Antiemetics - H1 receptor blocker

Question 1

Where in the brain is the vomiting centre and chemoreceptor trigger zone located?

1 - hypothalamus
2 - midbrain
3 - pons
4 - medulla oblongata

Answer 1

4 - medulla oblongata

• when stimulated the vomiting centre coordinates the vomiting response

Question 2

The vomiting centre co-ordinates the vomiting response. Which of the following pathways converge and stimulate the vomiting centre to elicit a vomiting response?

1 - vestibular system
2 - vagus nerve
3 - chemoreceptor trigger zone
4 - higher centres (sensory)
5 - all of the above

Answer 2

5 - all of the above

Question 3

Which 2 of the following type of receptors are located on the vomiting centre?

1 - 5-HT3 (serotonin)
2 - D2 dopamine
3 - histamine H1 receptors
4 - muscarinic receptors

Answer 3

3 - histamine H1 receptors
4 - muscarinic receptors

Question 4

The chemoreceptor trigger zone (CTZ) is sensitive to specific stimuli. Which of the following is NOT a receptor located on the CTZ?

1 - 5-HT3 (serotonin)
2 - D2 dopamine
3 - opioid (mu, kappa)
4 - neurokinin-1 (NK1)
5 - GABA

Answer 4

5 - GABA

• these receptors detect emetic agents
• the CTZ then stimulates the vomiting centre

Question 5

Is the chemoreceptor trigger zone (CTZ) located inside or outside the blood brain barrier?

Answer 5

• outside

Question 6

In addition to the vomiting centre and chemoreceptor trigger zone, the 3rd part of the vomiting response is called the vestibular nuclei. Where is this located in the brain?

1 - pons
2 - midbrain
3 - medulla
4 - cerebellum

Answer 6

1 - pons

• receives input from the labyrinth in the inner ear
• this is where motion sickness comes from

Question 7

What type of receptors are located on the vestibular nuclei that are able to receive stimulus from the labyrinth of the inner ear?

1 - 5-HT3 (serotonin)
2 - D2 dopamine
3 - histamine 1 receptors
4 - muscarinic receptors

Answer 7

3 - histamine 1 receptors
4 - muscarinic receptors

Question 8

What is the normal communication pathway between the vomiting centre (VC), chemoreceptor trigger zone (CTZ), and the vestibular nuclei (VN)?

1 - VC to VN to CTZ
2 - CTZ to VN to VC
3 - VN to CTZ to VN or CTZ to VC

Answer 8

3 - VN to CTZ to VN or CTZ to VC

Question 9

Our senses can trigger a vomiting reflex, which is trigger in the higher brain centres. Once stimulated which of the following do they stimulate to initiate vomiting?

1 - vomiting centre (VC)
2 - chemoreceptor trigger zone (CTZ)
3 - vestibular nuclei (VN)?

Answer 9

1 - vomiting centre (VC)

Question 10

Which cells in the stomach are able to detect cytotoxic or other potentially dangerous products?

1 - parietal cells
2 - enterochromaffin like cells
3 - chief cells
4 - mucous cells

Answer 10

2 - enterochromaffin like cells

Question 11

The enterochromaffin like cells of the stomach are able to detect cytotoxic or other potentially dangerous products in the stomach. What neurotransmitter are these cells able to release that ultimately will stimulate the vomiting centre?

1 - 5-HT3 (serotonin)
2 - dopamine
3 - glutamate
4 - GABA

Answer 11

1 - 5-HT3 (serotonin)

• specifically stimulates the vagus nerve

Question 12

During a vomiting response, which of the follow occurs?

1 - lower oesophageal sphincter relaxes
2 - diaphragm and abdominal muscles contract
3 - intra-abdominal pressure increases
4 - autonomic response (tachycardia)
5 - epiglottis closes (reduce aspiration)
6 - all of the above

Answer 12

6 - all of the above

Question 13

Which of the following is the core histamine H1-receptor antagonist that we need to be aware of?

1 - Metoclopramide
2 - Chlorpromazine
3 - Ondansetron
4 - Cyclizine

Answer 13

4 - Cyclizine

Question 14

What is the mechanism of action of cyclizine?

1 - inhibit sensory information from reaching the vestibular nuclei
2 - inhibit H1 receptors on the chemoreceptor trigger zone
3 - inhibit H1 receptors of the vestibular nuclei and the vomiting centre

Answer 14

3 - inhibit H1 receptors of the vestibular nuclei and the vomiting centre

Question 15

Cyclizine is indicated in all of the following except which one?

1 - Motion sickness and vertigo
2 - Narcotic analgesics
3 - Anaesthetics in the post-operative period
4 - Vomiting due GIT infection
5 - Vomiting associated with radiotherapy

Answer 15

4 - Vomiting due to cytotoxic drugs

Question 16

Cyclizine has a number of adverse events. Which of the following is NOT a common adverse event?

1 - drowsiness
2 - dry throat and mouth
3 - constipation
4 - urinary retention
5 - prolonged QT interval

Answer 16

5 - prolonged QT interval

• adverse events are likely to be due to the anti-cholinergic effects (effectively reduced para-sympathetic activity)

Question 17

Cyclizine is contraindicated in patients with hepatic encephalopathy. Why is this?

1 - toxic effects on the liver
2 - build up in the brain and further contribute to cognitive decline
3 - sedative effects could induce liver decompensation

Answer 17

3 - sedative effects could induce liver decompensation, especially increasing the toxicity of alcohol

Question 18

Why should Cyclizine be avoided with alcohol intake?

1 - alcohol inhibits cyclizine
2 - cyclizine induces liver damage
3 - cyclizine increases the toxicity of alcohol

Answer 18

3 - cyclizine increases the toxicity of alcohol

Question 19

Cyclizine should be used in caution with which other drug as it may increase the sedative effects?

1 - beta blockers
2 - amiodarone
3 - verapamil
4 - benzodiazepines

Answer 19

4 - benzodiazepines

• may also accentuate the effects of anticholinergic drugs such as tiotropium

Question 20

What is a standard dose of cyclizine?

1 - 1mg/8 hours as required
2 - 10mg/8 hours as required
3 - 20mg/8 hours as required
4 - 50mg/8 hours as required

Answer 20

4 - 50mg/8 hours as required

• depending on patients symptoms they can be given orally, IV or IM