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pipi&pi2 > Antiemetics > Flashcards

Antiemetics Flashcards

1
Q

What is the difference acute and delayed N&V?

A
  • Acute: <24 hours
  • Delayed: >24, usually 2-5 days after trigger
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2
Q

What are the 7 major targets for treatment of N&V?

A

Low emetic risk + acute:
- Serotonin/5-HT3 antagonists
- Corticosteroids
- Dopamine receptor antagonists

High emetic risk + acute:
- “3x
- Neurokinin receptor antagonists

High emetic risk + delayed:
- (Corticosteroids, dopamine, NK1)
- (Mixed dopamine) + muscarinic receptor antagonists

Anticipatory:
- Benzodiazepines

Motion sickness:
- (Mixed muscarinic) + H1 histamine receptor antagonists

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3
Q

What is the PP of N&V?

A
  • Vomiting caused by noxious (stimulus strong enough to cause tissue damage) stimulation on 1 of 4 sites which trigger the vomiting centre

1) CTZ
- Lacks BBB so it can detect noxious chemicals in the blood

2) GIT
- Has mechanoreceptors to detect distention eg
- Has chemoreceptors to detect poisons eg

3) Vestibular system
- Detects motion
- Sensitive to some opioids used as analgesics (increase risk of MS)

4) High systems of the CNS
- Pain, mood sensitivity to stimuli

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4
Q

What is the difference between the vomiting centre and chemoreceptor trigger zone?

A
  • Vomiting center: Motor aspects of vomiting (contraction of abdominal muscles, relaxation of the lower esophageal sphincter, and activation of the diaphragm)
  • CTZ: Detecting chemical stimuli in the blood and cerebrospinal fluid. Detects various substances such as toxins, drugs, and metabolic disturbances.
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5
Q

What drugs are used for low emetic risk but acute N&V?

A

1) Serotonin 5-HT3 Antagonists
- Odansetron
- (Granisetron, Palonosetron)

2) Corticosteroids
- Dexamethasone
- (Methylprednisolone)

3) Dopamine D2 Receptor Antagonists
- Metoclopramide
- Olanzepine

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6
Q

What is the MOA of 5-HT3 receptor antagonists?

A
  • Only affect 5-HT3 receptors in the GIT
  • Drug blocks transmission of signals of distension and stimuli from visceral part of GIT to CNS
  • Enhanced efficacy if + Corticosteroid and NK1 RA
  • IV 30 min before/ orally 1 hr before chemo (prevent acute chemo-induced vomiting)
  • Also useful for small-bowel obstruction
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7
Q

What are the major adverse effects in 5-HT3 RA?

A
  • Headache, dizziness, drowsiness, constipation/diarrhea
  • Caution when taking drugs that are extensively metabolised by CYPP450 enymes
  • Small risk of cardiac arrhythmia
    ~ Prolonged QT interval
  • Small risk of orofacial malformations in babies whose mother was on odansetron
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8
Q

What is the MOA of corticosteroids?

A
  • Mimic effects of endogenous cortisol
  • Better efficacy when used together with 5-HT3 RA when treating acute/delayed nausea and px w high emetogenic chemo therapies
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9
Q

What are the major concerns when taking corticosteroids?

A
  • Rare with short-term use
  • Higher doses/long-term use (>2 weeks) may cause iatrogenic Cushing’s syndrome
    ~ Weight gain
    ~ Impaired wound healing/easy bruising
    ~ Osteoporosis
    ~ Immunosuppression
    ~ Hyperglycaemia
    ~ Hypertension, bradycardia
    ~ Dyspepsia (indigestion)
    ~ GERD
    ~ Mood swings
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10
Q

What is the MOA for Dopamine D2 RA?

A
  • Antagonist effects at the CTZ
  • Prokinetics to stimulate GI motility
    ~ Only useful if bowel is not completely obstructed (^ in pressure may cause bowel rupture)
  • Used for milder N&V but as an adjunct for more severe forms
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11
Q

What are the major concerns for D2 RA?

A
  • Extrapyramidal symptoms (EPS) (involved in voluntary movements)
    ~ Parkinsonian symptoms (rigidity, tremors, bradykinesia, restlessness)
    ~ Must only be used short-term (tardive dyskinesia may develop irreversibly)
  • Galactorrea, menstrual disorders, gynaecomastia, impotence from elevated prolactin
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12
Q

What drugs are used to treat high emetic risk but acute N&V?

A
  • 5-HT3 RA
  • Corticosteroids
  • D2 RA

+
- Neurokinin NK1 RA
~ Aprepitant
~ (Fosaprepitant)

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13
Q

What’s the MOA of NK1 RA?

A
  • Block action at NK1 receptors in CTZ
  • Used together with 5-HT3 RA and corticosteroids to prevent acute and delayed nausea caused by highly emetogenic chemo
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14
Q

What are the major concerns of NK1 RA?

A
  • Fatigue, hiccups, diarrhoea/constipation
  • Peripheral neuropathy, imbalance in blood cells
  • Metabolism by CYP3A4
    ~ Risk of interaction with other chemotherapeutic agents
    ~ Drugs that ihibit CYP3A4 may influence plasma levels
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15
Q

What drugs can be used to treat high emetic risk + delayed N&V?

A
  • Mixed D2 + muscarinic RA + antihistamines (Antipsychotics)
    ~ Prochlorperazine
    ~ Promethazine
    ~ Olanzapine
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16
Q

How do antipsychotics work in treating N&V?

A
  • D2 RA @ CTZ
  • Muscarinic antagonism @ vestibular system and vomiting center
  • Antihistamine @ vestibular system and vomiting center
17
Q

What drugs are used to treat anticipatory N&V?

A
  • Benzodiazepines
    ~ Lorazepam
    ~ (Diazepam)
18
Q

What is the MOA of benzodiazepines?

A
  • Binds to allosteric site (where regulation occurs) which increases chloride conductance
    ~ ^ Inhibition in the brain and dampens overactivity
  • Anxiolytic
19
Q

What are the major concerns of taking benzodiazepines?

A
  • Sedative / hypnotic
  • Additive effects with other sedative drugs can lead to respiratory depression on overdose
  • Effects on fetus during 1st trimester of pregnancy (risk of cleft palate)
20
Q

What drugs can be used to prevent motion sickness?

A
  • Muscarinic receptor antagonist
    ~ Hyoscine
  • Antihistamine
    ~ Cinnarizine
21
Q

What is the MOA for muscarinic RA in preventing motion sickness?

A
  • Acts on vestibular system and vomiting center
  • Antispasmodic for abdominal cramps by reducing GI motility
22
Q

What are the major concerns for anticholinergic/muscarinic RA drugs?

A
  • Anticholinergic adverse effects
    ~ Dry mouth, blurry vision
    ~ Sedation, confusion
23
Q

What is the MOA for H1 antihistamine RA?

A
  • H1 histamine receptor antihistamine
  • M1 cholinergic receptor antagonism.
  • Sedative effects of diphenhydramine may be useful in treating emesis caused by chemo
24
Q

What are the major concerns for H1 antihistamine RA?

A
  • Sedative (more pronounced)
  • Dry mouth, blur vision, constipation
25
Q

What is the pharmacotherapy for pregnant women?

A
  • Implement dietary changes first
  • Pyridoxine (vitamin B6) supplements
  • May + with doxylamine if vit b6 is insufficient
    ~ Antihistamine with muscarinic antagonism
26
Q

What is the pharmacotherapy for children?

A
  • Prokinetic agents (eg metoclopramide)
    ~ For gastroparesis (stomach paralysis)
  • 5-HT3 RA
    ~ For postoperative or chemotherapy-induced N&V

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