Diphenhydramine Benadryl

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GENERIC NAME: DIPHENHYDRAMINE

BRAND NAME: Benadryl CLASS: Antihistamine; anticholinergic

Mechanism of Action:

Blocks cellular histamine receptors, but does not prevent histamine release; results in decreased capillary permeability and decreased vasodilation, as well as prevention of bronchospasm. Has some anticholinergic effects.

Indications and Field Use:

Anaphylaxis (2nd line) Phenothiazine reactions (extrapyramidal symptoms) Antiemetic

Contraindications:

Known hypersensitivity to diphenhydramine or drugs of similar chemical structure. Newborn or premature infants; nursing mothers. Considerable caution in patients with glaucoma, acute narrow angle; stenosing or obstructive diseases of the GI tract; bronchial asthma; hyperthyroidism; cardiovascular disease or hypertension; age greater than 60 years (all relative benefit vs risk).

Adverse Reactions:

CV: Hypotension; palpitations; arrhythmias; hemolytic anemia. Resp: Anaphylaxis; thickening of bronchial secretions, tightness in chest; wheezing; nasal
stuffiness.
CNS: Sedation; visual disturbances;
seizures.
GU/GI: Urinary frequency or retention; vomiting. Children: In children, may cause paradoxical CNS excitation, seizures, palpitations, thickening of

bronchial secretions.

NOTES ON ADMINISTRATION

Rate of administration: 25 mg or fraction thereof over 1 minute Incompatibilities/Drug Interactions:

Additive effects with alcohol and other CNS depressants (hypnotics, sedatives, tranquilizers, etc.). MAO inhibitors prolong and intensify anticholinergic (drying) effects.

Adult Dosage:

Allergic Reaction: 25-50 mg slow IV push or deep
IM
Anaphylaxis: 25-50 mg slow IV push or deep
IM.
Extrapyramidal symptoms and antiemetic: 10-50 mg IV or deep IM, dose should be individualized according to the needs and patient response.

Pediatric Dosage:

Allergic Reaction: 1.0-1.25 mg/kg slow IV push or deep IM Anaphylaxis or Phenothiazine Overdose: 1-2 mg/kg slow IV push

Routes of Administration:

IV, Deep IM

Onset of Action:

IV 5 - 10 minutes

Peak Effects:

1 hour

Duration of Action:

3-6 hours

Dosage Forms/Packaging:

50 mg/1 ml syringes and vials

Arizona Drug Box Supply:

PARAMEDIC: 50 mg

Special Notes:

*** Not used in newborn or premature infants; used in pregnancy only if clearly needed.

*** In anaphylaxis, used as a 2nd line treatment after epinephrine and steroids. 

© Matt Dillard 2012