PreOp Meds: H1 Antagonist concepts

Question 1

Histamine-1 receptor activation can mimic these other receptor types.

Answer 1

• Muscarinic
• Cholinergic
• 5HT3
• α-adrenergic

Question 2

Histamine binding to H1 receptors generally elicits what effects?

Answer 2

• Hyperalgesia
• Inflammatory pain (insect stings)
• Allergic rhino-conjunctivitis s/s

Question 3

How prone are H1 antagonists to tachyphylaxis?

Answer 3

• Very little tachyphylaxis development

Question 4

What signs/symptoms occur with excessive H-1 & H-2 activation?

Answer 4

• Hypotension (from NO) release
• ↑capillary permeability
• Flushing
• Prostacyclin release
• Tachycardia

Question 5

What are the side effects of H1 antagonists?

Answer 5

• Drowsiness/sedation
• Blurred vision
• Urinary retention
• Dry mouth

Question 6

What are four examples of H1 receptor antagonists?

Answer 6

• Diphenhydramine (Benadryl)
• Promethazine (Phenergan)
• Cetirizine (Zyrtec)
• Loratidine (Claritin)