Antiemetics

Question 1

Dopamine antagonists

Answer 1

Prochlorperazine, metoclopromide, domperidone

Question 2

Cannabinoids

Answer 2

Nabilone

Question 3

Substance P antagonist

Answer 3

Aprepritant

Question 4

Antimuscarinics

Answer 4

Hyoscine

Question 5

Antihistamines

Answer 5

Cinnarazine, promethazine, cyclizine

Question 6

5HT3 antagonists

Answer 6

Odansetron, Granisetron

Question 7

Dopamine antagonists and 5HT3 antagonists are ineffective in reducing the nausea and vomiting of motion sickness

Answer 7

Antimuscarinic drugs or antihistamines, which act directly on the vomiting centre, may be effective, although side-effects are common. Vertigo and vomiting associated with vestibular disease are treated with antihistamines (e.g. promethazine, cinnarizine), phenothiazines or betahistine.

Question 8

The vomiting centre is in the lateral reticular formation of the medulla at the level of the olivary nuclei

Answer 8

It receives afferents from the following: limbic cortex, CTZ, Nucleus solitaruis, spinal cord (spinoreticular fibers), vestibular system

Question 9

Substance P given intravenously causes vomiting

Answer 9

herefore, it was reasoned, antagonists of substance P might have an antiemetic action. This idea led to the introduction of aprepitant, a neurokinin-1 receptor antagonist.

Question 10

Cytotoxic drugs vary in their emetic potential, but some, e.g. cisplatin, cause severe vomiting in most patients.

Answer 10

The emetic action of these drugs seems to involve the CTZ, and the dopamine antagonists are often effective antiemetics.

Question 11

Prochlorperazine

Answer 11

Phenothiozine that has widely been used as an antiemetic

Question 12

Domperidone

Answer 12

similar to metoclopramide, but does not cross the blood–brain barrier and rarely causes sedation or extrapyramidal effects.

Question 13

The 5HT3 antagonists, e.g. ondansetron, lack the adverse effects of dopamine antagonists, but may cause

Answer 13

constipation or headaches

Question 14

It has been shown in clinical trials that the severe vomiting caused by highly emetic cytotoxic drugs is controlled better by combinations of intravenous antiemetic drugs

Answer 14

e.g metoclopramide and dexamethasone

Question 15

Aprepritant

Answer 15

is a neurokinin-1 receptor antagonist that blocks the action of substance P in the CTZ. It is used as an adjunct to dexamethasone and a 5HT3 antagonist to prevent vomiting caused by cytotoxic chemotherapy

Question 16

Nabilone

Answer 16

a synthetic cannabinoid, decreases vomiting caused by agents that stimulate the CTZ. The mechanism of action is unknown but may involve opioid receptors because its antiemetic action is blocked by naloxone. It is used in cytotoxic chemotherapy when other antiemetics have been ineffective. Unwanted effects include drowsiness, dry mouth, hypotension and psychotic reactions.

Question 17

Little is known about the neural mechanisms involved in motion sickness

Answer 17

but it does not occur following labyrinthectomy or ablation of the vestibular cerebellum.

Question 18

Hyoscine is one of the most effective agents for reducing the incidence of motion sickness

Answer 18

muscarinic receptor antagonist and frequently causes drowsiness, dry mouth and blurred vision

Question 19

Cinnarizine is an antihistamine

Answer 19

It has an efficacy similar to that of hyoscine, but produces fewer side-effects. It must be taken 2 h before exposure to provocative stimulation.