Anti-histamines (Drugs)

Question 1

What are the anti-histamines?

Answer 1

1. H₁ receptor antagonists
2. H₂ receptor antagonists

Question 2

What are the inhibitors of mast cell degranulation?

Answer 2

1. Sodium cromoglycate
2. Omalizumab
3. β₂-adrenoreceptor agonist
4. PDE inhibitors

Question 3

What is the mechanism of action of sodium cromoglycate?

Answer 3

Stabilises mast cells and prevents degranulation by reducing [Ca2+] influx, possibly by reducing inward Cl^- conductance.

Question 4

What is the mechanism of action of omalizumab?

Answer 4

Sequesters IgE and prevents binding to FcεR1 receptors.

Question 5

What is the mechanism of action of β₂-adrenoreceptor agonists and PDE inhibitors in inhibition of mast cell degranulation?

Answer 5

Raised intracellular [cAMP] inhibits mast cell degranulation

Question 6

What are examples of 1st generation H₁ receptor antagonists?

Answer 6

1. Mepyramine
2. Promethazine

Question 7

What are the clinical uses of 1st generation H₁ antagonists?

Answer 7

• Sedative
• Motion sickness
• Morning sicknes

Question 8

What are examples of 2nd genration H₁ antagonists?

Answer 8

Terfenadine

Question 9

What are examples of 3rd generation H₁ receptor antagonists?

Answer 9

1. Fexofenadine
2. Loratadine

Question 10

What are the clinical uses of 3rd generation H₁ antagonists?

Answer 10

• Hay fever
• Urticaria

Question 11

What drugs can be used to raise [cAMP]_i and inhibit mast cell degranulation?

Answer 11

• β₂-adrenoreceptor agonists (e.g. salbutamol)
• PDE inhibitors (e.g. theophylline)

Question 12

What is the difference between 1st and 2nd generation antihistamines?

Answer 12

1st generation crossed BBB and caused CNS effects (e.g. drowsiness due to arousal effects of histamine) while 2nd generation didn’t

Question 13

What was the major side effect of terfenadine?

Answer 13

• Caused long QT syndrome and sudden cardiac death
• Due to inhibition of hERG channels in cardiac tissue (responsible for repolarisation)

Question 14

What is the pharmacokinetics of terfenadine?

Answer 14

Prodrug metabolised to active fexofenadine by cyt3A4 in liver.

Question 15

What drugs are used to treat allergic reactions and mastocytosis?

Answer 15

1. Inhibitors of mast cell degranulation
2. Anti-histamines
3. RTK inhibitor (mastocytosis only)

Question 16

What is imatinib used for and its mechanism of action?

Answer 16

• Use: Treatment of mastocytosis
• Mechanism of action: RTK inhibitor

Question 17

What is a CCK inhibitor?

Answer 17

Proglumide

Question 18

What are the H₂ receptor antagonists?

Answer 18

• Cimetidine
• Ranitidine

Question 19

What is a proton pump inhibitor?

Answer 19

Omeprazole

Question 20

How is anaphylactic shock treated?

Answer 20

IV injection of adrenaline

Question 21

What drugs are used to treat gastric ulcers?

Answer 21

Inhibitors of gastric acid secretion:

1. CCK inhibitors
2. H₂ antagonists
3. Proton pump inhibitors
4. Antacids
5. ACh inhibitors
   (6. Vagotomy, not drug)

Treatment of H. pylori infection: Clarithromycin

Question 22

What is the preferred drugs used for first-line treatment of gastric ulcers clinically?

Answer 22

Proton pump inhibitors

Question 23

What is the mechanism of action of misoprostol?

Answer 23

• PGE₂ analogue
• Co-administered with NSAIDs to prevent gastric side-effects

Question 24

What is arthrotec?

Answer 24

Diclofenac (NSAID) + Misoprostol