Anti-Emetics

Question 1

Name the types of anti-emetics and where they act

Answer 1

D2 receptor antagonists - visceral afferents from the gut and CTZ

5HT3 receptor antagonists - visceral afferents from the gut and CTZ

Muscarinic receptor antagonists - vestibular nuclei and CTZ

H1 receptor antagonists - vestibular nuclei and CTZ

Corticosteroids - CTZ

Cannabinoids - CTZ

NK1 receptor antagonists - CTZ

Question 2

What is the CTZ, where is it found and what stimulates it

Answer 2

CTZ - chemoreceptor trigger zone. Found within the medulla oblongata and stimulates vomiting. Inputs include:

Sensory afferents via midbrain

Direct triggers

Vestibular nuclei

Visceral afferents from gut

Question 3

Name a muscarinic receptor antagonist

Answer 3

Hyoscine hydrobromide

Question 4

How do muscarinic receptor antagonists work and what are they useful for

Answer 4

Muscarinic receptor antagonists competively block muscarinic ACh receptors in the vestibular nuclei and in the CTZ but will affect all mAChR in the body

Good for those who cannot take tablets, for motion sickness and bowel obstruction

Question 5

Name some side effects of muscarinic receptor antagonists

Answer 5

Sedation

Memory problems

Glaucoma

Dry mouth

Constipation

Question 6

Name some H1 receptor antagonists

Answer 6

Cyclizine - main one used

Levomepromazine

Cinnarizine

Promethazine - pregnancy

Diphenhydramine

Question 7

How do H1 receptor antagonists work and name some uses

Answer 7

H1 receptor antagonists work by acting on the vestibular nuclei to inhibt H1 receptors. Also inhibit histaminergic signals from vestibular system to the CTZ

Uses include motion sickness and morning sickness

Question 8

Name some side effects of H1 receptor antagonists

Answer 8

Sedation - more prominant in children and old ladies given cyclizine

Excitation

Antimuscarinic - dry mouth, constipation, retention

Cardiac toxicity (long QT)

Question 9

Name some serotonin receptor antagonists

Answer 9

Ondansetron

Granesitron

Palonosetron

Question 10

Describe how serotonin receptor antagonists work as an anti-emetic and when are they used

Answer 10

5HT receptor antagonists act peripherally to decrease GI motility and secretions. Also act centrally to inhibit the CTZ

Used as first line treatment in emesis

Question 11

Name some side effects of serotonin receptor antagonists

Answer 11

Constipation
Headache

Elevated liver enzymes

Long QT

Extra-pyramidal effects - dystonia, parkinsonism

Question 12

Name the D2 receptor antagonists

Answer 12

Metoclopramide

Domperidone

Chlorpromazine

Haloperidol

Question 13

Describe how metoclopramide works and what it is used for

Answer 13

Metoclopramide increases ACh at muscarinic receptors in the gut to increase gastric emptying and increase peristalsis

It promotes gastric emptying by increasing tone at LOS, increasing tone and amplitude to gastric contractions and decreasing tone of pyloric sphincter

Good for GORD and ileus

Question 14

What are the side effects of metoclopramide

Answer 14

Galactorrhoea

Extra-pyramidal effects - dystonia and parkinsonism

Question 15

What are the uses and side effects of the D2 receptor antagonists, excluding metoclopramide and domperidone

Answer 15

Uses: motion sickness, vertigo, pregnancy

Haloperidol good for chemotherapy and palliation

Side effects include: extra-pyramidal effects (dystonia, parkinsonism), sedation, hypotension

Question 16

Name some corticosteroids used as antiemetics

Answer 16

Dexamethasone

Methylprednisolone

Question 17

Describe how corticosteroids act as antiemetics and when they are used

Answer 17

Corticosteriods act on the CTZ but may have properties of D2 receptor antagonists. Also have anti-inflammatory effects

Good for perioperative nausea and vomiting, chemotherapy, palliation (dexamethasone)

Question 18

What are the side effects of corticosteriods

Answer 18

Insomnia

Increased appetite

Increased blood sugar

Question 19

Name some neurokinin 1 receptor antagonists

Answer 19

Aprepitant

Fosaprepitant

Netupitant

Question 20

Describe how neurokinin 1 receptor antagonists work and when they are used

Answer 20

Neurokinin 1 receptor antagonists prevent the action of substance P at CTZ and in peripheral nerves -> blocks vomiting and pain

Also boost effects of 5HT receptor antagonists

Good for chemotherapy in combination with other drugs

Question 21

Name some side effects of neurokinin 1 receptor antagonists

Answer 21

Headache

Diarrhoea

Constipation

Stevens-Johnson syndrome

Question 22

Which antiemetics are used in the treatment of motion sickness

Answer 22

Hyoscine hydrobromide as 1st line

Cinnarizine - fewer side ffects

Question 23

What drugs are used in the treatment of emesis caused by gut problems

Answer 23

Prokinetics for GORD and ileus - domperidone and metoclopramide

Ondansetron and/or cyclizine and then add dexamethasone

Question 24

Which drugs are given in the treatment of hyperemesis gravidarum

Answer 24

Promethazine or prochlorperazine

Then metoclopramide

Then ondansetron

Question 25

Which drugs are given in the treatment of chemotherapy induced emesis

Answer 25

Low risk - dexamethasone

Moderate risk - dexamethasone and ondansetron

High risk - dexamethasone, ondansetron and aprepitant

Metoclopramide for rescue