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Diphenhydramine (Benadryl)

Diphenhydramine Hydrochloride




    Adult: 25-50 mg IV or 50 mg deep IM.
    The patient may require as much as 100 mg.
    Do not exceed 400 mg per day.

    Pediatric:1 mg/kg (maximum 50 mg).
    (Dilute with 9 ml NS to Equal 50 mg / 10 ml).
    Not to exceed 300 mg per day.


    Diphenhydramine is an antihistamine with anticholinergic (drying) and sedative side effects. Antihistamines appear to compete with histamine for cell receptor sites on effector cells. Diphenhydramine prevents, but does not reverse histamine mediated responses, particularly histamine effects on the smooth muscle of the bronchial airways, gastrointestinal tract, uterus, and blood vessels.


    - Allergy symptoms, anaphylaxis (as an adjunct to epinephrine).
    - Sedation of violent patient after giving Haldol IM.
    - Dystonic reactions from phenothiazine overdose (e.g. Haldol, Compazine, Thorazine, and Stelazine).
    - Rhinitis.
    - Anti-parkinsonism.
    - Nighttime sedation.
    - Motion sickness.


    Diphenhydramine is not to be used in newborn or premature infants or in nursing mothers. Diphendramine is also not to be used in patients with lower respiratory tract symptoms including asthma.


    In infants and children especially, antihistamines in overdose may cause hallucinations,convulsions, or death.
    As in adults, antihistamines may diminish mental alertness in children.
    In young children, they may produce excitation.
    Diphenhydramine has additive effects with alcohol and other CNS depressants(hyptonics, sedatives, tranquilizers, etc.)
    Antihistamines are more likely to cause dizziness, sedation, and hypotension in the elderly (60 years or older) patient.


    CNS:Drowsiness, confusion, insomnia, headache, vertigo (all especially in the elderly).

    Cardiovascular:Palpitations, tachycardia, PVC's and hypotension.

    Respiratory:Thickening of bronchial secretions, tightness of the chest, wheezing, nasal stuffiness.

    GI:Nausea, vomiting, diarrhea, dry mouth, and constipation.

    GU:Dysuria, urinary retention.

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