Diphenhydramine (Benadryl)

Question 1

Diphenhydramine Classification

Answer 1

Antihistamine

Question 2

Diphenhydramine Mechanism

Answer 2

Nonspecific competitive H1/H2 antagonist -> blocks histamine release, suppresses central cholinergic activity and inhibits reuptake and storage of dopamine, leading to prolonged action of dopamine and reduction of bronchoconstriction, vasodilation, increased vascular permeability.

Question 3

Diphenhydramine Pharmacokinetics

Answer 3

Onset: 10-15m IV, 15-30m IM
Peak Effects: 1-4h
Duration: 6-8h
Half Life: 1-4h

Question 4

Diphenhydramine Indications/Field Use

Answer 4

• Allergic reaction
• Anaphylaxis
• Dystonic reaction

Question 5

Diphenhydramine Contraindications

Answer 5

Hypersensitivity

Question 6

Diphenhydramine Side Effects/Adverse Reactions

Answer 6

Sedation, dries bronchial secretions, blurred vision, HA, palpitations, dizziness, drowsiness, fatigue, euphoria, hypotension

Question 7

Diphenhydramine Dose

Answer 7

Adult: 25-50mg IV IO IM PO
Pedi: 1mg/kg IV IO IM PO, max dose 50mg

Question 8

Diphenhydramine Precautions

Answer 8

Caution with patients with severe liver disease and acute asthma

Question 9

Diphenhydramine Drug Interactions

Answer 9

Potentiates sedative effects of alcohol, benzos, CNS depressants, and MAOI’s.