Benadryl/ Diphenhydramine

Question 1

Benadryl Class

Answer 1

• Antihistamine

* H1 Antagonist

Question 2

Benadryl Action

Answer 2

• Blocks H1 receptors
H1—causes bronchoconstriction, contraction of gut
H2—causes peripheral vasodilation, secretion of gastric acid
• H1 antagonists have anticholinergic properties in varying degrees.
Probably accounts for antidyskinetic effects. Also may
be responsible for anti-emetic effects.

Question 3

Benadryl Indications

Answer 3

• Anaphylaxis
• Allergic reactions
• Urticaria
• Sedation
• Motion Sickness / Vertigo
• Nausea and Vomiting
• Histamine release secondary to DXM Use.
• Extrapyramidal (Dystonic) reaction

Question 4

Benadryl Contraindications

Answer 4

• Hypersensitivity
• Acute asthma attack
• Lower respiratory tract disease
• Newborns and nursing mothers

Question 5

Benadryl Precautions

Answer 5

• HTN
• Cardiac disease
• Renal disease
• Bronchial asthma
• Seizures
• Pregnancy category - C
• Closed angle glaucoma (avoid if at all possible)

Question 6

Benadryl Dosage

Answer 6

• Adults: 25-50 mg IV or IM

* Pediatrics: 1-2 mg/kg IV/IM/IO max dose 25 mg PO: (If available) 25 mg (for mild cases)

Question 7

Benadryl Onset/ Duration

Answer 7

• Onset : IV immediate, IM 30 min

* Duration: 4-7 hrs

Question 8

Benadryl Side Effects

Answer 8

• Drowsiness
• Dizziness
• Incoordination
• Confusion
• Dry mouth
• Drying of bronchial secretions
• Blurred vision
• Urinary retention
• Hypotension
• Tachycardia
• Bradycardia

Question 9

Benadryl Interactions

Answer 9

• Additive effects—other CNS depressants

* MAOIs—prolong the anticholinergic effects