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PA2131 Pharmacology > Drugs Used for Gastritis and Peptic Ulcer > Flashcards

Drugs Used for Gastritis and Peptic Ulcer Flashcards

1
Q

List THREE classes of agents that reduce gastric acidity.

A

Antacids

H2‐receptor Antihistamines

Proton Pump Inhibitors (PPI)

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2
Q

List THREE examples of mucosal protective agents

A

Sucralfate

Misoprostol

Bismuth Compounds

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3
Q

Rank common antacids according to their rate of neutralization.

A

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

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4
Q

Why is simethicone often found in antacid formulations?

A

Antifoaming activity coalesces bubbles and reduces bloating.

Helps to reduce gastric distention, belching discomfort side effects.

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5
Q

Why are magnesium and aluminium compounds usually formulated together in antacids?

A

Magnesium causes osmotic diarrhoea

Aluminum causes constipation

Together the effects balance

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6
Q

List adverse effects of antacids.

A
  • Sodium compounds: Fluid retention, hypertension, caution in heart failure
  • Sodium bicarbonate: may cause sodium overload, alkalosis on long term usage
  • Calcium compounds: Hypercalcaemia, rebound acid secretion, renal stones (calcium phosphate precipitate)
  • Carbonates and bicarbonates: CO2 gas formation resulting in gastric distention, belching
  • Magnesium compounds: Osmotic diarrhoea
  • Aluminium compounds: Constipation
  • Avoid long-term use in patients with renal insufficiency
  • Affect absorption of other medications
    • Do not take within 2 hours of other medication
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7
Q

Name an example of an H2 antihistamine

A

Cimetidine, ranitidine, famotidine

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8
Q

When is the best time to take H2 antihistamines?

A

Effective in controlling fasting and nocturnal acid release. As many patients with peptic ulcers have elevated nocturnal acid release, usually taken on an empty stomach before sleep at night.

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9
Q

List adverse effects of H2 antihistamines.

A

Common: constipation, headaches

Uncommon: agitation

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10
Q

List adverse effects of cimetidine.

A
  • Mental confusion in elderly, critically ill patients, or renal/hepatic dysfunction
  • Anti-androgenic: inhibits estradiol metabolism, increases serum prolactin
    • Men: gynaecomastia, impotence
    • Women: galactorrhoea
  • Inhibits CYP450 (2D6, 1A2) increasing plasma
    • Prolongs half-life of other drugs e.g., anti-depressants, warfarin, theophylline, paracetamol, caffeine
    • Similar interactions not significant with other H2 antihistamines e.g., ranitidine, famotidine
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11
Q

Name ONE example of a proton-pump inhibitor

A

Omeprazole, esomeprazole, and other *prazole

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12
Q

Briefly describe the mechanisms of action of PPIs that result in selective proton pump inhibition in the parietal cell canaliculi

A
  • Inactive pro-drugs (absorbed well)
  • Enteric-coated formulation (protect from gastric acid)
  • 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
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13
Q

Briefly describe the duration of action of omeprazole.

A
  • Plasma T½ 1h but effective for 18-24 h due to irreversible inhibition of proton pumps
  • 3-4 days before full inhibition of all proton pumps.
  • 4-5 days after drug withdrawal to return to pre-treatment acid level due to time required to synthesize new proton pump
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14
Q

When is the best time to take PPIs?

A
  • Inhibits active pumps, not quiescent pumps
    • Best to be present during mealtimes
  • Short serum T1/2 = 1-2hr; Tmax = 2-4hr
    • Given 1hr before meal
  • Bioavailability decreased 50% by food
    • ​Given on empty stomach (usually before breakfast)
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15
Q

List adverse effects of omeprazole.

A
  • Nausea, diarrhoea, colic, headache, dizziness
  • Reduced gastric acid barrier –bacterial overgrowth
  • Skin rashes,
  • Transient increase in hepatic aminotransferase occasionally
  • Inhibition of metabolizing enzyme CYP450 2C19
    • increasing diazepam concentrations
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16
Q

Briefly describe the properties and mechanisms of action 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
17
Q

Briefly describe the clinical use and adverse effects of sucralfate

A
  • Adminstered on empty stomach (at least 1hr before meals)
  • Limited use for ulcers today as PPIs are more effective
    • Still used for prevention of stress-related bleeding in critically ill patients
  • Adverse effects:
    • Few as insoluble and not systemically absorbed
    • Constipation
    • Impairs absorption of other drugs e.g., theophylline, digoxin
18
Q

Briefly describe the mechanisms of action of bismuth compounds as mucosal protective agents.

A

Mechanisms of action:

  • Bismuth forms a protective layer protecting ulcers from acid and pepsin
  • Stimulates mucus and bicarbonate secretion
  • Directly anti-microbial activity against H. pylori
19
Q

Briefly describe the 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
  • 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
  • But bismuth compounds generally have a good safety profile when used short-term for ulcers
  • Harmless blackening of stool and reversible darkening of tongue
20
Q

Why is use of misoprostol limited?

A

Limited use today due to:

  • Adverse effects
  • Multiple daily dosing (non-compliance)
  • Advent of COX-2 selective NSAIDs
  • Potential for abuse as an abortifacient
21
Q

List adverse effects of misoprostol.

A

Adverse Effects:

  • Abdominal pain/cramps
  • Diarrhoea
  • Abortion (uterine contraction)
  • Bone pain and hyperostosis (excessive bone growth)
22
Q

Explain the properties and mechanisms of action of misoprostol

A
  • Synthetic PGE1 analogue
  • Rapidly absorbed after oral dosing
  • Short T1/2 = 30 min; must be given 3-4 times per day
  • Indications
    • Prevention of NSAID-induced peptic ulcers
  • Mechanisms of action:
    • Binds to PGE2 receptors (EP1-4)
    • Low dose (cytoprotective): promotes bicarbonate and mucus secretion, enhances mucosal blood flow
    • High dose (antisecretory): inhibits gastric acid secretion
23
Q

What is triple therapy?

A

Two antibiotics + 1 PPI (7-14 days)

  • Antisecretory Agent e.g., Omeprazole OR Esomeprazole
  • Antibiotics: Clarithromycin PLUS Amoxicillin OR Metronidazole (in patients allergic to penicillins)
24
Q

What is the role of PPI in triple therapy?

A
  • Mechanisms of PPI in triple therapy:
    • Direct antimicrobial properties (minor)
    • Raises intra-gastric pH (pH3.5 – 5.5) lowering minimum inhibitory concentration (MIC) of the antibiotics against H. pylori
  • After completion of triple therapy, the PPI is continued for 4-6 weeks to ensure complete healing
25
Q

What is quadruple therapy?

A

Second-line “quadruple therapy” (useful in areas of high prevalence of resistance to clarithromycin or metronidazole)

  • 1 Bismuth + 2 antibiotics (metronidazole+tetracycline) + 1 PPI (10-14 days)
26
Q

List adverse effects of triple therapy

A

Common side effects are diarrhoea, nausea and vomiting

PA2131 Pharmacology (14 decks)

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