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systemic pharmaco > GIT - Anti-emetics - Drugs used in nausea & vomiting > Flashcards

GIT - Anti-emetics - Drugs used in nausea & vomiting Flashcards

1
Q

Sites that trigger the vomiting centre

A
  1. Chemoreceptor Trigger Zone
    - in the area postrema of the floor of the 4th ventricle
    - stimulated by blood borne toxins
    - D2, NK-1 & 5-HT3 receptors
  2. GIT & heart, visceral afferents
    - stimuli from pharynx & stomach (mechanoreceptors, chemoreceptors, CN IX/X afferents, release of serotonin from gut enterochromaffin cells)
    - 5-HT3 receptors on vagal afferents
  3. Vestibular System
    - motion sickness/disease eg labyrinthitis
    - H1 & ACh M1 receptors on vestibular afferents
  4. Higher Centres in the CNS
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2
Q

Classes of anti-emetics & examples

A
  1. Serotonin 5-HT3 Antagonist (Ondansetron)
  2. Corticosteroids (Dexamethasone, methylprednisolone)
  3. Neurokinin Receptor Antagonist (substance P antagonist) (Aprepitant - oral, Fosaprepitant - IV)
  4. Dopamine Receptor Antagonist (Metoclopramide)
  5. Muscarinic Receptor Antagonist (Hyoscine - scopolamine)
  6. H1 Histamine Receptor Antagonist (H1 + M1 - Diphenhydramine, D2 + H1/M1 - promethazine, droperidol)
  7. Benzodiazepines (Lorazepam, Diazepam)
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3
Q

Mechanism of action of ondansetron

A

Acts on 5-HT3 receptors primarily in the GIT

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4
Q

Uses of ondansetron

A
  1. Acute chemotherapy-induced vomiting (IV/orally 30min/1h before)
    - generally not effective for delayed nausea & vomiting (>24h after chemo)
    - enhanced by corticosteroids & NK1 receptor antagonists
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5
Q

Toxicity of ondansetron (2)

A

Generally well tolerated

  1. Headache, dizziness, constipation
  2. Cardiac arrhythmia (prolongation of QT interval) - small risk
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6
Q

Mechanism of action of corticosteroids

A

Mimics effects of cortisol, basis for anti-emetic effect unknown

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7
Q

Uses of corticosteroids

A
  1. Acute & delayed nausea & vomiting
    - with moderately to highly emetogenic chemo regimens
    - often used with 5-HT3 antag
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8
Q

Toxicity of corticosteroids

A

Unlikely with short term use

  1. Iatrogenic Cushing’s Syndrome
    - redistribution of fat (rounded face), muscular wasting, dysphonia, thinning of skin, easy bruising, hyperglycemia, later diabetes, osteoporosis, immunosuppression
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9
Q

Mechanism of aprepitant

A

Acts on Neurokinin-1 receptors in area postrema (CTZ)

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10
Q

Uses of aprepitant

A
  1. Acute & delayed nausea & vomiting (due to highly emetogenic chemotherapy)
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11
Q

Toxicity of aprepitant (4)

A
  1. Fatigue
  2. Dizziness
  3. Diarrhea
  4. Interacts with chemotherapeutic agents (docetaxel, etoposide, irinotecan, imatinib, vinblastine) & may be influenced by CYP3A4 inhibitors (ketoconazole, clarithromycin, ritonavir, verapamil)
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12
Q

Mechanism of action of metoclopramide

A

Dopamine (especially D2) receptor antagonist, acts on CTZ

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13
Q

Uses of metoclopramide (2)

A
  1. Anti-emetic

2. Prokinetic to stimulate GI motility

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14
Q

Toxicity of metoclopramide (3)

A
  1. Extrapyramidal side effects - restlessness, dystonias, parkinsonian symptoms - esp elderly
  2. Irreversible tardive dyskinesia (involuntary repetitive motor movements) - long term
  3. Elevated prolactin levels - galactorrhea, gynecomastia, impotence, menstrual disorders
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15
Q

Mechanism of action of hyoscine

A

Muscarinic receptor antagonist (anti-cholinergic) - action in estibular system and vomiting centre

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16
Q

Uses of hyoscine

A
  1. Motion sickness
17
Q

Toxicity of hyoscine

A

Increases when given orally - transdermal patch

1. Anticholinergic (parasympatholytic) adverse effects - dry mouth, blurring of vision, constipation, reduced secretions

18
Q

Mechanism of diphenhydramine

A

M1 cholinergic receptor antagonism + H1 histamine receptor antagonism - acts on vomiting centre & vestibular system

19
Q

Uses of diphenhydramine (2)

A
  1. Motion sickness

2. Emesis due to chemotherapy (sedative effects)

20
Q

Toxicity of diphenhydramine (2)

A
  1. Sedation (H1 receptors antagonism)

2. Anticholinergic (dry mouth, constipation, vision blurring)

21
Q

Mechanism of action of mixed D2, M1/H1 receptor antagonists (anti-psychotics)

A

Dopamine receptor antagonism - CTZ

M1/H1 receptor antagonism - vomiting centre, vestibular system

22
Q

Toxicity of mixed D2, M1/H1 receptor antagonists (4)

A
  1. Sedative
  2. Extrapyrimidal side effects
  3. Hypotension
  4. Droperidol - prolognation of QT interval - risk of cardiac arrhythmias
23
Q

Mechanism of action of benzodiazepines

A

Binds to allosteric site on GABA receptors - increase chloride conductance

24
Q

Uses of benzodiazepines

A
  1. Anxiolytic - reduces anticipatory vomiting/vomiting caused by anxiety
25
Q

Toxicity of benzodiazepines + Contraindications (2+1)

A
  1. Sedative/hypnotic
  2. Additive effects with other sedative drugs/depressants - respiratory depression on overdose
  3. Pregnancy (esp 1st trimester) - teratogenic, risk of cleft palate

systemic pharmaco (18 decks)

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