GI Disorders 1: Vomiting Flashcards Preview

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Flashcards in GI Disorders 1: Vomiting Deck (19)
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1
Q

Reflex Mechanism of Vomiting

purpose?
which stomach cells are involved?

A
  • defensive response to rid toxic material
  • toxins and poisonous compounds induce release of mediators (Serotonin) from enterochromaffin cells lining GI tract
  • trigger signals in vagal afferent fibers
2
Q

Reflex Mechanism of Vomiting

where is it regulated?

what are some causes of vomiting with drugs?

A
  • regulated centrally via vomiting/emetic center in medulla
  • communication with chemoreceptor trigger zone (CTZ) is important
  • vomiting is an unwanted effect of many drugs
  • chemotherapy (drugs target health cells)
  • opioids
  • general anesthetics
  • post-surgery
3
Q

Reflex Mechanism of Vomiting

Pathways

Pain, repulsive sights, smells, emotional stimuli?
Motion sickness?
Toxins in gut?

A

Pain, repulsive sights, smells, emotional
- higher cortical centers directly relay to vomiting centre

Motion sickness
- vestibular nuclei replays to CTZ to vomiting centre

Toxic chemicals in gut
- enterochromaffin cells secrete seotonin, vagal afferents to CTZ and directly to vomiting center

4
Q

Reflex Mechanism of Vomiting

Vomiting vs nausea

what is peripheral vs central pathway for vomiting? (in chemotherapy)

A
  • share similar mechanisms
  • nausea can be mediated through independent mech
  • easier to pharm manage vomiting than nausea
  • defined differently from person experiencing it, cannot test

Peripheral Pathway

  • acute chemotherapy vomiting involves 5HT/5HT3 receptor signaling (0-24 hrs)
  • enterochromaffin cells release serotonin to vagal afferent

Central Pathway

  • delayed involves SP/NK1 receptor signaling (>24 hrs, substance P
  • signal from vomiting center which release sub P to NK1
5
Q

5-HT3 Receptor Antagonists

Names?
Specific use?

A
-SETRON
Ondansetron
Granisetron
Alosetron (original - removed for vomiting)
Palonosetron
  • prophylaxis and treatment of motion sickness and chemotherapy-induced vomiting
6
Q

5-HT3 Receptor Antagonists

MOA?
site of action?
channel types?

A
  • primary site of action is CTZ but also acts on GI tract
  • 5-HT3 receptors mediate contraction of fundus, corpus, antrum of GI tract
  • 5-HT3 receptors sensitize spinal sensory neurons and induce vagal signaling of nausea
  • 5HT receptors are G-protein coupled, except 5HT3 which is a ligand gated cation channel (Na+, K+ channels)
  • vagal sensory aff neurons project to emetic center in brainstem
  • antagonism also slows intestinal transit and secretions of small bowel
7
Q

5-HT3 Receptor Antagonists

Adverse effects?

A
  • well tolerated
  • headache, GI upset (constipation)
  • Ischemic colitis (alosetron) - severe contraction in GI tract used for IBS in women
8
Q

Dopamine Receptor 2 (D2) Antagonists - Phenothiazines

Antipsychotic phenothiazines (4)

Treatment for nausea and vomiting associated with? (5)

A

Chlorpromazine
Perphenazine
Prochlorperazine
Trifluoperazine

Cancer
Radiation therapy
Cytotoxic drugs
Opioids
Anaesthetics
9
Q

Phenothiazines

type

MOA - site of action?

A
  • primary site of action is D2 receptors in CTZ
    D2 is G-coupled receptor
  • linked to Gi which inhibits adenylate cyclase and reduce cAMP formation and activation of protein kinase A (antagonist reverses this leading to high cAMP and PKA)
10
Q

D2 Antagonists - Phenothiazines

AE? (4)

A
  • sedation (chlorpromazine), blocking dopamine recepotrs, movemnt
  • orthostatic hypotension
  • *extrapyramidal syndrom
  • *dystonias: movements in face involuntary, irreversible usually
  • *tardive dyskinesia
  • *hyperprolactinemia: dopamine naturual antagonist of prolactin secretion galactorrhea

-contrainidcation: severe CNS depression

11
Q

Metoclopramide
type?
Actions?

A

D2 Antagonists -

  • related to phenothiazines
  • also block histamine and musc receptors
  • also has peripheral actions (increased GI motility) as well as on CTZ (GI tract and CTZ)
  • blocks D2 in other CNS areas
12
Q

D2 Antagonists - Metoclopramide

AE? (3)

A
  • movement disorders, fatigue, motor restlessness
  • *spasmodic torticollis: invol. twisting of neck
  • *oculogyric crises: upward eye movements
  • *prolactin release
13
Q

Domperidone
type?
special?
AE?

(separate card)
Haloperiodol, droperidol, levomepromazine - use?

A

D2 receptor ant

  • doesn’t penetrate BBB, less CNS effects
  • more specific for D2 receptors on CTZ
  • *small increased risk for serious cardiac AE, prolong QT interval
  • orally
  • other D2 antagonists against acute chemotherapy incuded vomiting (acts on GI tract)
14
Q

Histamine H1 Receptor Antagonist

Name (3)

A

Cinnarizine
Cyclizine
Promethazine

15
Q

Histamine H1 Receptor Antagonist

what types of nausea and vomiting is it used for?

A
  • G-protein coupled receptors linked to Gq proteins
  • effective for nausea and vomiting due to motion sickness
  • drowsiness
  • not in CTZ, not for chemo induced or substances acting on CTZ directly
  • promethazine for pregnancy morning sickness
16
Q

Aprepitant/Fosaprepitant

receptors?
dosage form?

A
  • ant for sub P receptors (NK1) in CTZ ( also vomiting centre and GI tract)
  • fos is IV prodrug of aprep
  • aprep is oral
17
Q

Nabilone

A
  • synthetic cannabinol

- antagonized via naloxone (opiod receptors?)

18
Q

Dexamethasone

A
  • when others fail
  • high doses can prevent vomiting caused by cytotoxic drugs (MOA unknown)
  • glucocorticoid
19
Q

Muscarinic Receptor Antagonists

name (1)
use (1)
dosage form (2)
AE

A

Hyoscine (scopolamine) is main one

  • prevention and treatment of motion sickness
  • given orally or via transdermal patch
  • adverse effects include dry mouth and blurred vision
  • some drowsiness, not as much as antihistamine