Antiemetics

Question 1

What anti-metics are used for cancer patients?

Answer 1

Histamine H1-Receptor Antagnists - Cyclizine, Cinnarizine, Promethazine

Histamine H3-Recepor Antagonists - Betahistin, Hydrochlordie

5-HT3 Receptor Antagonists - Ondansetron, Granisettron, Palonosetron

Muscarinic mACh Receptor Antagonists - Hyoscine, Scopolamine

D2-Receptors Antagonists - Phenothiazines, Prochloropromazine, Perphenazine

Cannabinoids - Nabilone

Dexamthasone

Corticosteroids

Neurokinin-1 Antagonists - Aprepitant

Question 2

What is the physiology of emesis?

Answer 2

• Controlled by the CNS (medulla)
• There are 3 major inputs to the dorsal vagal complex:
• 1) chemoreceptor trigger zone 2) the vagal pathway (GIT pharyx, senses) 3) vestibular pathway (in ear).
• Need to block the neurotransmitters (and the receptor they come from) involved in the triggering or emesis response:
• Serotonin -5HT3 Receptors
• ACh - Muscarinic Receptors
• Dopamine - D2 Receptor
• Substance p - NK1 Receptor
• Histamine - H1 Receptor
• Enkephalin - Delta Receptor

Question 3

Examples of Histamine H1 Receptor Antagonists

Answer 3

Cyclizine (motion sickness)

Cinnarzine (motion sickness/vestibular disorders)

Promethazine (pregnancy morning sickness)

Question 4

Side effects of H1 receptors

Answer 4

Drowsiness, sedation

Question 5

H3 agonist > Anti vertigo drugs

Answer 5

Betahistine

Hydrochloride

Question 6

What is the role of h3 Agonist

Answer 6

Acts on blood vessel in the inner ear

Side effects are: GI probs, headache, rash, itcing

Question 7

Examples of Muscarinic Receptor Antagonists

Answer 7

• Hyosine
• Scopolaimine

Question 8

Side effects of Muscarinic receptor antagonist

Answer 8

• dry mouth
• blurred vision
• less sedative

Question 9

What are Dopamine receptor antagonists

Answer 9

Have a powerful anti-emetic action. Antagoise muscarinic/histamine receptors

to treat severe morning sickness

Question 10

Example of a dopamine receptor antagonist to treat morning sickness

Answer 10

• Phenothiazines

Side effects: sedative, hypotension, dystonia, dyskinsia

Question 11

Example of dopamine receptor antagonist which Penetrates blood brain barrier, Acts on GIT; increasing GI motility

Answer 11

Metoclopramide

Side effects: movement disorders (esp. children), fatigue, motor restlessness, spasmodic torticollis, occulogyric crises, menstruation disorders (via effect on prolactin release), Rare Reactions; QT prolongation

Question 12

Example of dopamine receptor antagonist used to treat migraines and cytotoxic therapy-induce emesis

Answer 12

Domperidone (Motilium, Motillium)

side effects: fewer side effects

Question 13

Exampe of serotonin receptor antagonists

Answer 13

Ondansetron

Drug choice for CINV + PONV

Side effects: GI upset, headache

other drugs ending in ‘tron’

Question 14

Example of neurokinin 1 antagonist

Answer 14

• Aprepitant

Side effects: fatigue / listlessness, constipation / diarrhea, loss of appetite, hiccups

Rare Side Effects: dizziness, ringing in the ears, hiccups, dyspepsia, diarrhoea, constipation, anorexia; asthenia, headache..

Question 15

Anti -emetics

Answer 15

Vagal pathway

Vestibular pathway

Vommiting centre

Chemoreceptor trigger zone