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F. Gastrointestinal Drugs > 1. Drugs used in Gastritis & Peptic Ulcer Disease > Flashcards

1. Drugs used in Gastritis & Peptic Ulcer Disease Flashcards

1
Q

Types of drugs used in gastritis & peptic ulcer diseases

A
  1. Agents that reduce gastric acidity:
    - antacids
    - H2-receptor antagonists
    - proton pump inhibitors
  2. Mucosal protective agents
    - sucralfate
    - misoprostol
    - bismuth compounds
  3. Triple-therapy for H. Pylori eradication
    - clarithromycin
    - amoxicillin/metronidazole
    - omeprazole
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2
Q

Examples of antacids

A

NaHCO3, CaCO3, Mg(OH)2, Al(OH)3

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3
Q

Rate of neutralisation of antacids

A

NaHCO3 > CaCO3 > Mg(OH)2 > Al(OH)3

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4
Q

Why do some antacids contain simethicone?

A

Simethicone is a anti-forming agent → eases release of gas within the GI tract via burping or flatulence

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5
Q

Adverse effects of antacids

A
  1. Na+ → Fluid retention, hypertension, CHF
  2. Ca2+ → Hypercalcaemia, rebound acid secretion
  3. HCO3-, CO3- → CO2 gas formation resulting in gastric distention, belching
  4. Mg2+ → osmotic diarrhoea
  5. Al3+ → constipation
  6. Avoid long-term use in patients with renal insufficiency
  7. Affect absorption of other medications → do not take within 2 hours of other medication
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6
Q

Why is Mg2+ and Al3+ combined together in antacids

A

Mg2+ → osmotic diarrhoea
Al3+ → constipation
Combined formulation minimises impact on bowel function

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7
Q

Examples of H2-receptor antagonist

A
  1. Cimetidine
  2. Ranitidine
  3. Famotidine
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8
Q

MOA of H2-receptor antagonist

A
  1. Competitive inhibitors of H2 receptors on parietal cells

2. Suppress gastric acid secretion and pepsin concentration induced by histamine, gastrin and acetylcholine

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9
Q

Efficacy of H2-receptor antagonist

A
  1. Inhibits 60-70% of total 24-hr gastric acid secretion
  2. Very effective at inhibiting nocturnal acid secretion (due to histamine)
  3. Modest effect on meal-induced acid secretion (due to gastrin and acetylcholine)
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10
Q

Adverse effects of cimetidine

A
  1. Mental confusion in critically ill patients or in renal/hepatic dysfunction
  2. Anti-androgenic, inhibits estradiol metabolism, increases serum prolactin
    • Men: gynaecomastia, impotence
    • Women: galactorrhoea
  3. Inhibits cytochrome P450
    • Prolongs half-life of other drugs e.g. warfarin, theophylline
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11
Q

Examples of proton-pump inhibitors

A
  1. Omeprazole

2. Esomeprazole

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12
Q

MOA of proton-pump inhibitor

A
  • Inactive pro-drugs (absorbed well)
  • Enteric-coated formulation (protects activation before absorption)
  • Released and absorbed in intestines
  • Protonated, activated and concentrated in parietal cell canaliculi
  • Reactive thiophilic sulphenamide active drug (not absorbed well)
  • Forms covalent disulphide bonds with H+-K+-ATPase (irreversible)
  • Inhibits gastric acid secretion

Some anti-microbial activity against H. Pylori

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13
Q

Pharmacokinetics of PPIs

A
  1. Bioavailability decreased 50% by food → Given on empty stomach (usually before breakfast)
  2. Inactivate active pumps not quiescent pumps → Must be present during meal time
  3. Short serum T1/2 = 1-2hr; Tmax = 2-4hr – Given 1hr before meal
  4. Duration of action 24hr as irreversibly blocks proton pumps → Once daily is sufficient
  5. Takes 3-4 days to fully inhibit acid secretion
  6. Efficacy:
    – Mean 24hr intra-gastric pH increases to pH 3-4
    – Mean number of hours of pH > 4 ranges from 10-14hr
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14
Q

Adverse effects of PPIs

A
  • Can cause headaches, nausea, constipation, flatulence, diarrhoea
  • Ca deficiency, risk of osteoporosis, bone fracture: hip, wrist and spine [chronic high dose]
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15
Q

MOA of sucralfate

A

• Salt of sucrose complexes to sulphated Al(OH)3
• Highly insoluble therefore no systemic effects
• Breaks down to sucrose sulphate (strong negative charge) + aluminium salt
• Mechanism of action:
– Negatively charged sucrose sulphate binds positively charged proteins at ulcer crater forming a viscous, tenacious gel that prevents further acid attack
– Stimulates mucosal prostaglandin and bicarbonate secretion

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16
Q

Uses of sucralfate

A
  • Limited use for ulcers today as H2 antagonists and PPIs are more effective
  • Still used for prevention of stress-related bleeding in critically ill patients
17
Q

Adverse effects of sucralfate

A
  1. Constipation

2. Impairs absorption of other drugs

18
Q

How should sucralfate be administered

A

on empty stomach (at least 1hr before meals)

19
Q

Examples of bismuth compounds

A
  1. Bismuth subsalicylate for dyspepsia and acute diarrhoea

2. Bismuth subcitrate potassium for “quadruple therapy” eradication of H. pylori

20
Q

MOA of bismuth compounds

A
  1. Bismuth forms a protective layer protecting ulcers from acid and pepsin
  2. Stimulates mucus and bicarbonate secretion
  3. Directly anti-microbial activity against H. pylori
21
Q

Adverse effects of bismuth compounds

A

• Although > 99% of bismuth is eliminated in stool <1% is absorbed and stored in many tissues, elimination is by slow renal excretion
• But bismuth compounds generally have a good safety profile when used short-term for ulcers
• Harmless blackening of stool and reversible darkening of tongue
• Prolonged use may rarely produce bismuth toxicity resulting in encephalopathy (ataxia, headaches, confusion, seizures)
– Use only for short periods
– Avoid in patients with renal insufficiency

22
Q

Indications for misoprostol

A

Prevention of NSAID-induced peptic ulcers

23
Q

MOA of misoprostol

A
  1. Binds to PGE2 receptors (EP1-4)
  2. Low dose (cytoprotective): promotes bicarbonate and mucus secretion, enhances mucosal blood flow
  3. High dose (antisecretory): inhibits gastric acid secretion
24
Q

Adverse effects of misoprostol

A
  1. Abdominal pain
  2. Diarrhoea
  3. Abortion (uterine contraction)
  4. Bone pain and hyperostosis (excessive bone growth)
25
Q

Why is misoprostol usage limited today?

A
  1. Adverse effects
  2. Multiple daily dosing (non-compliance)
  3. Advent of COX-2 selective NSAIDs
  4. Potential for abuse as an abortifacient
26
Q

Triple therapy for eradication of H. Pylori

A

Omeprazole/esomeprazole + Clarithromycin + Amoxicillin/Metronidazole

For 7-14 days

27
Q

Mechanism of PPI in triple therapy

A
  1. Direct antimicrobial properties (minor)
  2. Raises intra-gastric pH (pH3.5 – 5.5) lowering minimum inhibitory concentration (MIC) of the antibiotics against H. pylori

After completion of triple therapy → PPI is continued for 4-6 weeks to ensure complete healing

28
Q

Quadruple therapy for the eradication of H. Pylori

A

1 Bismuth + 2 antibiotics + 1 PPI or H2 antagonist (10-14 days)

29
Q

Common side effects of triple / quadruple therapy

A

Diarrhoea, nausea and vomiting

F. Gastrointestinal Drugs (3 decks)

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