Wk 3 Histamine/Antihistamine

Question 1

What is histamine receptor and the main pharmacological action of histamine?

Answer 1

histamine receptor - a class of G-protein-coupled receptors, which bind histamine as their primary endogenous ligand

histamine - stored in mast cells & basophils → mainly existed in lungs, GIT, skin → causes bronchoconstriction

Question 2

Describe the “Triple Response” to histamine and the role of histamine in allergy

Answer 2

• localised reddening of skin
• surrounding flare
• wheal (localised oedema)

Question 3

Discuss the differences between sedating and nonsedating antihistamines, what are their therapeutic uses, and give examples of each group

Answer 3

sedating antihistamines (1st generation)

• promethazine, doxylamine
• they can cross BBB and cause sedation, drowsiness
• MOA: block/inhibit the action of histamine at H1 receptors
• Indication: allergic rhinitis, hives, skin rashes, prophylactic use [often used in cough/cold prophylaxis]
• CON: don’t combine with alcohol, benzos [depressant effect]
• AEs: sedation, dry mouth, constipation, urinary retention

> 1st gen is more sedating than 2nd gen

less-sedating antihistamine (2nd generation)

• fexofenadine, loratadine, cetirizine
• do not cross BBB
• MOA: block/inhibit the action of histamine at H1 receptors
• Indication: allergic rhinitis, hives, skin rashes, prophylactic use
• CON: renal impairment
• AEs: drowsiness, fatigue, headache