Antiemetics

Question 1

Chemoreceptor trigger zone

Answer 1

Out side the brain barrier

Question 2

Receptor in area postrema

Answer 2

• Muscarinic M 1
• Histaminergic H 1
• Serotoninergic 5HT 3 • Dopaminergic D 2
• NK1 receptor for substance P
• Cannabinoids (agonists

Question 3

Prokinetics drug

Answer 3

Metoclopramide
Domperidone Cisapride

Question 4

Prokinetics action

Answer 4

increases the movement of substances
from mouth to caecum( orocaecal transit). So
agonists facilitate GI movement

Question 5

Metoclopramide uese

Answer 5

1.Blocks D 2
and 5HT3 receptors in the GIT.

2.Blocks D 2
receptors in the CTZ.
3. 5HT4 agonism – gastric hurrying
4. Increase in lower esophageal tone. so useful in GERD (gastroesophageal reflex
disease).

Question 6

Metoclopramide ADR

Answer 6

Crosses BBB, placenta and is secret in milk
Sedation, dizziness, muscle dystonias. Long term use leads to parkinsonism and
galactorrhoea
Muscle dystonia, parkinsonism- D2 blockade in NS pathway Galactorrhea - D2 receptors in anterior pituitary are affected

Question 7

Domperidone

Answer 7

Blocks D
2
in the GIT and CTZ.
• Less effects compared to metoclopramide.
• Crosses BBB poorly; so no central effects,no EPS.
• Hence drug of choice in L dopa induced vomiting.
• Orally administered, not parenterally available.
• Drug preferred in GERD

Question 8

Cisapride, prucalopride

Answer 8

No action on D 2
• 5HT 4
agonism
• Cisapride produces gastric hurrying effect. cause prolonged QT syndrome
when combined with CYP 450 inhibitors ( hence
not used now).

• Prucalopride increases GI motility without
affecting gastric emptying. Use for constipation

Question 9

Antipsychotics / neuroleptics

Answer 9

Effective in chemotherapy and radiation induced
emesis. (NOT the drug of choice)
Adverse effects include extrapyramidal symptoms-
due to blockade of Nigrostriatal D 2
. Chlorpromazine,haloperidol.

Question 10

5HT
3
Antagonists

Answer 10

Ondansetron, Granisetron

Question 11

5HT
3
Antagonists

Answer 11

• Cytotoxic drugs and radiation cause release of 5HT
in the GIT and blood – vomiting (5HT3 mediated).
• Drug of choice for CRIE-chemotherapy radiation
induced emesis

Question 12

3.Cannabinoids

Answer 12

Dronabinol
inhibits neurons around the
vomiting centre).

Question 13

2.Substance P antagonists( NK1 receptor)

Answer 13

Aprepitant – delayed emesis in platinum compounds
is prevented. Not for acute vomitin

Question 14

1.Corticosteroids

Answer 14

Dexamethasone i/v