase Inhibitors
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Diphenhydramine
Adverse Reactions
- Sedation
- Hypotension
- Seizures
- Visual disturbances
- Vomiting
- Urinary retention
- Palpitations
- Dysrhythmias
- Dry mouth and throat
- Paradoxical CNS excitation in children
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Diphenhydramine
Drug Interactions
- Potentiates effects of alcohol and other anticholinergics
- May inhibit corticosteroid activity
- MAOIs prolong anticholinergic effects of diphenhydramine
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Diphenhydramine
How Supplied
- Tablet: 25, 50 mg
- Capsules: 25, 50 mg
- 50 or 100 mg prefilled syringes or vials (IV or IM)
- 12.5 mg/5 ml elixir
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Diphenhydramine
Dosage and Administration
Adult
25 -50 mg IM or IV or P.O.
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Diphenhydramine
Dosage and Administration
Pediatric
- 1-2 mg/kg IV, IO slowly or IM
- If given PO: 5 mg./kg./ 24 hours
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Diphenhydramine
Duration of Action
- Onset: 15-30 minutes
- Peak effect: 1 hour
- Duration: 3-12 hours
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Diphenhydramine
Special Considerations
- Pregnancy safety: Category B
- Not used in infants or in pregnancy (Category B).
- If used in anaphylaxis, will be in conjunction with epinephrine, steroids.
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