CPTP 3.14 Antihistamines

Question 1

Diphenhydramine

Pharmacodynamics + side effects

Answer 1

1st gen antihistamine

Side effects

• sedation
• not very selective for H1, some muscarinic binding
• antimuscarinic effects (pupil dilation, dry mouth, constipation, bronchodilation, hypertension, tachycardia)

Question 2

Chlophenamine

Pharmacodynamics + side effects

Answer 2

1st gen antihistamine

Side effects

• sedation
• not very selective for H1, some muscarinic binding
• antimuscarinic effects (pupil dilation, dry mouth, constipation, bronchodilation, hypertension, tachycardia)

Question 3

Cetirizine

Pharmacodynamics + side effects

Answer 3

2nd gen antihistamine

Side effects
-less sedation (don’t cross BBB)

Question 4

Fexofenadine

Pharmacodynamics + side effects

Answer 4

3rd gen antihistamine

Side effects

• less cardiotoxic
• less muscarinic activity

Question 5

Where is histamine produced

Answer 5

• Mast cells, basophils
• ECF cells in gastric mucosa
• Histaminergic neurons in brain

Question 6

Effect of H1 receptor

Answer 6

• Smooth muscle contraction (bronchoconstriction)
• Vasodilation (erythema)
• Immune response (contraction & separation of endothelial cells in odema, wheal response)
• Increases HR & constriction
• Sensitisation of peripheral afferent nerve terminals for pain, itch

Question 7

Effect of H2 receptor

Answer 7

• Increases HR & constriction

- Increases gastric acid secretion

Question 8

Effect of H3 receptor

Answer 8

-Causes epilepsy, wakefulness

Question 9

What do do when someone is anaphylactic shock

Answer 9

1. Remove Ag exposure
2. Antihistamine
3. IM adrenaline
4. Glucocorticoid

Question 10

Effect of adrenaline on receptors:
alpha1
beta1
beta2

Answer 10

alpha1: vasoconstriction
beta1: increases HR + force (relieves hypotension)
beta2: bronchodilation