Anti=emetics

Question 1

How does emesis occur?

Answer 1

Pyloric sphincter closes, cardia and oesophagus relax and gastric contents are propelled by contraction of the abdominal wall diaphragm. The glottis closes and the soft palate elevates to prevent aspiration of vomit.

Question 2

What are causes of emesis?

Answer 2

• Pregnancy
• Medications, toxins
• Pain
• Irradiation
• Smell and touch
• RICP
• Inflammation of the stomach
• Rotational movement

Question 3

What stimulates vomiting?

Answer 3

The vomiting centre is triggered, and you get preliminary signs (nausea, salivation, retching, dilated pupils, sweating, paleness) then you get vomiting.

The vomiting centre is stimulated by acetylcholine, histamine, dopamine and 5-hydroxytryptamine

Question 4

What are anti-emetic drug classes and examples

Answer 4

Dopamine (D2) receptor antagonist - domperidone, metoclopramide

5HT receptor antagonist - ondansetron

Antimuscarinics - hyoscine

Histamine receptor antagonists - Cyclizine

Question 5

What is the MOA, ADR, CI , use of domperidone

Answer 5

Acts on postrema on the floor of the fourth ventricle (vomiting centre). Increases rate of gastric emptying

Oral/PR

Use:
Acute nausea and vomiting (esp induced by L-Dopa or dopamine agonists) – doesn’t cross BBB (oral or PR)

ADR:
Prolactin release (galactorrhoea)
Rarely dystonia

Question 6

What is the MOA, ADR, CI , use of metoclopramide

Answer 6

Acts on postrema on the floor of the fourth ventricle (vomiting centre). Increases rate of gastric emptying
Metoclopramide also has anticholinergic effects and blocks vagal afferent serotonin receptors

Uses:
GI causes of N+V, migraine and post-op (oral, IM, IV)

ADRs:
Extra-pyramidal side effects (avoid in PD), galactorrhoea

Question 7

What is the MOA, ADR, CI , use of ondansetron

Answer 7

Antagonises vagal afferent nerves in GI tract and antagonises receptors on vomiting center

IV, IM, oral

Use:
High doses in radiation sickness, chemo and post-op (given IV, IM or orally), enhanced by single dose of corticosteroid

ADR
Headaches
Constipation
Flushing

Question 8

What is the MOA, ADR, CI , use of hyoscine

Answer 8

Antagonises muscarinic cholinergic receptors

Use:
Motion sickness – orally or a patch – short lived effects

ADR
Systemic anticholinergic side effects
Bradycardia
Tolerance to transdermal hyoscine

Question 9

What is the MOA, ADR, CI , use of cycliizne

Answer 9

Antagonises histamine and muscarinic receptors

Use:
Acute nausea and vomiting (give oral, IV or IM)

ADR
Prolongs QT – contraindicated in myocardial ischaemia
Sedative – crosses BBB