1. Treatment of Vomiting & Gut Motility Disorders

Question 1

How is vomiting controlled

Answer 1

By 2 separate units, both in the medulla:
The vomiting centre
The chemoreceptor trigger zone

Question 2

Describe the vomiting centre

Answer 2

Collection of multiple sensory, motor and control nuclei
Mainly in medullary and pontile reticular formation, also extending into spinal cord
Recieve vagal and symp.
Motor impulses are transmitted from vomiting centre

Question 3

Describe the chemoreceptor trigger zone

Answer 3

In the area postrema in the floor of the 4th ventricle
Sensitive to chemical stimuli and is site of anti emesis drugs
Also concerned with mediation of motion sickness

Question 4

Describe how motion sickness causes vomiting

Answer 4

Vestibular labyrinth -> vestibular nuclei -> cerebellum -> CTZ -> vomiting centre -> vomit

Question 5

Name the types of anti-emetic drugs

Answer 5

Antihistamines
Antimuscarinics
Dopamine antagonosts
5HT3 antagonists
Neurokinin 1 receptor antagonists
Synthetic cannabinoids
Steroids

Question 6

Describe antihistamines
MOA?
USE?
SIDE EFFECTS?
EXAMPLES?

Answer 6

H1 histamine receptor antagonists

Useful in N/V, motion sickness, vestibular disorders

Drowsiness and antimuscarinic effects

Cinnarizine
Cyclizine
Promethazine

Question 7

Describe antimuscarinics
MOA?
USE?
SIDE EFFECTS?
EXAMPLES?

Answer 7

Muscarinic receptor antagonists: Blockade of muscarinic receptor-mediated impulses from the labyrinth and from visceral afferents

Useful in motion sickness

Constipation, transient bradycardia, dry mouth

Hyoscine hydrobromide

Question 8

Describe dopamine antagonists
MOA?
USE?
EXAMPLES?

Answer 8

Act centrally as dopamone antagonists on the CTZ

Active against CTZ-triggered vomiting but not stomach induced

Phenothaizines:
Chlorpromazine
Prephenazine
Prochlorperazine
Trifluoperazine

Domperidone

Metoclopramide

Question 9

Describe 5HT3 antagonists
MOA?
USE?
EXAMPLES?

Answer 9

Block 5HT3 receptors in GI tracts and in CNS

Useful in managing N/V in post operative and patients recieving cytotoxics

Dolasetron
Granisetron
Ondansetron
Palonosetron

Question 10

Describe neurokinin 1 receptor antagonists
MOA?
USE?
EXAMPLES?

Answer 10

Adjunct to dexa methasone and a 5HT3 antagonist in preventing N/V associated with chemotherapy

Aprepitant
Fosaprepitant

Question 11

Describe synthetic cannabinoids
USE?
SIDE EFFECTS?
EXAMPLES?

Answer 11

For N/V causes by chemo unresponsiveness to conventional anti-emetocs

Drowsiness, dizziness

Nabilone

Question 12

Describe steroids
USE?
EXAMPLES?

Answer 12

Can be used alone to treat vomiting associated with cancer chemotherapy or in conjunction with other antiemetics

Dexamethasone

Question 13

Name 2 other anti-emetics

Answer 13

Haloperidole

Levomepromazine

Question 14

Name the types of laxatives with an example

Answer 14

Bulk-forming laxatives: ispaghula husk, methylcellulose

Stimulant laxatives: bisacodyl, dantron, docusate sodium, glycerol, senna, sodium picosulfate

Faecal softeners: arachis oil, liquid paraffin

Osmotic laxatives: lactulose, macrogols, magnesium salts, rectal phosphates

Peripheral opioid-receptor antagonists: methylnaltrexone bromide

Question 15

What are the approaches for treatment of acute diarrhoea

Answer 15

Maintance of fluid and electrolyte balance
Antimotility drugs
Antispasmodics (hyoscine butylbromide)
Occasionally antibacterial agent is indicated

Question 16

How is chronic diahhroas treated

Answer 16

Antimotility agents: coedine
Adsorbents
Bulk forming drugs

Question 17

How does colestyramine act as a bile acid sequestrants

Answer 17

Colestyramine is an anion exchange resin
Forms an insoluble compex with bile acids in the intestine
Relieves pruritus associated with partial billary obstruction and primary billary cirrhosis