GD-038-PHS-EMS: Drug Profile for Diphenhydramine HCl
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GENERIC NAME: DIPHENHYDRAMINE HCl
112.10
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
Incompatibilities/Drug Interactions:
Additive effects with alcohol and other CNS depressants (hypnotics, sedatives,
tranquilizers, etc.).
MAO inhibitors prolong and intensify anticholinergic (drying) effects.
