Anti-emetics

Question 1

Define emesis.

Answer 1

Physical event; forceful evacuation of gastric contents through the mouth. A protective mechanism in response to something harmful being ingested.

Question 2

What are the stages of emesis?

Answer 2

Feeling of nausea, retching, vomiting.

Question 3

What can emesis be caused by?

Answer 3

Disease states such as migraine, bacterial and viral infections. Pregnancy, motion sickness. Side effects of drugs such as chemotherapy and post-op.

Question 4

What is the vomiting reflux regulated by?

Answer 4

CNS (medulla). “Brainstem emetic control center”

Question 5

What are the 3 inputs of the emetic control center?

Answer 5

The Chemorecpetor Trigger Zone, The Vagal Pathway, The Vestibular Pathway.

Question 6

What is the chemoreceptor trigger zone?

Answer 6

Associated with substances, toxins and drugs - sensitive to chemicals. Main site of action of antiemetic drugs.

Question 7

What is the vagal pathway?

Answer 7

Associated with sensory input (pain, smell, sight, thought). Stimuli from the pharynx and GI tract.

Question 8

What is the vestibular pathway?

Answer 8

Disorientating motion.

Question 9

List the neurotransmitters involved in the blockade during the the emesis response.

Answer 9

serotonin, ACh, dopamine, substance P, histamine, enkephalin.

Question 10

What are H1 antagonists?

Answer 10

Act on vomiting centre and the vestibular pathway, act on histamine. Used in emesis caused by motion sickness, vestibular disease and Gi irritants.

Question 11

Name the H1 antagonists?

Answer 11

Cyclizine, Cinnarizine, Promethazine

Question 12

What are the side effects of H1 antagonists?

Answer 12

Drowsiness and sedation

Question 13

What are histamine receptor agonists?

Answer 13

H3 agonists. E.g Betahistine Hydrochloride. Used for vertigo. Activates H-receptors on blood vessels in the inner ear.

Question 14

What are muscarinic receptor antagonists?

Answer 14

General purpose anti-emetics. Used in motion sickness. Act on Vomiting centre and vestibular pathway.

Question 15

What are the types of muscarinic receptor antagonists?

Answer 15

Hycosine and Scopolaimine.

Question 16

What are the side effects of hycosine and scopolaimine?

Answer 16

Dry mouth, blurred vision

Question 17

What do dopamine receptor antagonists act on?

Answer 17

Act on D2 receptors in the chemoreceptor trigger zone. Can treat emesis caused by uraemia, opioids, Gi disorders, viral infections.

Question 18

What is Phenothiazines?

Answer 18

D2 receptor antagonist/ Used in severe morning sickness. Iv, oral or suppository.

Question 19

What are the side effects of phenothiazines?

Answer 19

Sedative, hypotension, dystonia

Question 20

What is metoclopramide?

Answer 20

D2 receptor antagonist. Increases GI motility. Oral/IM/IV.

Question 21

Side effects of metoclopramide?

Answer 21

Movement disorders, fatigue, motor restlessness, mentruation disorders

Question 22

What is Domperidone?

Answer 22

D2 antagonist. Has reduced central effectiveness but less side effects. Used for migraine and cytotoxic therapy induced emesis.

Question 23

What do serotonin receptor antagonists act on?

Answer 23

5HT3 antagonists - serotonin. Act on chemoreceptor trigger zone and vagal pathway. Treat emesis caused by chemo, anaesthetics, and radiation.

Question 24

What is the serotonin antagonist of choice?

Answer 24

Ondansetron. Side effects = headache an GI disturbances.

Question 25

What are NK1R antagonists?

Answer 25

Act on substance P receptors. Active in late phase emesis with cytotoxic drugs.

Question 26

Name a NK1R antagonist drug.

Answer 26

Aprepitant.

Question 27

Side effects of aprepitant?

Answer 27

fatigue, constipation/diarrhoea, loss of appetite, hiccups. dizziness, dyspepsia, anorexia.

Question 28

Which corticosteroid can treat emesis caused by chemotherapy?

Answer 28

Dexamethasone.