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GI Pharmacology > Drugs Affecting the GIT > Flashcards

Drugs Affecting the GIT Flashcards

1
Q

How do NSAIDS promote peptic ulcer disease?

A
  • irritate gastric mucosa
  • inhibit PG synthesis by blocking COX
    • PGs normally reduce gastric acid, increase mucus and bicarbonate production (cytoprotective of gastric mucosa)
    • blockage promotes ulcer formation, irritates existing ulcers
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2
Q

What causes PUD?

A
  • H. pylori
  • NSAID use
  • smoking
  • caffeine
  • glucocorticoid use
  • alcohol
  • bile
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3
Q

What classes of drugs are used to treat PUD?

A
  • H+/K+ ATPase inhibitors/PPIs
  • H2 receptor antagonists
  • antacids
  • cytoprotective agents
  • spasmolytics (anticholinergics and direct)
  • prostaglandin E analogues
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4
Q

H2 receptor antagonists block which mediators of gastric acid release?

A

histamine (directly)

ACh and gastrin (indirectly, preventing histamine release from ECL cells)

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5
Q

What is the cytoprotective effect of prostaglandins in gastric mucosa?

A

PGE2 and PGI2 stimulate secretion of mucus and bicarbonate, stimulate mucosal blood flow (removes stray H+ ions)

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6
Q

Omeprazole (Losec, Prilosec), Esomeprazole (Nexium)

A

H+/K+ ATPase/Proton Pump Inhibitors (PPI)

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7
Q

How do PPIs work?

A
  • eg Omeprazole, Esomeprazole (greater bioavailability)
  • irreversibly inhibit H+/K+ ATPase pump on lumenal surface of parietal cells
    • decreses gastric acid formation
  • used for ~8 wks
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8
Q

What are PPIs used for?

A
  • PUD (peptic ulcer disease)
  • reflux oesophagitis
  • Zollinger-Ellison syndrome (gastrin-secreting tumour +acidity)
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9
Q

What are the side effects of PPIs?

A
  • excessive inhibition of acid secretion (Rx for ~8wks)
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10
Q

Cimetidine, Ranitidine (Zantac)

A

H2 receptor antagonists

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11
Q

How do H2 receptor antagonists work?

A

Block H2 receptors on basolateral surface of parietal cells

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12
Q

Antacids

A
  • sodium bicarbonate (systemic)
  • magnesium hydroxide/carbonate/oxide/trisilicate (fast acting, cause diarrhoea)
  • aluminium hydroxide (slow acting)
  • calcium carbonate (fast acting)
  • Gaviscon (sodium bicarbonate + calcium carbonate + sodium alginate)
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13
Q

What are the dangers of antacids?

A
  • easily available, self-medication
  • interactions with prescription drugs
  • systemic (sodium bicarbonate) can have adverse effects:
    • bicarbonate causes systemic alkalosis, sodium affects fluid retention (hypertension, renal failure)
  • magnesium salts cause diarrhoea
  • calcium carbonate and aluminium hydroxide cause constipation
  • magnesium can anaesthetise children
  • calcium salts cause rebound acidity requiring progressively increased dose
    • stimulate gastrin release, which increases acid secretion
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14
Q

Hyoscine butylbromide

A

spasmolytic: anticholinergic/muscarinic receptor antagonist

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15
Q

What is the function of hyoscine butylbromide?

A
  • spasmolytic muscarinic receptor antagonist
  • blocks GIT muscarnic receptors from ACh to decrease motility
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16
Q

What is the function of prostaglandin E analogues?

A

increase mucus secretion, bicarbonate secretion, and mucosal blood flow (to clear H+)

decrease gastric acid secretion

Misoprostol

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17
Q

Misoprostol

A

Prostaglandin E analogue

cytoprotective agent

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18
Q

What are the side effects of prostaglandin E analogues?

A
  • increased utierine motility (used in abortions)
  • increased bowel motility
    • causes severe colic, diarrhoea
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19
Q

What is commonly prescribed with long-term NSAID use?

A

PPIs, prostaglandin E analogues

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20
Q

PPIs are used in treatment of

A

PUD and GORD

(peptic ulcer disease and gastro-oesophageal reflux disease)

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21
Q

The vomiting centre is located

A

in the dorsolateral reticular formation in the floor of the 4th ventricle of the medulla oblongata

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22
Q

Where is the chemoreceptor trigger zone located?

A

in the medulla, outside the blood-brain barrier

23
Q

The CTZ responds to

A

circulating toxins, cytotoxic drugs, chemotherapeutic agents,

24
Q

The vomiting centre receives input from

A

CTZ, vestibular apparatus (ear), higher brainstem and cortical centres,

visceral afferents from the heart, testes, GIT, etc.

25
Q

Vomiting that involves stimulation of the CTZ is caused by

A

stimulation of D2 (dopamine) and 5HT3 (serotonin) receptors

from circulating substances in the blood

26
Q

What receptors are involved in motion sickness?

A

muscarinic and H1

27
Q

Motion sickness, or vomiting due to labyrnthitis, dizziness, or vertigo, is treated with what classes of drugs?

A

muscarinic M1 receptor antagonists

histamine H1 receptor antagonists (older, sedative versions)

28
Q

Hyoscine hydrobromide

A
  • muscarinic receptor antagonist
  • anti-emetic for motion sickness
  • can cross BBB
  • sedative but less so than in Travacalm, a combination with dimenhydrinate (H1 receptor antagonist)
29
Q

H1 receptor antagonists

A
  • anti-emetic drugs:
    • dimenhydinate
    • promethazine
    • pheniramine
30
Q

Promethazine (Phenergan)

A
  • H1 receptor antagonist anti-emetic
  • one of the earliest discovered (previously used to settle babies, motion sickness)
    • extremely sedative​
  • cannot be given to children under 6
31
Q

What are the side effects of drugs used to treat motion sickness?

A

highly sedative

32
Q

What classes of drugs are used to treat vomiting induced by the CTZ?

A

dopamine D2 receptor antagonists and serotonin 5HT3 receptor antagonists

33
Q

dopamine D2 receptor antagonists

A
  • metoclopramide (Maxalon)
  • phrochlorperazine (Stematil)
  • domperidone (peripheral)
  • chlorpromazine (anti-psychotic)
  • haloperidol (anti-psychotic)
  • droperidol (anti-psychotic)
34
Q

Metoclopramide (Maxalon)

A
  • dopamine D2 receptor antagonist anti-emetic
    • increases ACh stim to gut (dopamine inhibits ACh)
  • used for vomiting and nausea induced by CTZ
  • has pro-motility effects (eg in gastric stasis)
    • tf enhances absorption of drugs
  • weak 5HT3 receptor antagonist (high doses)
  • 5HT4 agonist - increases ACh stim of upper GIT (+motility)
35
Q

Prochlorperazine (Stematil)

A

dopamine D2 recceptor antagonist anti-emetic

used for nausea and vomiting induced by the CTZ

36
Q

Domperidone

A

dopamine D2 receptor antagonist anti-emetic

used for nausea and vomiting induced by CTZ

peripheral - although similar to metoclopramide, does not cross BBB tf less potent

37
Q

What are the side effects of dopamine D2 receptor antagonists that act in the CNS?

A
  • extrapyramidal:
    • effects of Parkinson’s disease and other motor disorders
    • tardive dyskinesia (can be irreversible)
    • dystonias
    • changes in facial movements
    • muscular problems
  • occur with prolonged use (especially metoclopramoide)
38
Q

What are the side effects of muscarinic antagonists?

A

anti-SLUD

  • anti: salivation, lacrimation, urination, defacation
  • dry mouth, blurred vision, urinary retention, constipation
39
Q

What are the side effects of seratonin 5HT3 receptor antagonists?

A

anti-emetic drugs

  • headache
  • constipation
40
Q

Ondansetron

A
  • seratonin 5HT3-R antagoist anti emetic
  • widely used in hospitals
41
Q

How do cytotoxic drugs trigger vomiting in the gut?

A
  • release of 5HT (seratonin) from enterochromaffin cells stimulated by the drugs
  • 5HT binds 5HT3 receptor that sends a message to CTZ to trigger vomiting
42
Q

Aprepitant

A

neurokinin-1 R antatonist anti-emetic

used in combination with D2R antagonists and 5HT3R antagonists

43
Q

Dexomethasone

A

glucocorticoid steroid

used in combo with other drugs for N & V

44
Q

emetic drugs

A
  • morphine, opioids, apo-morphine (D2R agonist)
  • induce vomiting
    • toxins
    • aversion therapy
  • reflex emetics via 5HT3 stimulation in the gut
    • ipecacuanha (ipecac makes you yak!)
45
Q

bulking agents

A

laxatives:

  • bran
  • psyllium
46
Q

How do bulking agent laxatives work?

A

ingestable fibre that absorbs water to increase intestinal contents and stimulate normal reflex bowel activity

47
Q

Docusate

A
  • faecal softener/lubricant detergent laxative
  • enhances mixture of water into faeces
  • popular in combination with stimulant laxatives (eg with senna in Coloxyl)
48
Q

Magnesium sulphate (Epsom salts)

A
  • saline osmotic laxative
    • causes osmotic fluid retention to increase fluid volume and stimulate defecation
49
Q

stimulant laxatives

A
  • bisacodyl, senna
  • may stimulate myenteric plexuses, irritate intestinal mucosa or nerve endings to increase motility and reduce reabsorption of water and electrolytes
50
Q

bisacodyl

A

stimulant laxative

51
Q

senna

A

stimulant laxative

most commonly in combination with docusate (coloxyl)

52
Q

Loperamide

A

opioid antidiarrhoeal

(does not cross BBB)

53
Q

Simethicone

A
  • defoaming polymer (coalesces gas bubles) anti-flatulent
  • often combined with loperamide (anti-diarrhoeal)
  • not absorbed by gut
  • changes surface tension of air bubbles so that they combine

GI Pharmacology (1 decks)

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