Anti-Emetics

Question 1

Define emesis

Answer 1

Emesis – the act or instance of vomiting

Physical event

Question 2

Stages of vomiting

Answer 2

Occurs in motion sickness, and vestibular disorders…
Accompanies Numerous Disease States
Accompanies Changes in Physiological Status

Question 3

Unwanted Side Effect of Clinically-Used Drugs

Answer 3

Chemotherapy-Induced Nausea & Vomiting (CINV)

Anaesthetics: Post Operative Nausea & vomiting (PONV

Question 4

What is an emetic?

Answer 4

agent which causes vomiting

Question 5

What is an anti-emetic?

Answer 5

agent which prevents vomiting

Question 6

Vomiting reflex

Answer 6

vomiting reflex regulated by the CNS
emesis is controlled and centralized within the brain stem in a neural network on the dorsal surface of the medulla
3 major inputs to the dorsal vagal complex which cause nausea and vomiting:
1. The Chemo receptor Trigger Zone
- central pathway, Brain stem emetic control centre
- on blood side of blood brain barrier
- sensitive to chemicals, main site of action for drugs
2. Vagal pathway
- supplemented with Splanchnic nerves in the GI tract, higher centres e.g smell, vision, pharynx
3. Vestibular pathway

Question 7

Histamine receptor antagonists

Answer 7

work on the vestibular pathway 
> H1 antagonists/antihistamines 
Eg. Cyclizine - motion sickness, Cinnarizine - motion sickness, vertigo, Promethazine - severe morning sickness
- SE = drowsiness, sedation 
> H3 agonists
Eg. Betahistine, Hydrochloride
- activates H receptors on blood vessels in inner ear, causing local vasodilation
- SE = GI disturbances, headache, rashes

Question 8

Muscarinic receptor antagonists

Answer 8

work on vestibular pathway
Eg. Hyoscine, Scopolamine 
- non-selective antagonists
- motion sickness
- oral/transdermal patches applied
- SE = dry mouth, blurred vision, less sedative effects

Question 9

Dopamine receptor antagonists

Answer 9

work on chemoreceptor trigger zone
Eg. Phenothiazines 
- used in severe morning sickness
- oral, i.v
- SE = sedative, hypotension, dystonia 
Eg. Domperidone 
- doesn't penetrate BBB
- used for migraines, cytotoxic 
- therapy-induced emesis, oral, i.v
Eg. Metoclopramide
- penetrates BBB
- increases GI motility
- oral, i.v
- SE = fatigue, menstrual disorders, motor restlessness

Question 10

Serotonin receptor antagonists

Answer 10

work on vagal pathway
Eg. Ondansetron
- drug of choice for cancer-induced nausea and vomiting and post-operative nausea and vomiting
- oral, i.v, i.m
- SE = GI disturbances, headache

Question 11

Nk1 receptor antagonists

Answer 11

work on chemoreceptor trigger zone
active in late stage emesis with cytotoxic drugs
Eg. Aprepitant
- substance P antagonist
- used for CINV and PONV
- i.v, oral
- SE = fatigue, constipation/diarrhoea, decreased appetite

Question 12

Anti-emetic action of Canabis

Answer 12

Eg. Nabilone

• mimetic of main chemical component of canabis
• valuable in treatment of CIN- thought to act via opioid receptors in CTZ
• oral
• SE = drowsiness, mood changes, postural hypotension

Question 13

Corticosteroids

Answer 13

Eg. Dexamethasone

• vomiting caused by cytotoxics (chemo)
• used in combination with D2, 5HT2 antagonists = improves actions

Question 14

Use of drugs to induce emesis

Answer 14

Used when:
- poisonous substances and ingested
- drug overdose
- alcohol intoxication 
patient must be fully conscious
Eg. Syrup of Ipecacuanha 
- 2 alkaloids emetine and cephaline
- oral, works in 15 mins
- irritates GI mucosa
Eg. Apomorphine
- directly stimulates CTZ and VC
- i.m, s.c, acts in 5-10 mins
Eg. Activated Charcoal
- mostly commonly used, binds toxins