Pharmacology: allergic rhinitis

Question 1

What type of chemical is histamine?
Where is histamine found?
What are 3 functions of histamine?

Answer 1

Neurotransmitter
Skin, lungs, brain
Sleep/wake regulation, food and water intake, temperature regulation

Question 2

What receptors does histamine act on?

Answer 2

H1-H4 receptors

Question 3

What is the role of H1 receptors?

Answer 3

involved in vasodilation, increased vascular permeability, contracting SMCs (except in BV’s)

Question 4

What is the role of H2 receptors?

Answer 4

Stimulates gastric secretion (link to GI system)

Question 5

TYPE 1 IMMEDIATE HYPERSENSITIVITY REACTIONS
What causes a type 1 immediate hypersensitivity reaction?
Is it a localised or generalised reaction?
Does it happen immediately or after delay?

Answer 5

Occurs immediateyl after antigen-antibody interaction in a sensitised tissue
Localised, immediate

Question 6

TYPE 1 IMMEDIATE HYPERSENSITIVITY REACTIONS
What is the role of histamine in type 1 immediate hypersensitivity reactions?

Answer 6

Histamine is exocytosed from mast cells.
Acts predominantly on H1 receptors to cause
- Vasodilation –> reddening of the skin
- Wheals: increased permeability of post capillary venuls
- Flare: sensory nerve reflex causing the release of vasodilation and itching

Question 7

TYPE 1 IMMEDIATE HYPERSENSITIVITY REACTIONS
Does the outcome of a type 1 hypersensitivity reaction depend on the location? Give 2 examples

Answer 7

Yes
Skin - urticaria (itching)
Allergic rhinitis: eyes, nose, throat.

Question 8

ANTIHISTAMINES
1st generation antihistamines
- Describe selectivity
- Does it cross the BBB? Implications of this?
- 2 examples?

Answer 8

Non selective histamine receptor antagonists; also binds to muscarinic receptors
Yes –> leads to drowsiness
Doxylamine, promethazine

Question 9

2nd generation antihistamines
- Describe selectivity
- Does it cross the BBB? Implications of this?
- 2 examples?

Answer 9

More selective to H1 receptors
Less so –> less drowsiness
Loratadine, fexofenadine

Question 10

Can some antihistimates be given by the optical/intranasal route?
Implications for this?
Example?

Answer 10

Yes
The site of allergic rhinitis?
Levocabastine

Question 11

What are 3 addtiional indications for antihistamines?

Answer 11

Induce sleep
Reduce nausea and vomiting
Reduce motion sickness

Question 12

What are 4 adverse effects of antihistamines?

Answer 12

Sedation (less for 2nd generation)
Dry mouth, reduced respiratory secretions
GI disturbance - inhibits gastric secretions via H2
Urinary retention