diphenhydramine hydrochloride (Benadryl)

Question 1

diphenhydramine hydrochloride (Benadryl)
Class

Answer 1

antihistamine

Question 2

diphenhydramine hydrochloride (Benadryl)
Pharmacology and action

Answer 2

Blocks H1 receptors in the respiratory tract, blood vessels, and GI smooth
muscle. Reverses extrapyramidal reactions.

Question 3

diphenhydramine hydrochloride (Benadryl)
Onset, duration, peak effect

Answer 3

Onset: 10-15 minutes Duration: 6-8 hours Peak Effect: 1 hour

Question 4

diphenhydramine hydrochloride (Benadryl)
Indications and contraindications

Answer 4

Indications
● Symptomatic allergic reaction
● Adjunct to epinephrine in anaphylaxis
● Dystonic/extrapyramidal symptoms secondary to phenothiazines
● Nausea/vomiting
● Chemical restraint
IV. Contraindications
● Newborns and premature infants
● Late stage pregnancy
● Breastfeeding mothers
● Asthma
● Narrow-angle glaucoma
● Benign prostatic hypertrophy
● Alcohol intoxication

Question 5

diphenhydramine hydrochloride (Benadryl)
adverse reactions and side effects

Answer 5

Note: Hallucinations, confusion, and paradoxical CNS excitation can occur in children.
Cardiovascular: Dysrhythmias, palpitations, hypotension
Neurological: Seizures, dizziness, headache, blurred vision
Respiratory: wheezing, thickening of bronchial secretions

Question 6

diphenhydramine hydrochloride (Benadryl)
special considerations

Answer 6

● Pregnancy Safety: Category B
● Increases effectiveness of epinephrine
● Can be given with any H2-blocking antihistamine

Question 7

diphenhydramine hydrochloride (Benadryl)
dosage

Answer 7

Adult
Allergic reaction, anaphylaxis: 1mg/kg IV/IM/PO. Maximum dose: 50mg
Nausea/vomiting: 12.5-25mg IV/IM/PO
Dystonic reaction/extrapyramidal symptoms: 25-50mg IV/IM.
Pediatric
Allergic reaction, anaphylaxis: 1mg/kg IV/IM/PO. Maximum dose: 50mg
Nausea/vomiting: >2 years and weight greater than 12kg: 0.1mg/kg IV.
Maximum dose: 25mg.
Dystonic reaction/extrapyramidal symptoms: 1-1.25mg/kg IV/IO/IM. Maximum single dose:
25mg.
Chemical restraint: 1mg/kg IM/IV/PO. Maximum dose: 25mg

Question 8

diphenhydramine hydrochloride (Benadryl)
drug interactions

Answer 8

● Potentiates effects of CNS depressants.
● MAOIs prolong and intensify anticholinergic effects.