GI: Anti-emetics

Question 1

Name a 5-HT3 receptor antagonist?

Answer 1

Ondansetron

Question 2

When is ondansetron used?

Answer 2

Chemotherapy and radiation emesis

PONV

Question 3

What is the mechanism of action of ondansetron?

Answer 3

Blocks both peripheral and central 5-HT3 receptors
5-HT from drugs results in action potentials which release transmitters to stimulate the NTS and CTz and this the VC
Ondansetron blocks the firing of these potentials

Question 4

What is the results of 5HT 3 antagonists?

Answer 4

reduce ACUTE vomiting

less effective in the delayed phase

Question 5

Which setron is better at preventing delayed emesis?

Answer 5

Palonosetron

Question 6

When are HT antagonists not effective

Answer 6

Motion sickness or dopamergic trnasmission induced vomitng

Question 7

What are the side effects of setrons

Answer 7

Headache

Constipation

Question 8

Name a Neurokinin receptor antagonists

Answer 8

Aprepitant

Question 9

What is the mechanism of NK1 receptors?

Answer 9

Block NK1 receptos in the VC and CTZ that can be stimulated by endogenous substances

Question 10

When are NK1 blockers used

Answer 10

Late phase emesis and PONV

Question 11

Name a muscarinic receptor antagonist used to reduce emesis?

Answer 11

Hyosine

Question 12

When is hysoine used?

Answer 12

Prophylacxis and treatment of motion sickness

Question 13

What is the mechanism of action of hysosine?

Answer 13

Block M acetylecholine receptors at mutlipe sites eg NTS and VC
Directly inhibit GI movements and relax GO tract

Question 14

What are the side effects of hysosine?

Answer 14

Numerous eg blurred vision, urinayr retention, dry mouth, sedation

Question 15

Name a Histamine H1 receptor antagonis used to treat emesis?

Answer 15

Cyclizine

Question 16

When are H1 blockers used?

Answer 16

Motion sichness

Acute labyrinthitis

Question 17

What is cyclizines mechanism of action?

Answer 17

Blockade of H1 receptors in vestibular nuclei and NST

Question 18

What are the side effects of cyclizines?

Answer 18

Sedation and drowsiness

Question 19

Name two dopamine receptor antagonists used in emesis?

Answer 19

Domperidone and metoclopramide

Question 20

When are they used?

Answer 20

Drug induced vomiting - do not use in children

Not effective in motion sickness

Question 21

What is the mechanism of action of dopamine receptor antagonists?

Answer 21

Centrally block dopamine D2 receptors in the CTZ

Peripherally exert a prokinetic action on the oesophagus, stomach and intestine

Question 22

What are the side effects of domperidone and metoclopramide?

Answer 22

Domperidone does not cross the BBB and is less likely to result in the many unwanted effects of metoclopramide [e.g. disorders of movement (extrapyramidal effects)]

Question 23

When is phenothiazine used?

Answer 23

Sever nausea and vomiting

Question 24

Name a cannabinoid?

Answer 24

Nabilone

Question 25

When are cannabinoids used?

Answer 25

Cytotoxic chemotherapy emesis - last resort

Question 26

How do cannabinoids work?

Answer 26

Decreases vomiting induced by agents stimulating the CTZ. Evidence suggests that opiate receptors are involved in drug effect

Question 27

What are side effects of cannabinoids?

Answer 27

Dizziness, dry mouth, mood changes