Antiemetics & Antidiarrhoeals Flashcards

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1
Q

What is hyperemesis gravidarum?

A

Not just morning sickness, but also involves dehydration, weight loss, electrolyte imbalance and urinary ketones. It’s caused by the rapid rise in beta hcg, which stimulates the CTZ.

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2
Q

What is the difference between vomiting and regurgitation?

A

Vomiting is a forceful expulsion, regurgitation is not forceful and is due to mechanical problems at the lower end of the oesophagus.

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3
Q

Name 4 things that can trigger the chemoreceptor trigger zone (CTZ).

A
  • vestibular nuclei - receive signals from inner ear and semicircular canals
  • direct triggers e.g. Drugs/hormones
  • sensory afferents e.g. Sight/taste/smell
  • visceral afferents from gut due to damage or inflammation
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4
Q

Describe the process of vomiting.

A
  • CTZ is triggered
  • retrograde peristalsis in gut
  • deep inspiration
  • closure of glottis
  • abdominal muscles contract
  • lower oesophageal sphincter relaxes
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5
Q

Name 2 drug classes that act on the vestibular nuclei.

A
  • mAChr antagonists

- H1 antagonists

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6
Q

Name 2 drug classes that act on the visceral afferents in gut.

A
  • 5HT3 antagonists

- D2 antagonists

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7
Q

Name all the drug classes that act directly on the CTZ (7).

A
  • mAChr antagonists
  • H1 antagonists
  • D2 antagonists
  • 5HT3 antagonists
  • corticosteroids
  • cannabinoids
  • NK1 antagonists
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8
Q

Name a mAChr drug used as an antiemetic.

A

Hyoscine hydrobromide - used for motion sickness.

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9
Q

What are the typical anticholinergic side effects of drugs?

A

Constipation

Dry mouth

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10
Q

Name 2 H1 receptor antagonists used as antiemetics.

A

Cyclizine

Promethazine

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11
Q

What is promethazine and what is it often used for?

A

H1 antagonist - used for motion sickness, but especially morning sickness during pregnancy.

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12
Q

Why should you be careful when prescribing cyclizine?

A

Has side effects of sedation and excitement - these side effects can be very prominent in old ladies and children who are smaller.

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13
Q

Name a 5HT3 antagonist used as an antiemetic.

A

Ondansetron

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14
Q

Which cells produce serotonin?

A

Enterochromaffin cells in response to parasympathetic stimulation.

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15
Q

Name 2 D2 antagonists that act directly on the visceral afferents of the gut.

A

Metacloperamide

Domperidone

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16
Q

What is the MOA of metacloperamide and domperidone?

A

D2 antagonists - block D2 receptors in gut, speeding up stomach emptying, can be useful for GORD or ileus.

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17
Q

Name a side effect of metacloperamide and domperidone.

A

-galactorrhoea (inappropriate/excessive production of milk)

18
Q

Name 2 D2 antagonists that act directly on the CTZ.

A

Chlorpromazine

Haloperidol

19
Q

What is haloperidol used for?

A

Often used for chemotherapy and palliative care as it is slightly sedative, so can help patients to relax.

20
Q

Name a corticosteroid used as an antiemetic.

A

Dexamethasone

21
Q

What is dexamethasone used for?

A

Palliative care
Chemotherapy
Perioperative nausea

22
Q

Name a cannabinoid used as an antiemetic.

A

Nabilone

23
Q

Name a neurokinin 1 receptor antagonist used as an antiemetic.

A

Aprepitant

24
Q

Name 2 things that the D2 antagonists chlorpromazine and haloperidol can be used for.

A

Antipsychotics

Antiemetics

25
Q

What is the MOA of NK1 antagonists?

A

Prevents the action of substance P at the CTZ, acts as an antiemetic.

26
Q

Name a side effect of aprepitant.

A

Stevens Johnson Syndrome

27
Q

What is Stevens Johnson Syndrome?

A

A condition that is a disorder of the immune system, but is often triggered by drugs or infections (type IV hypersensitivity reaction). Starts with a severe skin reaction, fever and flu-like symptoms. Can lead to blindness.

28
Q

What drugs are used for GORD or ileus?

A

Domperidone or metacloperamide (not suitable for obstruction).

29
Q

What is the specific treatment for gut problems e.g. Ileus, obstruction, appendicits, cancer, GORD?

A

Ondansetron
And/or cyclizine
Then add dexamethasone

30
Q

What is the specific drug treatment for hyperemesis gravidarum?

A

Promethazine or prochlorperazine
Then add metacloperamide
Then add ondansetron

31
Q

What specific drug treatment can be used for chemotherapy sickness?

A

Dexamethasone
Then add ondansetron
Then add aprepitant
Use metacloperamide for rescue

32
Q

What drugs can be used for post-operative nausea and vomiting?

A

Pick 1 or 2 antiemetics (any).

33
Q

Name the 2 types of diarrhoea.

A

Osmotic - due to reduced absorption there is excess osmotic material in gut.
Secretory - excess secretion of ions into gut lumen.

34
Q

Name 3 opioid receptor antagonists used for diarrhoea.

A

Loperamide
Codeine
Morphine

35
Q

How do opioids treat diarrhoea?

A

Reduce peristalsis and slow down gut movement, allowing more time for water absorption.

36
Q

What lifestyle modifications can help relieve constipation.

A
  • more fibre in diet - ‘constipation diet’
  • drink more water
  • more exercise
37
Q

What are the 3 types of laxatives that can be used for constipation?

A
  • osmotic
  • stimulant
  • bulk forming
38
Q

Name 2 osmotic laxatives and explain their MOA?

A

Lactulose, macrogol

Contain sugar that osmotically draws fluid into the gut.

39
Q

Name 2 stimulant laxatives and explain their MOA.

A

Docusate sodium, senna

Increase intestinal motility and increase water and electrolyte transfer into the gut.

40
Q

What is the MOA of bulk forming laxatives?

A

Increase faecal bulk, causing increased water retention in the gut lumen (fibre keeps liquid in the stool).

41
Q

How do stool softeners work?

A

Lubricate and break down stool, aids passing.

42
Q

How do enemas work?

A

Decrease surface tension of stool and increases penetration of fluid into stool