GIT: Anti-emetic drugs, diarrhoeals, Laxatives, Acid secretion

Question 1

Describe the basic mechanism of action of anti-emetic drugs.

Answer 1

Antiemetics work on the neural pathways involved with vomiting by blocking specific receptors that respond to neurotransmitter molecules, such as serotonin, dopamine, and histamine. Most of these are central receptors found in the vomiting center of the brainstem, while peripheral receptors are found in the vagus nerve. When the gastrointestinal tract senses a threat, it sends information to the peripheral receptors, which in turn convey the information to the central receptors in the vomiting center. In response, the vomiting center triggers nausea and vomiting by stimulating the gastrointestinal tract, abdominal muscles, and the diaphragm.

Question 2

List 5 classes of anti-emetic drugs and their indications.

Answer 2

• The main antiemetic classes include antagonists of the serotonin, dopamine, histamine, muscarinic and neurokinin systems, corticosteroids and benzodiazepines. Some antiemetics appear more effective for specific indications.
• Serotonin and neurokinin antagonists, such as ondansetron and aprepitant, are highly effective in treating chemotherapy-induced nausea and vomiting. Metoclopramide and antihistamines are first-line options for nausea and vomiting in pregnancy.
• Serotonin antagonists and some dopamine antagonists, such as metoclopramide, can prolong the QT interval on the ECG. Dopamine antagonists can cause extrapyramidal adverse effects, particularly in children.

Question 3

Describe the basic physiology of nausea and vomiting?

Answer 3

Question 4

What are some side effects of anti-emetics?

Answer 4

1. QT prolongation
2. Extrapyramidal symptoms - dystonia, akathisia and parkinsonism.
3. Sedation
4. Anticholinergic effects
5. Constipation

Question 5

Anti-Emetic Drugs: Dopamine antagonists
- 5 Examples?
- MOA?
- PBS Restrictions?

Answer 5

Question 6

Anti-Emetic Drugs: Serotonin antagonists
- 4 Examples?
- MOA?
- PBS Restrictions?

Answer 6

Question 7

Anti-Emetic Drugs: Neurokinin antagonists
- 4 Examples?
- MOA?
- PBS Restrictions?

Answer 7

Question 8

Anti-Emetic Drugs: Antihistamines
- 4 Examples?
- MOA?
- PBS Restrictions?

Answer 8

Question 9

Give an example plus the MOA for the following anti-emetic drugs:
- Anticholinergics?
- Corticosteroids?
- Benzodiazepines?

Answer 9

Question 10

Anti-Emetic Drugs: Cannabinoids
- 4 Examples?
- MOA?
- PBS Restrictions?

Answer 10

Question 11

Which 2 antiemetics are indicated for Gastroenteritis?

Answer 11

1. Dopamine antagonists (S4)
2. Serotonin antagonists (S4)

Question 12

Which 2 antiemetics are indicated for Opioid-induced nausea and vomiting?

Answer 12

1. Serotonin antagonists (S4)
2. Dopamine antagonists (S4) - droperidol

Question 13

Which antiemetics are indicated for:
- Migraine-related nausea and vomiting?

Answer 13

Dopamine antagonists (S4)
- metoclopramide with paracetamol (S3)
- metoclopramide (S4)
- prochlorperazine (S3 or S4)

Question 14

Which antiemetics are indicated for:
- Chemotherapy-induced nausea and vomiting?

Answer 14

1. Serotonin antagonists (S4)
2. Neurokinin-1 antagonists (S4)
3. Corticosteroids (S4) - dexamethasone
4. Dopamine antagonists (S4) - olanzapine, haloperidol
5. Benzodiazepines (S4) - lorazepam

Question 15

Which antiemetics are indicated for:
- Radiation-induced nausea and vomiting?

Answer 15

1. Serotonin antagonists (S4)
2. Corticosteroids (S4) - dexamethasone
3. Dopamine antagonists (S4)

Question 16

Which antiemetics are indicated for:
- Pregnancy?

Answer 16

Question 17

Which antiemetics are indicated for:
- Vestibular causes of nausea and vomiting?

Answer 17

1. Antihistamines (S3) -diphenhydramine (Benadryl), meclizine (Bonine), promethazine (Phenergan), dimenhydrinate (Dramamine, Gravol)
2. Anticholinergics (S3)
3. Dopamine antagonists (S4)

Question 18

Which antiemetics are indicated for:
- Postoperative nausea and vomiting?

Answer 18

1. Dopamine antagonists (S4)
2. Serotonin antagonists (S4)
3. Antihistamines (S3)
4. Corticosteroids (S4) - dexamethasone
5. Neurokinin-1 antagonists (S4)
6. Benzodiazepines (S4) - lorazepam

Question 19

Describe how some anti-emetics can cause QT prolongation?

Answer 19

Question 20

Describe how some anti-emetics can cause Extrapyrimidal symptoms?

Answer 20

Question 21

Describe how some anti-emetics can cause Sedation?

Answer 21

Question 22

Describe how some anti-emetics can cause Anticholinergic effects?

Answer 22

Question 23

Describe how some anti-emetics can cause Anticholinergic effects?

Answer 23

Constipation - Constipation is a well-described adverse reaction to serotonin antagonists such as ondansetron and anticholinergic drugs such as hyoscine.4 Dopamine antagonists such as metoclopramide and domperidone are prokinetic so may be a better choice for patients with constipation.