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262B Pharmacology > L20 - GI Drugs > Flashcards

L20 - GI Drugs Flashcards

1
Q

What is the function of the GI tract?

A
  • ingestion
  • motility
  • secretion
  • digestion
  • absorption
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2
Q

What is the neurological control of the GI tract?

A
  • CNS

- enteric NS

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3
Q

What are the hormones that play a role in the GIT?

A
  • acetylcholine (ACh)
    acts through muscarinic receptors to induce motility and secretion
  • serotonin (5HT)
    released in response to stress and food and triggers gastric motility (peristalsis)
  • dopamine
    produced by muscle and epithelial cells + inhibits neurotransmitter release to decrease motility
  • histamine
    acts through H1 receptors in brain (induces nausea) or H2 receptors in gut (induces gastric acid secretion)
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4
Q

What cells are involved in gastric acid secretion?

A
  • parietal cells produce HCl

- chief cells produce pepsinogen which is converted to pepsin (protease)

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5
Q

What are the protective mucosal factors in the stomach?

A
  • prostaglandins (COX1)
  • mucus
  • bicarbonate
  • mucosal blood flow
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6
Q

What are the aggressive factors in the stomach that promote disease?

A
  • acid
  • pepsin
  • NSAIDs
  • helibacter pylori
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7
Q

What are gastric disorders characterised by? What disorders can this lead to?

A

characterised either by:

  • hypersecretion of gastric acid
  • lack of mucous secretion

common disorders:

  • gastroesophageal reflux disorder (GORD)
  • peptic ulcers
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8
Q

What is GORD? What is it caused by?

A
  • gastroesophageal reflux disorder

- caused by reflux of gastric acid into the oesophagus = heartburn

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9
Q

If unresolved, what can GORD develop into?

A
  • erosive inflammation in the oesophagus

- adenocarcinoma (cancer which forms in mucous-secreting glands)

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10
Q

What are the treatment options for GORD?

A

increase gastric pH

  • antacids
  • H2 (histamine) receptor antagonist
  • proton pump inhibitor (ulcers) (preferred for mild-severe gastric-acid related diseases)

protect gastric mucosa
- coating agents

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11
Q

What are antacids and their mechanism of action?

A
  • weak bases (CaCO3, Mg(OH)2, Al2(OH)3)
  • neutralise acid to form water and salt
  • thus raises gastric pH
    DOES NOT PREVENT OVERPRODUCTION OF ACID
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12
Q

When are antacids used?

A

used for mild cases of GORD

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13
Q

What are the adverse effects of antacids?

A
  • excessive use can result in kidney stones with calcium salts

adverse effects rare and depend on the salt used:

  • Al + Ca = constipation
  • Mg = diarrhoea
  • CaCO3 = produces gas and belching
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14
Q

What are H2 (histamine) antagonists? What is their mechanism of action?
HISTAMINE ANTAGONISTS IMPORTANT

A
  • H2 receptors are GsPCR
    the receptors increase cAMP and PKA which activates proton pump (H+/K+ ATPase) = increases gastric acid secretion
    the receptor modulates histamine, gastrin and ACh induced acid secretion via pre-synpatic receptors
  • histamine antagonists are competitive antagonists that prevent the receptor activation
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15
Q

What is are the 4 histamine antagonists?

HISTAMINE ANTAGONISTS IMPORTANT

A
  • cimetidine (bold)

- ranitidine, famotidine, nizatidine

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16
Q

When are histamine H2 antagonists used?

HISTAMINE ANTAGONISTS IMPORTANT

A

use in the treatment of mild peptic ulcers and mild GORD

- not directly affecting acid production

17
Q

What are the adverse effects of histamine H2 antagonists?

HISTAMINE ANTAGONISTS IMPORTANT

A

usually rare and minor side effects

  • dizziness
  • headache
  • diarrhoea
  • muscular pain

abrupt withdrawal can result in transient increase in gastric acid secretion due to upregulation of H2 receptors as compensation for receptor activity inhibition
= relapse of peptic ulcer or GORD

18
Q

Where can peptic ulcers occur?

A
  • stomach
  • duodenum
  • lower oesophagus
19
Q

What are the risk factors of peptic ulcers?

A 
Helicobacter pylori is a major causative factor
also include:
- smoking
- excessive alcohol
- genetic factors
- NSAID use
- physical and emotional stress
they somehow turn down the protective mechanism in the stomach lining
20
Q

What are the symptoms of peptic ulcers?

A
  • abdominal pain made worse by food (time to pain depends on location of ulcer)
  • nausea/vomiting
  • loss of appetite and weight loss
  • blood in faeces due to bleeding
21
Q

Why does Helicobacter pylori cause peptic ulcers?

A
  • eats away at mucosal layer
  • expose endothelial cells to acid = ulcer

diagnosed by endoscopic biopsy

22
Q

What are the treatment options for peptic ulcers due to H. pylori?

A

first-line treatment
- broad spectrum antibiotics (amoxycillin)

other:
- proton pump inhibitor (omeprazole)
for treatment of symptoms - increase pH by inhibiting gastric acid secretion

23
Q

What is the mechanism of action for proton pump inhibitors? How are they different to histamine antagonists?

A
  • bind to gastric proton pump (H+/K+ ATPase) and inactivates

- cf. histamine antagonists: more potent because both basal and stimulated acid secretion is inhibited

24
Q

What are the benefits of proton pump inhibitors?

A
  • rapidly absorbed from the small intestine
  • short plasma half-life ~2 hours
  • have prolonged duration of effect due to covalent binding to H+/K+ ATPase pump = convenient once daily dosing
    once PPIs bind to pump it stays for the life of the cell ~2-3 days
25
Q

What are the adverse effects and interaction associated with proton pump inhibitors?

A 
they are generally well tolerated but more likely to have side effects than with histamine antagonists
minor adverse effects:
- headache
- abdominal pain
- nausea

interactions:

  • PPIs metabolised before excretion so caution needed for patients with hepatic disease because less effective
  • Oemprazole inhibits CYP2C19 = decreases metabolism of other drugs associated with that enzyme
  • interacts with absorption of drugs that require acidic environment of stomach (e.g. aspirin)

262B Pharmacology (18 decks)

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