Diphenhydramine (Benadryl)

Question 1

Class

Answer 1

Antiemetic
H1 Blocker
Antihistamine

Question 2

Actions

Answer 2

Mild sedative
Blocks H1 at H1 receptor sites (by competing for these sites) with the following effects if successful: reversal of histamine induced bronchoconstriction, capillary permeability, and vasodilation.
Note H1 receptors cause bronchoconstriction and contraction of the gut.
Reverses extrapyramidal reactions (EPS) or muscle tremor and rigidity from phenothyazines (trilafon, stelazine, compazine, phenergan, thorazine, mellaril, prolixin, etc) and butyrophenones (haldol).

Question 3

Indications

Answer 3

Acute dystonic reactions
Anaphylaxis / allergic reactions
In anaphylaxis, epinephrine is given before benadryl because epinephrine has immediate beta 2 bronchodilation effects and alpha vasoconstriction adrenergic effects

Question 4

Contraindications

Answer 4

Hypersensitivity
Use within 14 days of an MAOI.
Lower respiratory diseases such as acute asthma attacks.

Question 5

Side effects

Answer 5

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

Question 6

Precautions

Answer 6

Potentiates the effects of ETOH/CNS depressants.

Children/infants/neonates are at risk of a paradoxical reactions.