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S4 Pharma CPT > Antiemetics > Flashcards

Antiemetics Flashcards

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1
Q

Difference between vomiting & regurgitation

A

Vomiting - involuntary forceful expulsion of gastric contents through mouth

Regurgitation - effortless bringing up of things that have not yet reached stomach or passive overflow stomach contents

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2
Q

What’s the sequence of steps that triggers vomiting?

A 
Vomiting centre in medulla signals to vomit -> 
Nausea, salivation, sweating -> 
Retrograde peristalsis -> 
deep inspiration -> 
closure of glottis (if not choke)-> 
Abdo muscles contract -> 
LOS relaxes
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3
Q

What triggers the vomiting centre/ chemoreceptor trigger zone? Where is it?

A
  • sensory afferents via midbrain
  • vestibular nuclei (motion sickness, vertigo)
  • visceral afferents from gut (mainly through vagus N)
  • direct triggers (drugs/ hormones/ toxins in blood as blood side of BBB)

In medulla on floor of 4th ventricle, blood side of BBB

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4
Q

How do muscarinic receptor antagonists work? Give an example. Side effects

A

Competitive blockade of muscarinic Ach receptors in vestibular nuclei + chemoreceptor trigger zone

E.g. Hyoscine hydrobromide

Uses: can’t take tablets - patch, motion sickness, bowel obstruction, good for agitation (sedation), good for diarrhoea (constipation)

Side effects (receptors all over body, part of parasympathetic NS): sedation, memory Problems, glaucoma, dry mouth & constipation

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5
Q

How do H1 receptor antagonists (anti-histamines) work? Give examples. Uses and side effects.

A

Centrally - acts on vestibular nuclei, inhibits histaminergic signals from vestibular system to CTZ in medulla

E.g. cyclizine, levomepromazine, diphenhydramide

Uses: motion sickness - long plane journeys, promethazine - morning sickness

Cyclizine - not suitable for little old ladies or children <6yrs

Side effects: sedation, excitation, antimuscarinic - dry mouth, constipation, urinary retention, cardiac toxicity (long QT interval)

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6
Q

How is serotonin used in the gut?

A

95% serotonin in the body is located in the gut produced by enterochromaffin cells

PS stimulation -> serotonin excites enteric neurones -> Sm contraction increases motility (except in stomach), increases gut secretions, regulates appetite

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7
Q

How do 5HT3 receptor antagonists work? Give examples. Uses and side effects.

A

5HT = serotonin

Peripherally - reduces GI motility/ secretions

Centrally - inhibits CTZ

E.g. Ondansetron - common.
granesitron/ palonosetron - niche/ palliative/ oncology

Uses: good for almost everyone (often 1st line)

Side effects (uncommon): constipation, headache, elevated liver enzymes, long QT syndrome, extra pyramidal effects (dystopia, Parkinsonism)

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8
Q

How does metoclopramide work? Uses and side effects.

A

D2 receptor anatagonist

Metoclopramide increases Ach at muscarinic receptors in gut -> promotes gastric emptying, increases tone LOS closes, increases tone/ amplitude gastric contractions, decreases tone pylorus opens, increases peristalsis

Uses: GORD, Ileus (normal gut movement lost e.g. post op, infection)

Side effects: galactorrhoea via prolactin release, extra pyramidal effects (dystopia, Parkinsonism)

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9
Q

How does domperidone work? Uses and side effects

A

D2 receptor antagonist

Similar mechanism to metoclopramide, not used much anymore due to cardiac side effects

Uses: improving lactation breastfeeding mothers

Side effects: sudden cardiac death (long QT and VT), galactorrhoea (increases prolactin)

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10
Q

D2 (dopamine) receptors antagonists acting on the CTZ, how do they work? Give examples, uses and Side effects

A

The ‘zines’ act on CTZ, May also block H1 muscarinic receptors

E.g. prochlorperazine, chlorpromazine, haloperidol

Uses: motion sickness, vertigo,
Prochlorperazine in pregnancy, haloperidol (CTZ) chemotherapy & palliation

Side effects: extra pyramidal effects (dystonia, parkinsonism), sedation, hypotension

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11
Q

How do corticosteroids work to prevent vomiting? Give examples, uses and side effects

A

Act on CTZ

E.g. dexamethosone, methylprednisolone

Assumed act on CTZ, May also properties D2 receptor antagonists

Uses: perioperative nausea & vomiting, chemotherapy and palliation

Side effects: insomnia, increased appetite, increased blood sugar

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12
Q

How do cannabinoids work? Give an example, uses and side effects

A

Synthetic compounds assumed to act on the CTZ

E.g. Nabilone

Good for chemotherapy as last line

Side effects: dizziness, drowsiness

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13
Q

How do neurokinin 1 receptor antagonists work, give examples, uses and side effects?

A

Act on CTZ

Prevent action of substance P at CTZ and in peripheral nerves (painkillers), boosts effects of 5HT3 receptor antagonists, anxiolytic (reduces anxiety) + antidepressant properties

E.g. aprepitant, fosaprepitant, netupitant

Good for chemotherapy particularly delayed emesis

Side effects: headache, diarrhoea/ constipation, stevens- Johnson syndrome (rare, serious disorder of skin)

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14
Q

Best methods to treat motion sickness?

A

Prevention is better than cure - take before journey

1st line: Hyoscine hydrobromide - sedating

If driving/ need to concentrate: connirazine - fewer side effects

Trial & error

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15
Q

What are prokinetics useful for? Give examples. When should you use them?

A

Increase gut motility

E.g. Domperidone, metoclopramide

Uses: GORD, ileus (gum may help first)

Don’t use: obstruction, risk of perforation

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16
Q

What should you consider trying before medication for a lot of gut pathology if they are being sick?

A

A nasogastric tube - mechanical decompression of the stomach

17
Q

What antiemetics are used normally for gut pathology bar prokinetics?

A

1st ondansetron (5HT3 receptor antagonist)

&/ or cyclizine (H1 R antagonist - not old ladies/ children)

Then add: dexamethasone if needed (corticosteroid)

Different classes

18
Q

What is hyperemesis gravidarum?

A

V severe morning sickness

Rapid rise beta- hcg-> stimulates CTZ
Typically weeks 4-16
Higher risk with multiple pregnancies

Dehydration, weight loss, electrolyte imbalance, urinary ketones

19
Q

Treatment of hyperemesis gravidarum

A

Promethazine (H1 R antagonist) Or prochlorperazine (D2 R antagonist)

Then add: metoclopramide (D2 R antagonist)

Then add: ondansetron (5HT3 R antagonist - 1st trimester risk cleft lip/ palate)

20
Q

Treatment of emesis in chemotherapy

A

Low risk chemo: dexamethasone (if needed + metoclopramide)

Moderate: dexamethasone & ondasetron (+ metoclopramide)

High risk: dexamethasone & ondansetron & aprepitant (+ metoclopramide)

Dexamethasone - corticosteroid
Ondansetron - 5HT3 R antagonist
Aprepitant - NK1 antagonist
Metoclopramide - D2 R antagonist

21
Q

Risk factors for post- operative nausea & vomiting

A

Female

History of PONV/ motion sickness

Younger

Non smoker

Genera anaesthetic

Volatile anaesthetic gases/ NO

PO opioids

Longer op

Laparoscopic surgery

22
Q

Post- op N&V treatment

A

Low risk: wait and see

Moderate: pick 1/ 2 antiemetic agents

High: 3+ agents

If prophylaxis fails use antiemetic of different class

23
Q

What do you use to treat infective gastritis?

A

Osmotic or secretory agents

24
Q

Give examples of opioid receptor agonists, how do they work

A

Loperamide - specific to mu receptors in myenteric plexus

Decreases tone longitudinal/ circular SM, reduces peristalsis but increases segmental contractions, decreases colonic mass movement by suppressing gastrocolic reflex

Works just in the gut

Max effects in 24hrs

Also: codeine, morphine - mu and delta receptors - similar effects, more often used wine patients also have pain

Works all over body

25
Q

Side effects of opioid receptor agonists

A

Paralytic ileus

N&V

Sedation

Addiction (codeine & morphine)

26
Q

For those with long term loose stools what should they consider adding and limiting from their diet?

A

E.g. IBS, IBD, short bowel, hypermotility, drug side effects

The constipating diet:
Bananas, white rice, white bread/ pasta

Limit fruit 3per day
Avoid: caffeine, sorbitol, fatty/ spicy foods, fizzy drinks

Consider probiotics

27
Q

Lifestyle/ diet changes for those with chronic idiopathic constipation?

A

More water

Increase fibre: whole grain foods, f&v, nuts, pulses

Regular exercise

Toilet routine and positioning

Consider probiotics

28
Q

Categorise the medications for constipation

A

Laxatives - orally - osmotic, stimulants, bulk forming, stool softeners

Enemas - rectally - osmotic, stimulants

29
Q

Give examples of osmotic laxatives, how do they work?

A

Lactulose (draws H2O in, mild constipation),

1st line: movicol (retains H2O, up to 12 sachets a day, bad constipation),

cosmocol (retains H2O)

Increases water in large bowel

30
Q

Give examples of stimulant laxatives, how do they work?

A

Bisacodyl

Dosimeter picosulphate

Senna

Docusate sodium - stimulant & stool softener

Glycerine - rectal irritation & lubrication & stool softener

If need more help, increase intestinal motility, orally or rectally

31
Q

Give examples of bulk forming laxatives, how do they work?

A

Ispaghula husk

Methylcellulose

Medicinal fibre - sometimes also helpful for diarrhoea

Ideally just get from diet or increase H2O

32
Q

Give examples of stool softeners, how do they work?

A

Docusate sodium - stimulant

Glycerine - rectal irrational, lubrication, stimulant

Liquid paraffin

Decrease surface tension of stool

Increase penetration of fluid into stool

S4 Pharma CPT (22 decks)

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