Benadryl (Diphenhydramine)

Question 1

Class (2)

Answer 1

• Antihistamine

- H1 blocker

Question 2

Actions (3)

Answer 2

• Blocks histamine at H1 receptor sites (competes for these sites) with the following effects if successful: reversal of histamine induced bronchoconstriction/vasodilation/increased capillary permeability–note: H1 receptors causes bronchoconstriction and contraction of the gut
• Reverses drug induced extrapyramidal reactions (EPS) of muscle tremor and rigidity from phenothiazines (Trilafon, Stelazine, Compazine, Phenergan, Thorazine, Mellaril, Prolixin and others) and butyrophenones (Haldol)
• Mild sedative

Question 3

Indications (3)

Answer 3

• Allergic reaction
• In anaphylaxis, Benadryl is given after Epi because Epi causes immediate bronchodilation by its B2 effects and vasoconstriction by its alpha effects
• Acute dystonic reactions (EPS)

Question 4

Dosage/Route

Answer 4

• Adult allergic reaction without shock: 25 mg IV, repeat if needed in 10 minutes; if no IV, 50 mg IM
• Adult allergic reaction with shock: 50 mg IV/IO; if not IV/IO, 50 mg IM

Question 5

Standard Prep

Answer 5

50 mg/ml

Question 6

Pediatric Dose

Answer 6

Pedi allergic reaction without/with shock: 1 mg/kg up to 25 mg IV slowly; if no IV give IM

Question 7

Contraindications (2)

Answer 7

• Hypersensitivity

- Lower respiratory disease such as acute asthma attacks

Question 8

Side Effects (4)

Answer 8

• Sedation
• Dry mouth
• Thickening of bronchial secretions
• Hypotension (rare)

Question 9

Precaution

Answer 9

Potentiates effects of EtOH/CNS depressants