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pharm - OBG > Anti-Emetics > Flashcards

Anti-Emetics Flashcards

1
Q

State the 5 major classes of anti-emetic drugs.

A

Mixed receptor antagonists

Dopamine (D2) receptor antagonists

Muscarinic receptor antagonists

Serotonin (5-HT3) receptor antagonists

Cannabinoids

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2
Q

What is nausea and vomiting often preceded by?

A

Sweating, salivation and an increase in heart rate

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3
Q

Describe the process of vomiting.

A

Stomach, oesophagus and associated sphincters are relaxed

Contraction of upper small intestine, pyloric sphincter and pyloric region of stomach

Contents of upper jejunum, duodenum and pyloric region of stomach move to the body and fundus of the stomach

Lower and upper oesophageal sphincters and oesophagus relaxes

glottis closes, abdominal contractions to increase abdominal pressure to force stomach contents out

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4
Q

What are the consequences of severe vomiting?

A

Dehydration

Hypochloraemic metabolic alkalosis

Contributes to reduction in bicarbonate excretion and increase in bicarbonate reabsorption

Increase in sodium reabsorption and increase in potassium excretion (hypokalaemia)

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5
Q

What types of receptors in the stomach transmit signals to the vomiting centre and chemoreceptor trigger zone?

A

Chemoreceptors and Mechanoreceptors

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6
Q

What is special about the location of the CTZ and vomiting centre?

A

It is located in a part of the brain that has a very porous blood brain barrier

So the CTZ and vomiting centre act as an early warning system to protect the brain from toxin damage

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7
Q

Give an example of a mixed receptor antagonist.

A

Promethazine

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8
Q

Describe the mode of action of this drug. (Promethazine-mixed receptor antagonist)

A

It is a competitive antagonist for the following receptors:
-Histaminergic
-Muscarinic
-Dopaminergic

Order of potency of antagonist activity: H > M > D

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9
Q

What are the uses of promethazine?(mixed receptor antagonist)

A

Motion sickness

Disorders of the labyrinth

Hyperemesis gravidarium

Pre and post-operatively

Relief of allergic symptoms, anaphylactic emergency, night sedation; insomnia

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10
Q

Describe the pharmacokinetics of promethazine-mixed receptor antagonist

A

Administer orally

Onset of action – 1-2 hours

Peak action – 4 hours

Duration of action – 24 hours

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11
Q

What are the unwanted effects of promethazine?

A

Dizziness

Tinnitus

Fatigue

Sedation

Convulsions

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12
Q

Give 2 examples of dopamine receptor antagonists.

A

Metoclopramide

Domperidone

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13
Q

Describe the order of agonist potency of these drugs.

A

D > H > M

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14
Q

What effect do these drugs (dopamine receptor antagonists. ) have on the GI tract?

A

They have PROKINETIC effects on the GI tract:
 Increase smooth muscle motility
 Accelerate gastric emptying
 Accelerate the transit time of intestinal contents

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15
Q

Why are these drugs (dopamine receptor antagonists) poor at treating motion sickness?

A

The vestibular system has connections to the CTZ and it has direct connections to the vomiting centre

The dopamine antagonists block dopamine receptors in the CTZ but they are not blocking the rest of the signals that are going directly from the vestibular system to the vomiting centre

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16
Q

State some uses of metoclopramide and domperidone.

A

Uraemia (severe renal failure)

Radiation sickness

GI disorders

Cancer chemotherapy

17
Q

Which of these drugs (dopamine receptor antagonists) crosses the BBB?

A

Metoclopramide

18
Q

Why must care be given over the bioavailability of co-administered drugs when patients are on dopamine receptor antagonists?

A

These drugs have prokinetic effects on the GI tract hence they accelerate the transit through the GI tract – this may mean that some drugs are not sufficiently absorbed in the GI tract e.g. digoxin

19
Q

What are some unwanted effects of metoclopramide and domperidone? (dopamine receptor antagonists)

A

CNS side effects only with metoclopramide:
 Drowsiness
 Dizziness
 Anxiety
 Extrapyramidal reactions (Parkinsonian like syndrome – children more susceptible)

Endocrine side effects:
 Hyperprolactinaemia
 Galactorrhoea
 Disorders of menstruation

20
Q

Give an example of a muscarinic receptor antagonist.

A

Hyoscine

21
Q

What is the mode of action of muscarinic receptor antagonists?

A

Act centrally on the CTZ, vestibular nuclei and vomiting centre to block the activation of the vomiting centre

22
Q

What is hyoscine used for? (muscarinic receptor antagonist)

A

Prevention of MOTION SICKNESS

Sometimes used in operative pre-medication

23
Q

Describe the pharmacokinetics of hyoscine. (muscarinic receptor antagonist)

A

Administered orally (peak effect 1-2 hours)

Could also be administered via a transdermal skin patch

24
Q

What are the unwanted effects of hyoscine? (muscarinic receptor antagonist)

A

Drowsiness

Dry mouth

Cycloplegia

Mydriasis

Constipation

25
Q

Give an example of a serotonin receptor antagonist.

A

Ondansetron

26
Q

What is the mode of action of serotonin receptor antagonists?

A

Act to block transmission in visceral afferents and CTZ

27
Q

What is the main use of serotonin receptor antagonists as an anti-emetic?

A

MAIN USE: preventing anti-cancer drug induced vomiting (especially cisplatin)

Also used for radiotherapy induced sickness and post-operative nausea and vomiting

28
Q

Describe the pharmacokinetics of ondansetron? (serotonin receptor antagonists)

A

Adminsitered orally

Excreted in urine (good kidney function required)

29
Q

What are the unwanted effects of ondansetron?

serotonin receptor antagonist

A

Headache

Sensation of flushing and warmth

Constipation-increased large bowel transit time

30
Q

Explain the use of combined ondansetron (serotonin receptor antagonists) therapy with glucocorticoids.

A

Corticosteroids can be used in combination with ondansetron to treat moderate to high emetogenic chemotherapy

The improved efficacy of the combined treatment may be due to the anti-inflammatory properties of corticosteroids

31
Q

how do cannabinoids reduce nausea

A

reduce levels of NTs associated with vomiting and nausea

pharm - OBG (25 decks)

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