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Clinical Pharmacology, Therapeutics & Intro to Prescribing > Lecture 19 – GI Pharmacology > Flashcards

Lecture 19 – GI Pharmacology Flashcards

1
Q

peptic ulceration involves

A

gastric and uodenal ulcers

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2
Q

symptoms of peptic ulcerations are not

A

a reliable guide to ulcer location e.g. epigastric pain

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3
Q

chronic ulcers cna be

A

asymptomatic

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4
Q

adverse events of peptic ulceration

A
  • Bleeding, perforation, scarring and possible obstruction
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5
Q

acid and peptic ulceration

A
  • Acid essential for ulceration and inability of normal [acid] to inhibit further acid is a significant factor
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6
Q

risk factors of peptic ulcers

A
  • Early gastric emptying also risk factor
  • Helicobacter pylori is a major risk factor
  • NSAIDs most common cause after H. pylori

Smoking and alcohol delay healing

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7
Q

How is acid produced by parietal cells

A
  • Apical membrane has H+/K ATPase pump, K+ and Cl- pumps
  • On the basal membranes HCO3-/Cl- antiport
  1. Carbonic anhydrase produces H2CO3 from water and carbon dioxide
  2. This dissociates to form HCO3- and H+
  3. H+ is pumped out of the cell on the apical membrane in exchange for potassium which comes into the cell
  4. Potassium conc of the lumen is replenished by the K+ transporter
  5. The chloride channel allows Cl- to move out of the cell into the lumen and combine with H+ à HCL
  6. Meanwhile the Cl- conc of the cell is maintained by the HCO3-/Cl- antiport on the basal membrane
  7. Influx of HCO3- into bloodstream= ALKALINE TIDE
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8
Q

drugs used to treat peptic ulceration

A
  • Alginates and antacids
  • PPIs
  • H2 receptor antagonists
  • aminosalicylates
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9
Q

name a drug undee the class Alginates and antacids

A

gaviscon

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10
Q

gaviscon is a compound of

A
  • Alginic acid (sodium alginate) +
  • Antacid (aluminium hydroxide/magnesium carbonate)
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11
Q

alginates and antacids (gaviscon) Uses

A

Protect the oesophageal mucosa from acid reflux

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12
Q

Mode of action of gaviscon

A
  • Antacids- buffer stomach acid
  • Alginic acid (seaweeds)- increase stomach content viscosity and reduce reflux
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13
Q

Adverse drug response of gaviscon

A
  • Magnesium salts can cause diarrhoea
  • Aluminium salts can cause constipation
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14
Q

Contraindication gaviscon

A
  • Na+ and K+ containing preparations should be used with caution in renal failure
  • High [sucrose] in some preparations- hyperglycaemia in DM
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15
Q

Drug-drug interactions gaviscon

A
  • Can reduce absorption of many drugs so doses should be separated
  • Increased urine alkalinity can increase aspirin excretion
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16
Q

name 2 proton pump inhibitors

A
  • Lansoprazole
  • Omeprazole
17
Q

uses of PPis

A

Uses (often prescribed alongside long term NSAID or steroid)

  • Relive acid reflux symptoms and GERD
  • Duodenal or stomach ulcers
  • Treat damage to lower oesophagus caused by acid reflux
18
Q

Mode of action of PPis

A
  • Irreversibly inhibit the H+/K+ ATPase in gastric parietal cells
  • Final stage in pathway therefore very significant reduction in acid secretion
19
Q

Adverse drug response PPIs

A
  • GI disturbances- abdominal pain, constipation, diarrhoea
  • Headache, dizziness
  • Drowsiness/confusion
20
Q

Contraindication PPIs

A
  • BEWARE: can mask symptoms of gastro-oesophageal cancer
  • Osteoporosis – fracture risk
21
Q

Drug-drug interactions

A
  • Omeprazole is CYP inhibitor- reduced clopidogrel action
  • PPIs can increase effects of warfarin and phenytoin- need to monitor
  • Should be given shortest effective duration at lowest effective dose
22
Q

name a h2 receptor antagonist

A

ranitidine

23
Q

Uses of ranitidine (H2 receptor antagonist)

A
  • Indigestion
  • Heart burn
  • Acid reflux
  • Protect the oesophageal mucosa from acid reflux
24
Q

Mode of action raniditine

A
  • Local histamine release contributes to proton pump activation
  • H2 receptor antagonists inhibit H2 receptors reducing this local histamine release –> therefore only partial reducing in acid secretion
25
Q

Adverse drug response ranitidine

A

Generally well tolerated- diarrhoea, headache

26
Q

Drug-drug interactions ranitidine

A

Few DDIS

27
Q

cureent large scale recall of most ranitidine due to

A

possible carcinogenic contaiminantion

  • iansoprazole typically first alternative upon pt review
28
Q

Helicobacter pylori and peptic ulceration

A
  • major risk fact
  • gram negative bacteria
  • infection: H. pyrlori infects lower part of the stomach antrum
  • inflammation: inflammation of gastric mucosa (gastritis)- often asymptomatic
  • ulcer: gastric inflammation may lead to duodenal or gastric ulcer

- complications: bleeding ulcer and perforated ulcer

29
Q

% of people in UK infected

A

10-15% (infection from childhood)

30
Q

consider H. pylori for all pts with

A
  • duodenal or gastric ulcers not associated with NSAID or unresponsive to lifestyle PPI and antacids
31
Q

confirmation of H.pylori infection

A
  • Urea breath test
    • Gastric urea= C12 isotopes (99%) and C13 isotopes= 1%
    • Pts ingest urea with enriched C13
    • H. pyrloi should convert this to ammonia and CO2
    • Can detect C13 in exhaled CO2
  • Stool antigen test
  • Endoscopy with biopsy
32
Q

treatment of H pylori

A
  • One week triple therapy
  • PPI + two antibacterial agents
    • Lansoprazole + clarithromycin + amoxicillin OR
    • Lansoprazole + clarithromycin + metronidazole (where allergic to amoxicillin )
      • Some evidence of local metronidazole resistance
  • Compliance with full course important for effectiveness and minimise risk of bacterial resistance
33
Q

name a drug under the class aminosalicylates

A

mesalazine (enteric coated tablet)

34
Q

mesalazine uses

A

first line treatment in UC

35
Q

Mode of action mesalazine

A
  • Release of 5-aminosalsylic acid
  • Topical anti-inflammatory action at the colon (enteric coated tablets limit gastric breakdown)
  • Mesalazine has no role in rheumatoid arthritis (no systemic effect)
    • Sulfasalazine has more side effects so used infrequently for UC but sulfa group good for rheumatoid arthritis
36
Q

Adverse drug response mesalazine

A
  • GI disturbance- nausea, dyspepsia
  • Leukopenia- rare
37
Q

Contraindication mesalazine

A

Salicylates like aspirin- similar hypersensitivity

38
Q

Drug-drug interactions mesalazine

A

Enteric coated tablets may break down quicker in presence of PPI (because of increase pH)

Clinical Pharmacology, Therapeutics & Intro to Prescribing (39 decks)

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