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Pharmacology > Antiemetics and Antidiarrhoeals > Flashcards

Antiemetics and Antidiarrhoeals Flashcards

1
Q

Define vomiting

A

Involuntary, forceful ejection of gastric contents through the mouth.

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2
Q

Describe the steps to vomiting.

A
  • Process initiated by the vomiting centre (area postrema) in the medulla.
  • Nausea, salivation and sweating occurs.
  • Reverse peristalsis in upper small bowel.
  • Deep inspiration
  • Closure of glottis.
  • Abdominal muscles contract.
  • Lower oesophageal sphincter relaxes.
  • Emesis occurs.
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3
Q

Name some inputs to the chemoreceptor trigger zone?

A

Sensory (somatic) afferents via midbrain. Response to emotional/visual stimuli/ olfactory stimuli.
Direct triggers by certain drugs.
Visceral afferents from gut (e.g. in gastroenteritis).
Vestibular nuclei (motion sickness).

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4
Q

Motion sickness.

A

This is an imbalance between inputs from visual pathways (I am reading a book and thus I must be still) and the vestibular pathways (sensing movement and inertia).

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5
Q

Drugs that act on vestibular nuclei.

A

Anti-muscarinics such as Hyoscine and H1 receptor antagonists such as cyclizine and diphenhydramine. Both of these drugs also have actions on the CTZ.

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6
Q

What are some of the side effects of Hyoscine?

A

It causes drowsiness and memory problems. Can worsen glaucoma and cause a dry mouth and constipation (most secretory functions are under parasympethetic control).

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7
Q

Give one advantageous route of Hyoscine administration.

A

It is avaliable as a transdermal patch which is good for people who cannot swallow tablets.

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8
Q

Give two indications for H1 receptor agonists and a particularly useful drug in these cases.

A

Motion sickness on long plane journeys (cyclizine/diphenhydramine also typically sedate).
Morning sickness in pregnancy (Promethazine not too harmful for baby).

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9
Q

Why would cyclizine be a bad idea in a small, elderly person or a child?

A

Can cause either severe drowsiness or paradoxical excitation.

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10
Q

List some side effects of the H1 receptor antagonists.

A

Sedation/excitation.
Antimuscarinics so cause dry mouth, constipation and maybe even urinary retention.
Can cause long QT related cardiotoxicity.

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11
Q

What is the role of serotonin in the gut?

A

95% of the body’s serotonin is in the gut. It is released following parasympethetic stimulation and promotes peristalsis and increases gut secretion. It also has a role to play in regulating appetite.

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12
Q

Where in the gut is serotonin produced?

A

Enterochromaffin cells.

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13
Q

Give an example of a 5HT3 receptor antagonist?

A

Ondansetron - this is one of the most commonly used anti-emetics.

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14
Q

Describe the effects of ondansetron on the gut and CTZ?

A

Inhibition of CTZ.

At gut, it decreases motility and secretions.

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15
Q

Give some side effects of Ondansetron.

A
  • Long QT
  • Constipation
  • Headache.
  • Extra pyramidal side effects (e.g. dystonia and Parkinsonism).
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16
Q

Give some common D2 receptor antagonists and suggest indications for them. There should be two.

A
  • Metaclopramide - a useful prokinetic in ileus and for GORD.
  • Domperidone - useful in nausea relating to Parkinson’s drugs such as the dopamine receptor agonists.
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17
Q

What effects does Metaclopramide have on the stomach.

A

It increases LOS tone, hopefully preventing reflux, it increases gastric contractions and promotes pyloric opening. This should cause gastric emptying.

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18
Q

What are some adverse effects of Metaclopramide?

A

Can cause galactorrhoea and extra-pyramidal side effects.

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19
Q

How could Domperidone help a breastfeeding mother?

A

Increases prolactin secretion.

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20
Q

What evidence has come to light to decrease the use of Domperidone significantly?

A

It has been linked to sudden cardiac death via QT prolongation.

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21
Q

Give some example of D2 receptor antagonists that act on the CTZ alone, not the gut.

A

The ‘zines’. These are old fashioned antipsychotics.

Haloperidol, chlorpromazine, levomepromazine. These are very useful in chemotherapy and palliation.

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22
Q

Give a side effect of typical antipsychotics that makes them useful in palliative care.

A

They are heavily sedating and act to calm people experiencing terminal agitation.

23
Q

Give a concerning side effect of treatment with -promazines.

A

They can cause hypotension.

24
Q

Are corticosteroids used as anti-sickness drugs?

A

Yes. Dexamethasone and methylprednisolone are good examples. They are good for PONV, chemotherapy and palliation and have the ‘happy’ side effect of promoting appetite and raising blood sugar.

25
Q

What is a significant side effect of steroids as anti-emetics?

A

They can cause insomnia.

26
Q

Give an example of a drug that is used as last line in chemotherapy associated nausea and vomiting? What side effects can it cause.

A

Nabilone - a synthetic cannabinoid. It can cause diziness and drowsiness.

27
Q

Give an example of a ‘neurokinin 1 receptor antagonist’ and explain what they do.

A

Aprepitant - it prevents the action of Substance P at the CTZ and works synergistically with the 5HT3 receptor antagonists. It is particularly good when used in preparation for delayed vomiting in chemotherapy.

28
Q

Give some side effects of Aprepitant (a neurokinin 1 receptor antagonist)

A

Can cause diarrhoea, headache and - most seriously - SJS.

29
Q

What extra effects does midazolam have peri-operatively?

A

It is thought to have some effects on the GABA receptor at the CTZ, adding anti-emesis to its anxiolytic properties.

30
Q

As well as promethazine, give another drug that is good in morning sickness / hyperemesis gravidarum.

A

Gabapentin.

31
Q

When may a naso-gastric tube come in handy?

A

If nausea is caused by stomach distension an NG tube can limit stimulation of the visceral afferents by draining a distended stomach.

32
Q

What commonly avaliable item is a useful adjunct to metaclopramide in managing ileus?

A

Chewing gum! Sensation of chewing and the taste increases vagal tone to the bowels, starting to overcome the ileus.

33
Q

In what circumstances is it bad to use prokinetics (or stimulant laxatives for that matter).

A

Bowel obstruction/ risk of perforation.

34
Q

First and Second Line Anti Emetics in Primary Gut Problems

A

1) Ondansteron and or Cyclizine

2) Dexamethasone

35
Q

Which hormone causes hyperemesis gravidarum and when do symptoms peak?

A

Caused by high levels of beta-hCG. It occurs in weeks 4-16 of pregnancy but may continue beyond this. It is extremely debilitating and women can lose weight, become dehydrated and even suffer from electrolyte imbalances.

36
Q

First, second and third line drugs for hyperemesis gravidarum.

A

1) Promethazine (H1 receptor antagonist)
2) Metaclopramide (D2 receptor antagonist)
3) Ondansetron (5HT3 receptor antagonist)

37
Q

Core antiemetics in chemotherapy.

A

Guidelines differ but dexamethasone is widely used as a base agent. It is the only one routinely given if risk of emesis is low and it combined with ondansetron in moderate risk and ondansetron + aprepitant in high risk cases.

38
Q

What is a common ‘ rescue ‘ antiemetic in chemotherapy?

A

Metaclopramide

39
Q

Give some risk factors for PONV

A 
Female.
Non smoker
Inhalational agents used.
General anaesthesia. NO2 used. 
Younger age.
PONV history.
Long surgery.
Laparoscopic surgery. 
Post op-opioids.
40
Q

Managing PONV risk.

A

In low risk cases we can just write up a PRN anti-emetic. In much higher risk cases it is best to give 1-3 anti-emetics as precaution. It is easier to stop sickness before it starts than stop it once established.

41
Q

Opioid Receptor Agonists in Diarrhoea.

A
  • Loperamide - has no systemic mu agonist effects.
  • Codeine - systemic mu agonist.
  • Morphine - specific mu agonists.
42
Q

How do opioids work in slowing diarrhoea or inducing constipation?

A

Decreases peristalsis by acting on mu opioid receptors in myenteric (Auerbach’s) plexus. This decreases the tone of the peristaltic muscle, increasing contact time for water absorption and decreases colonic mass movement by suppressing gastro colic reflex.

43
Q

When used for pain, what adverse effects can codeine and morphine have?

A

They can cause paralytic ileus as well as N+V. They are also sedative and addictive.

44
Q

What could cause chronically loose stools?

A

IBS, IBD, short bowel syndrome, drug side effects.

45
Q

What diet could you recommend to improve loose stools.

A

Limiting fruit to 3 portions a day. No sorbitol, caffeine, fizzy drinks. White rice, bread and pasta, banannas. You could consider probiotics to re-balance intestinal flora.

46
Q

What lifestyle changes could you put in place to manage constipation?

A

Drink more water.
Increase fibre intake (wholegrain foods, fruit and veg)
Increase exercise
Establish toilet routine end encourage people to raise their feet on a stool to optimise the position of the pubo-rectalis muscle.

47
Q

How does lactulose work?

A

Osmotic laxative, draws in water.

48
Q

How do macrogols (e.g. movicol) work.

A

Often packaged with electrolytes. Movicol = Macrogol 3350 + electrolytes). These retain the water they come with. They are dispensed as powder that has to be mixed with water.

49
Q

Give an example of a stimulant laxative and state how it works?

A

Bisacodyl. Acts to increase intestinal motility. Senna and sodium picosulphate are other examples.

50
Q

Give a common stool softener and state its other properties?

A

Docusate sodium - also works as a stimulant laxative.

51
Q

How does a glycerin suppository work to trigger a bowel movement?

A

It irritates the rectum to trigger mass movement and lubricates the passage of the stool out.

52
Q

What are bulk forming laxatives?

A

Examples include Ispaghula husk and methylcellulose. They to increase the ‘bulk’ of the stool (replacing fibre effectively) so peristalsis has something to push against.

53
Q

Not including oral docusate sodium, give one route of administration for a stool softener.

A

Arachis oil enema.

Liquid parrafin PO.

Pharmacology (10 decks)

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