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Drugs Affecting the GIT Flashcards

(53 cards)

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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?

Study These Flashcards
A

in the medulla, outside the blood-brain barrier

23
Q

The CTZ responds to

Study These Flashcards
A

circulating toxins, cytotoxic drugs, chemotherapeutic agents,

24
Q

The vomiting centre receives input from

Study These Flashcards
A

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

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

25
Vomiting that involves stimulation of the CTZ is caused by
stimulation of D2 (dopamine) and 5HT3 (serotonin) receptors from circulating substances in the blood
26
What receptors are involved in motion sickness?
muscarinic and H1
27
Motion sickness, or vomiting due to labyrnthitis, dizziness, or vertigo, is treated with what classes of drugs?
muscarinic M1 receptor antagonists histamine H1 receptor antagonists (older, sedative versions)
28
Hyoscine _hydrobromide_
* 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
H1 receptor antagonists
* anti-emetic drugs: * dimenhydinate * **promethazine** * pheniramine
30
Promethazine (Phenergan)
* 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
What are the side effects of drugs used to treat motion sickness?
highly sedative
32
What classes of drugs are used to treat vomiting induced by the CTZ?
dopamine D2 receptor antagonists and serotonin 5HT3 receptor antagonists
33
dopamine D2 receptor antagonists
* **metoclopramide (Maxalon)** * **phrochlorperazine (Stematil)** * domperidone (peripheral) * chlorpromazine (anti-psychotic) * haloperidol (anti-psychotic) * droperidol (anti-psychotic)
34
Metoclopramide (Maxalon)
* 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
Prochlorperazine (Stematil)
dopamine D2 recceptor antagonist anti-emetic used for nausea and vomiting induced by the CTZ
36
Domperidone
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
What are the side effects of dopamine D2 receptor antagonists that act in the CNS?
* 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
What are the side effects of muscarinic antagonists?
anti-SLUD * anti: salivation, lacrimation, urination, defacation * **dry mouth, blurred vision, urinary retention, constipation**
39
What are the side effects of seratonin 5HT3 receptor antagonists?
anti-emetic drugs * headache * constipation
40
Ondansetron
* seratonin 5HT3-R antagoist anti emetic * widely used in hospitals
41
How do cytotoxic drugs trigger vomiting in the gut?
* 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
Aprepitant
neurokinin-1 R antatonist anti-emetic used in combination with D2R antagonists and 5HT3R antagonists
43
Dexomethasone
glucocorticoid steroid used in combo with other drugs for N & V
44
emetic drugs
* 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
bulking agents
laxatives: * bran * psyllium
46
How do bulking agent laxatives work?
ingestable fibre that absorbs water to increase intestinal contents and stimulate normal reflex bowel activity
47
Docusate
* faecal softener/lubricant detergent laxative * enhances mixture of water into faeces * popular in combination with stimulant laxatives (eg with senna in Coloxyl)
48
Magnesium sulphate (Epsom salts)
* saline osmotic laxative * causes osmotic fluid retention to increase fluid volume and stimulate defecation
49
stimulant laxatives
* bisacodyl, senna * may stimulate myenteric plexuses, irritate intestinal mucosa or nerve endings to increase motility and reduce reabsorption of water and electrolytes
50
bisacodyl
stimulant laxative
51
senna
stimulant laxative most commonly in combination with docusate (coloxyl)
52
Loperamide
opioid antidiarrhoeal | (does not cross BBB)
53
Simethicone
* 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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