10.2.1 Anti-emetics, Anti-muscarinics and Anti-histamines

Question 1

In the brain what is responsible for vomiting?

Answer 1

Vomiting centre

Question 2

Where is the vomiting centre found?

Answer 2

Medulla

Question 3

What are the steps of vomiting?

Answer 3

1. Deep breath
2. Glottis closes
3. Abdominal muscle contraction
4. Lower oesophgaeal sphincter relaxes
5. Retrograde peristalsis of small bowels

Question 4

What are parts of the brain, found in the medulla, have involvement with vomiting?

Answer 4

Vomiting centre
- Intergrates incoming signals
- Co-ordinates emesis

Chemoreceptor trigger zone
- Main site for sensing emetic stimuli

Vestibular nuclei (CNVIII)
- Input from the labyrinth
- Balance control

Question 5

What inputs act on the vomiting centre which are not in the medulla?

Answer 5

Higher cortical centres
- Pain
- Repulsive sights and smells
- Emotional factors

Vagal afferents
- Convey signals from gut to brainstem

Enterochromaffin cells
- Sense toxic chemicals or toxins in gut

Question 6

What neurotransmitters act on the vomiting centre?

Answer 6

Neurokinin 1 (NK1)

ACh muscarinic

Histamine 1 (H1)

Serotonin (5HT2)

Question 7

What components of the vestibular nuclei send impulses to the vomiting centre?

Answer 7

Semi-circular canals
Utricle
Saccule

Anything involved in motion

Question 8

What is responsible for motion sickness and what causes it?

Answer 8

Vestibular nuclei

Caused by:
- Travel
- Sudden fast movements (roller coasters)

Question 9

What receptors are present in vestibular nuclei?

Answer 9

ACh Muscarinic
H1

Motor Vehicle - Muscarinic Vestibular

Motor-movement- vestibular = movement

Hearing- vestibulocochlear, other function of CNVIII
Hearing- Histamine

Question 10

What is an example of an anti-muscarinic?

Answer 10

Hyoscine hydrobromide

Works centrally, therefore systemic effects

Question 11

What are the adverse effects of anti-muscarinics

Answer 11

Competitively blocks ACh receptors therefore anti-SLUDGE

Sedation
Constipation
Dizziness
Dry mouth
Visual issues
Confusion

Question 12

When should you not give anti-muscarinics?

Answer 12

Elderly patients
Glaucoma

Question 13

What are some important drug to drug interactions with anti-muscarinics?

Answer 13

Anti-psychotic medications

Question 14

Why is Hyoscine butylbromide not used for motion sickness?

Answer 14

Does not act centrally

Question 15

Where do H1 antagonists act?

Answer 15

Vomiting centre
Vestibular nuclei

Question 16

How do H1 antagonists work?

Answer 16

Inhibits histaminergic signals from vestibular system to CTZ

Question 17

Fill out the table

Answer 17

Question 18

What are the adverse effects of H1 antagonists?

Answer 18

Sedation
Anti-SLUDGE:
- Dry mouth
- Constipation
- Urinary retention
- Blurred vision

Question 19

When should you not give H1 antagonists?

Answer 19

Epilepsy
Glaucoma
Urinary retention
Children
Elderly patients

Question 20

What anti-histamines are sedative?

Answer 20

Cyclizine pill capsules cause drowsiness

Cyclizine
Promethazine
Chlorphenamine
Cinnarizine
Diphenhydramine (Benadryl)

Question 21

What anti-histamines are not sedative?

Answer 21

Cetirizine
Fexofenadine
Loratadine

Question 22

Why are some anti-histamines not sedative?

Answer 22

Second generation anti-histamines are unable to cross the blood brain barrier

Question 23

Who is affected by motion sickness?

Answer 23

Women > men
Children > adults
People who have migraines

Question 24

How can motion sickness be prevented?

Answer 24

Hydration
Position in vehicle
Distraction

Question 25

What drugs are given for motion sickness?

Answer 25

Anti-muscarinics
- Hyoscine hydrobromide

Anti-histamines
- Cinnarizine
- Cyclizine
- Prochlorperazine