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LCRS Pharma > Anti-emetics > Flashcards

Anti-emetics Flashcards

1
Q

what is nausea?

A

subjective, unpleasant sensation in the throat and stomach; often precedes vomiting.

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2
Q

what is vomiting?

A

forceful propulsion of stomach contents out of the mouth.

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3
Q

what precedes nausea and vomiting?

A

salivation, sweating and increased heart rate.

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4
Q

describe the physiological vomiting pathway

A

o Deep breath, glottis closes and the larynx rises to open the upper oesophageal sphincter. Soft palate elevates.
o Diaphragm contracts sharply to create a negative intrathoracic pressure to facilitate sphincter opening.
o Whilst diaphragm contracts, abdominal walls contract to squeeze the stomach and raise intra-gastric pressure. With the pylorus closed and the upper sphincters open, pressure escapes proximally.

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5
Q

what are the consequences of acute and chronic nausea?

A

o Acute nausea – interferes with mental/physical activity.

o Chronic nausea – very debilitating.

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6
Q

what are the consequences of severe vomiting?

A

1) Dehydration.
2) Hypochloraemic metabolic alkalosis (Loss of gastric HCl)

3) hypokalaemia.
(Reduction in renal HCO3- excretion / increased reabsorption–> increased sodium reabsorption and potassium excretion)

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7
Q

where is the vomiting centre located?

A

the area postrema specifically is located in the medulla of the brainstem

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8
Q

where is the chemoreceptor trigger zone located?

A

in the medulla

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9
Q

what is significant about the location of the vomiting centre and the CTZ?

A

they have very porous BBBs

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10
Q

what cranial nerves are involved signalling vomiting?

A

CN IX and X

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11
Q

what system is involved in motion sickness (children particularly)?

A

vestibular system (labrinyth)

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12
Q

what are some causes of nausea and vomiting?

A
  • chemotherapy e.g. cisplatin
  • motion sickness
  • gastroparesis
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13
Q

how does cisplatin induce nausea and vomiting?

A
  • cisplatin is toxic to enterochromaffin cells that line the GIT
  • damage leads to the release of free radicals
  • there is excess 5HT release which activates the CTZ by binding to its 5HT3a receptors
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14
Q

what does 5HT bind to in the CTZ to induce nausea and vomiting?

A

5HT3a receptors (ligand gated ion channel)

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15
Q

what is the treatment option for chemotherapy induced vomiting?

A

Ondansetron (serotonin receptor antagonist)

given as triple therapy with cortiocosteroids e.g. glucocorticoids and aprepitant (neurokinin-1 receptor antagonist)

o Preventing anti-cancer drug-induced vomiting.
o Radiotherapy-induced sickness.
o Post-operative nausea and vomiting.

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16
Q

what is ondansetron? what does it do?

A

Serotonin (5-hydroxytryptophan) receptor antagonists
–> 5-HT3a

  • Blocks transmission in visceral afferents (vagus and splanchnic nerves) that use serotonin receptors
  • primary site: CTZ and GIT
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17
Q

why is ondansetron given with glucocorticoids at times?

A

serotonin receptor antagonist:
to have an anti-inflammatory effect
reduce the production of free radicals
use for anti-cancer drugs like cisplatin

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18
Q

why is ondansetron given as triple therapy?

A

anti-cancer treatment e.g. chemotherapy induced nausea and vomiting is biphasic

ondansetron is used to treat the first stage while the other 2 drugs are used to treat the second stage

19
Q

describe ondansetron pharmacokinetics

A

Oral (well absorbed, excreted in urine)

– needs good renal function

20
Q

what are some unwanted side effects of ondansetron?

A

o Headache.
o Sensation of flushing and warmth.
o Constipation – increased large bowel transit time.

21
Q

how does motion sickness induce nausea and vomiting?

A
  • there is a labyrinthine neuronal mismatch leading to the activation of H1 receptors
  • these histamine receptors on the vestibular nuclei
  • they have an afferent to the CTZ which bind to muscarinic receptors on the CTZ
  • N&V induced
22
Q

what is the treatment option for motion sickness induced nausea and vomiting?

A

promethazine and/or hyoscine

promethazine (H1 antagonist)used in:
o Motion sickness 
– used prophylactically normally.
o Disorders of the labyrinth
 – i.e. Meniere’s disease.
o Hyperemesis gravidarium 
– a complication of pregnancy.
o Pre- and post-operatively. 
o relief of allergy, combat anaphylaxis, night sedation.

hyoscine can be used in pre-operative medication.

23
Q

what is promethazine?

- order of potency

A

Mixed receptor antagonist: phenothiazine derivative
Consider it as H1 antagonist
o Potency on receptors: H1>M>D2.

o other phenothiazines can have greater antagonistic effects on D2 to acts as neuroleptics.

24
Q

describe the pharmacokinetics of promethazine

A

o Administration= Oral.
o Onset of action= 1-2 hours - Maximum effect at 4 hours.
o Duration of action= 24 hours.

25
Q

what are the unwanted side effects of promethazine?

A
  • Dizziness.
  • Fatigue.
  • Sedation
  • Anti-muscarinic effects.
  • Tinnitus.
  • Excitation in excess
  • Convulsions.
26
Q

what is hyoscine?

  • order of receptor potency
  • systems it acts on
A

non-selective muscarinic receptor antagonist
mainly for motion sickness

o Antagonistic potency order:
Muscarinic >>> D2/H1.
o Acts centrally:
- vestibular nuclei--> , mAChR, H1 MAIN
- CTZ --> D2
- vomiting centre-->mAChR,H1
27
Q

when should hyoscine be given?

A

as Prophylaxis:

before nausea has been established (has little effective after nausea is established) therefore preoperatively

28
Q

describe the pharmacokinetics of hyoscine

A

Muscarinic receptor antagonist

  • peak effect in 1-2 hours
  • oral, trans-dermal.
29
Q

what are the unwanted side effects of hyoscine?

A
  • Drowsiness
  • Dry mouth
  • Cycloplegia – paralysis of ciliary muscles.
  • Mydriasis
  • Constipation
30
Q

what is gastroparesis?

A

delayed stomach emptying due to reduced contractions

31
Q

how does gastroparesis induce nausea and vomiting?

A
  • release of 5HT (serotonin)
  • activates 5HT3aR on the CTZ
  • N&V via D2 receptors on CTZ
32
Q

what is the treatment option for gastroparesis induced nausea and vomiting?

A

Metoclopramide, Domperidone (D2 antagonists)

these have pro-kinetic effects

33
Q

what are Metoclopramide and Domperidone?

  • potency order
  • system target
  • additional effect
A

D2-Receptor Antagonists

oAntagonistic potency order:
D2&raquo_space; H1&raquo_space;> muscarinic receptors.
o Acts centrally, especially on the CTZ.

o Pro-kinetic effects in the GI tract – i.e. effects of PNS

34
Q

what is the benefit of using D2 receptor antagonists like metoclopramide in gastroparesis?

A

Has pro-kinetic effects in the GI tract:

  • Increase SM motility
  • accelerate gastric emptying
  • accelerate transit through tract
  • Less to vomit.
35
Q

why do D2 receptor antagonists acting on the CTZ not treat motion sickness?

A

Vestibular system puts direct input into the vomiting centre

blocking H1 would be most effective in this case

36
Q

what are the use of metoclopramide?

A

D2 antagonist

o Uraemia – due to renal failure.	
o Radiation sickness.
o GI disorders.
o Cancer chemotherapy
 – high doses.	
o Schizoprenia 
o Parkinson’s disease treatments 
– block the large DA transmission induced by the Parkinson’s drugs ONLY in the CTZ and not where the treatments are working on.
37
Q

describe the pharmacokinetics of D2 receptor antagonists like metoclopramide and domperidone?

A

o Administration: Oral (extensive 1st-pass metabolism), IV.
o Metoclopramide crosses the BBB (so CNS side effects).
o both cross the placenta
– care must be taken with the bioavailability of both drugs.
o Absorption/effectiveness of digoxin may be reduced.
o Nutrient supply may be compromised; especially important in diabetes mellitus patients.

38
Q

what are the unwanted side effects of the metoclopramide and domperidone?

A

have CNS effects (as they cross BBB) and have an endocrine effect

CNS effects (mainly metoclopramide):
- Drowsiness
- Dizziness
- Anxiety.		
- Extra-pyramidal reactions (EPS)
– children more susceptible – Parkinson’s-like syndrome.

Endocrine system effects:

  • Hyperprolactinaemia (dopamine inhibits prolactin)
  • Galactorrhoea
  • Disorders of menstruation
39
Q

what are some mechanistic triggers of nausea and vomiting?

A
  • cytotoxic drugs
  • bacterial toxins
  • motion sickness
  • GI problems
  • pregnancy
  • higher function problems
40
Q

what are the main categories of drugs used to treat nausea and vomiting?

A
  • Muscarinic receptor antagonists (motion sickness)
  • Histamine receptor antagonists (motion sickness)
  • D2 receptor antagonists (gastroparesis)
  • 5HT3a receptor antagonists (chemotherapy)
  • cannabinoids
41
Q

summary of main side effects

A

musc –> drowsiness, dry mouth , blurred vision

H1–> drowsiness

D2–> EPS, sedation, fatigue, restlessness

5HT3a–> headaches, GI upsets (uncommon)

42
Q

what are the receptor targets of promethazine?

what are the system targets ?

A 
as its a mixed receptor competitive antagonist:
- histaminergic (H1) MAIN
- cholinergic (muscarinic)
- dopaminergic (D2) 
receptors. 
[H1>mAChR>D2]

Acts centrally

  • vestibular nucleus–> H1
  • CTZ–> Musc, D2
  • vomiting centre (VC)
43
Q

what are the projections from the vestibular system to the vomiting centre?

A

vestibular nuclei projections

also to CTZ

44
Q

what are the projection from the GIT and periphery to the vomiting centre?

A

vagus
glossopharyngeal
splanchnic
SNS ganglia

(vagus and splanchnic only to CTZ)

LCRS Pharma (32 decks)

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