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CPT and Prescribing > 19 - Antiemetics > Flashcards

19 - Antiemetics Flashcards

1
Q

What are the physiological steps of vomiting?

A
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2
Q

What are the inputs on the chemoreceptor trigger zone that can activate it and therefore cause vomiting?

A

CTZ is found on the floor of the fourth ventricle on the blood side of the BBB so can interact with toxins and things in the blood

Part of medulla

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3
Q

How can we stop nausea and vomiting?

A

Avoid the triggers or use drugs to target different triggers

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4
Q

What are the two classes of drug that act on the vestibular nuclei as antiemetics?

A
  • Muscarinic receptor antagonists
  • H1 receptor antagonists
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5
Q

How do muscarinic receptor antagonists act as anti-emetics and what are some examples of this class of drug?

A

Hyoscine Hydrobromide (oral or patch)

  • Competitive blockage of muscarinic receptors in the vestibular nuclei and CTZ
  • Antispasmodic
  • Good for people who cannot take tablets, motion sickness and bowel obstruction
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6
Q

What are the side effects of hyoscine hydrobromide?

A
  • Classic anticholinergic side effects
  • Can exploit side effects, e.g long flight motion sickness and sedation for sleep
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7
Q

How do H1 receptor antagonists work as an antiemetic and what are some examples of this type of drug?

A
  • Act centrally on the vestibular nuclei and inhibit histaminergic signals from vestibular system to the CTZ in medulla
  • Good for motion sickness on long journeys
  • Promethazine used for morning sickness
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8
Q

What are the side effects of the class of antiemetic drugs containing cyclizine?

A

H1 receptor antagonist!

  • Cyclizine is the most common antiemetic but cannot be used in old women and children as they are affected most by excitation side effects
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9
Q

What are some classes of antiemetics that work by blocking visceral aferents in the gut?

A

- 5HT3 receptor antagonists

- D2 receptor antagonists

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10
Q

What is the normal function of serotonin in the gut?

A
  • Produced by enterochromaffin cells in response to parasympathetic stimulation
  • Regulates appetite, causes smooth muscle contraction so increased motility and increased gut secretions
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11
Q

How do 5HT3 receptor antagonists work as antiemetics and what are some examples of this type of drug?

A

Ondansetron

  • Acts on visceral afferents in the gut so peripherally reduces GI motility and GI secretions
  • Centrally inhibits the CTZ

- OFTEN FIRST LINE TREATMENT

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12
Q

What are some of the side effects of Ondansetrons and other serotonin receptor antagonists?

A
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13
Q

How do D2 receptor antagonists work as antiemetics (by targeting visceral afferents of the gut) and what are some examples of this type of drug?

A

Domperidone and Metoclopramide (also 5HT3 antagonist)

  • Increases Ach at muscarinic receptors in the gut
  • Promotes gastric emptying by increasing tone of LOS and decreasing tone of pylorus so it opens. Also increased tone of gastric contractions
  • Increases peristalsis
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14
Q

Apart from emesis, what are metoclopramide and domperidone used for?

A

Metoclopramide: GORD and ileus

Domperidone: improving lactation in breastfeeding mothers

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15
Q

What are some side effects of antiemetics from the D2 receptor antagonist class?

A

Metoclopramide: galactorrhoea due to prolactin release, extra-pyramidal effects (e.g dystonia and parkinsonianism)

Domperidone: sudden cardiac death (long QT and VT) so not used very often, galactorrhea

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16
Q

What are some classes of drugs that act directly on the CTZ to prevent/stop vomiting?

A
17
Q

What are some D2 receptor antagonists that act on the CTZ as antiemetics, how do they work and what vomiting situations are they used in?

A

ANTIPSYCHOTICS: chlorpromazine and haloperidol

18
Q

What are some side effects of antipsychotics being used as antiemetics?

A
19
Q

How do corticosteroids act as antiemetics and what are the side effects of these?

A

Dexamethasone and Methylprednisolone

Not used long term so don’t get side effects like skin changes and Cushing’s

20
Q

How do cannabinoids act as antiemetics and what are the side effects of these?

A

Used for chemotherapy last line when everything else has failed!

21
Q

How do neurokinin 1 receptor antagonists act as antiemetic, what else can they be used for and what are some examples of this class of drug?

A

Aprepitant

  • Prevent the excitatory action of substance P at CTZ and in peripheral nerves so can be used as pain killers
  • Good anxiolytic and antidepressant properties
  • Boost effects of serotonin agonists

- Good for chemotherapy delayed emesis

22
Q

What are some side effects of neurokinin 1 receptor antagonists?

A
  • Headache
  • Diarrhoea/Constipation
  • Stevens-Johnson syndrome
23
Q

What drugs are used for motion sickness?

A
  • Trial and error to see what is best and what side effects the patient prefers
  • Take before journey
24
Q

What are some gut problems that can cause nausea and vomiting, and how should we treat this acutely before treating the underlying cause?

A
  • Infective gastroenteritis is supportive treatment as toxin needs to get out
  • Consider a nasogastric tube to decompress
  • Give antiemetic
25
Q

What are prokinetic drugs?

A
  • Drugs that increase gut motility, e.g domperidone and metoclopramide (D2 antagonists)
  • Useful for ileus and GORD
  • Do not use for obstructions as risk of perforation
26
Q

What are the first line anti-emetics?

A

If one not working don’t choose another drug in the same class

27
Q

What is hyperemesis gravidarum and how do we treat it?

A

- Rapid rise in b-hCG stimulates CTZ so severe N+V

  • Higher risk with multiple pregnancies
  • Can cause dehydration, weight loss, electrolyte imbalance
  • May require admission to replace fluids
28
Q

What antiemetics are used for nausea caused by chemotherapy?

A

Patients are risk stratified depending on their chemo drug and dose and then this decides their antiemetic

29
Q

What are some risk factors that increase your chance of post operative nausea and vomiting?

A
30
Q

What antiemetics are used for postoperative nausea?

A
  • Can alter the risk factors, e.g use a different anaesthesia
  • If patient is motion sick use drugs that act on vestibular nuclei e.g H1 receptor antagonists
  • If patient is having gut surgery use drugs that act on visceral afferents from the gut e.g 5HT3 antagonists and D2 receptor anatagonists
31
Q

What drugs can we use to treat diarrhoea?

A
  • Antimotility drugs (opioid agonists)

- Loperamide (u) and Codeine Phosphate (u and d)

  • Loperamide is 1st line as gut specific
32
Q

What are the side effects of using u opioid agonists to treat diarrhoea?

A
  • Paralytic ileus
  • Nausea and Vomiting
  • Sedation
  • Addiction (codeine)
33
Q

What diet can you recommend to someone with long term loose stools, e.g IBS, short bowel, drug side effects?

A

CONSTIPATING DIET

34
Q

What lifetsyle changes can you recommend to someone with constipation?

A
  • Drink more water
  • Increase fibre intake e.g fruit, veg, nuts
  • Regular exercise
  • Toilet routine and positioning
35
Q

What are some different drugs used for constipation?

A
36
Q

What are some examples of osmotic laxatives and what is their mechanism of action?

A

- Lactulose: draws fluid in from outside the gut

- Macrogol (really good - up to 12 sachets a day): retain the fluid they came with

  • MOVICOL FIRST LINE: both increasing amount of water in large bowel
37
Q

What are some examples of stimulant laxatives and how do they work?

A

- Bisacodyl, Docusate Sodium, Glycerol Suppository, Senna

- Enhance gut motility and increase water and electrolyte transfer into the lower gut

  • Given orally or rectally when osmotics haven’t worked
38
Q

What are some examples of bulk-forming laxatives and how do they work?

A

- Ispaghula Husk and Methylcellulose

  • Stimulation through increase faecal bulk, hydrophillic action causing gut lumen water retention
39
Q

How do stool softeners work to relieve constipation and what are some examples?

A

Like washing up liquid changing the surface tension!!!

CPT and Prescribing (25 decks)

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