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Block 1 > Drugs To Treat Disorders Of Acid Secretion > Flashcards

Drugs To Treat Disorders Of Acid Secretion Flashcards

1
Q

What are the main 3 classes of drugs used to treat disorders of acid secretion?

A
  1. Antacids + alginates
  2. Histamine H2-receptor antagonists (old gold standard)
  3. Proton pump inhibitors (new gold standard)
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2
Q

What is an antacid?

A

Any substance, generally a base, which counteracts stomach acidity by buffering gastric acid thereby, raising the gastric pH

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3
Q

What are some examples of antacids?

A

Aluminium hydroxide + magnesium hydroxide (Maalox)

Calcium carbonate + magnesium carbonate (Rennie)

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4
Q

What is an alginate?

A

Anionic polysaccharide that forms a viscous gel upon binding water so they increase viscosity of stomach contents forming a ‘raft’ that floats on the surface of stomach contents protecting the oesophageal mucosa from acid reflux + reducing symptoms of reflux

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5
Q

How are alginates often taken?

A

In combination with antacids for use in reflux oesophagitis

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6
Q

What are some examples of alginates?

A

Sodium alginate
Sodium bicarbonate
Calcium carbonate (Gaviscon combines all 3)

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7
Q

What do histamine-H2 receptor antagonists do?

A

Competitively inhibit histamine action at H2 receptor on parietal cells by binding the receptor, blocking it + preventing histamine from binding to stimulate acid secretion inhibiting acid secretion by about 90%

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8
Q

What is one benefit of taking histamine H2-receptor antagonists?

A

The drugs are specific as the H2 receptor is not really expressed anywhere other than parietal cells

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9
Q

What are some examples of histamine H2-receptor antagonists?

A

Cimetidine (Tagamet)

Ranitidine (Zantac)

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10
Q

What is one downside to taking Cimetidine?

A

It inhibits many cytochrome P450 enzymes weakly so has a few side effects as a result

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11
Q

What are some examples of proton pump inhibitors (PPIs)?

A

Omeprazole (Losec, Prilosec + Zegerid)

Lansoprazole (Prevacid, Zoton + Inhibitol)

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12
Q

Why are proton pump inhibitors (PPIs) better at treating acid secretion disorders than histamine H2-receptor antagonists?

A

Histamine H2-receptor antagonists only block the proportion of acid secretion stimulated by histamine whereas PPIs are uniquely targeting the actual proton pump which stops H+ secretion irreversibly

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13
Q

What do proton pump inhibitors (PPIs) do?

A
  1. From the circulation, the lipophilic pro-drug traverses the parietal cell + enters the canaliculus
  2. Become trapped + accumulate in the secretory canaliculi of parietal cells
  3. Activated in acid environment (inactive at neutral pH) - very specific in being directed to the site of action
  4. Binds + IRREVERSIBLY inhibits the H+/K+ ATPase pump - the terminal step in the acid secretory pathway
  5. For acid secretion to resume, new pump molecules must be synthesized via protein synthesis (2-3 days)
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14
Q

How is omeprazole administered? Why?

A

In capsules containing enteric-coated granules because it degrades rapidly at low pH

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15
Q

What is the half-life (T1/2) of proton pump inhibitors (PPIs)?

A

1 hour

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16
Q

Increases doses of proton pump inhibitors (PPIs) give ______ __ __ in plasma concentration.

A

Disproportionately higher increases

17
Q

What conditions require drug treatment of acid secretion?

A

Reflux oesophagitis

Peptic ulcer from NSAIDs or H. Pylori infection

18
Q

What is reflux oesophagitis?

A

Inflammation of the lower oesophagus produced by persistent episodes of reflux (GORD) where the liquid content of the stomach regurgitates into the oesophagus

19
Q

What are symptoms of reflux oesophagitis?

A

Heartburn

Regurgitation of food into mouth

Haematemesis (vomiting blood as a result of ulceration)

20
Q

What are the complications of reflux oesophagitis?

A

Oesophageal ulceration

Peptic stricture

Barrett’s oesophagus (in a small proportion of patients)

21
Q

How is reflux oesophagitis often treated?

A
  1. Antacids + alginates: OTC so self-medicated before consultation or prescribed in mild cases
  2. H2- receptor antagonists: available OTC used to self-medicate if antacids/alginates fail
  3. PPIs: prescribed drugs of choice for all but mild cases
22
Q

What causes a peptic ulcer?

A

Persistent irritation/gastritis

23
Q

What types of peptic ulceration exist?

A

Benign

Deep

24
Q

Where do more peptic ulcers arise than in the stomach?

A

Duodenum

25
Q

What do prostaglandins E2 and I2 do?

A

Stimulate gastric mucus + HCO3- production

Inhibit gastric acid production

26
Q

What are some examples of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)?

A

Ibuprofen

Aspirin

Naproxen

27
Q

Why would a patient have to be on Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) long-term?

A

Long-term pain or inflammation management

28
Q

What do Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) do?

A

Inhibit COX, which is the enzyme that converts arachidonic acid to PGs I2 + E2 so they inhibit PG formation thereby impairing the renewal of the gastric mucosal barrier impairing gastroprotection -> gastric erosions causing or worsening ulcers

29
Q

When trying to avoid the adverse effects of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), what should be considered?

A

Alternative drug? E.G. Ibuprofen is lower risk than Naproxen

Lowest dose + shortest duration

Avoid concomitant NSAIDs

Frequent review of need for NSAIDs

Co-prescription of PPI in patients at increased risk of adverse effects + requiring NSAIDs

30
Q

What is Helicobacter Pylori (H. Pylori)?

A

A spiral-shaped gram -ve bacterium ingested by mouth, which damages stomach + duodenal tissue

31
Q

How does Helicobacter Pylori (H. Pylori) damage the gut?

A

Penetrates gastric mucus barrier/cells facilitating acid + protease penetration

Produces + secretes urease which breaks down urea into CO2 + NH3 (ammonia):

  • NH3 neutralises gastric acid
  • NH3, other bacterial products + acid damage epithelial cells
32
Q

What percentage of peptic ulcers are causes by Helicobacter Pylori (H. Pylori)?

A

80%

33
Q

What is the treatment of Helicobacter Pylori (H. Pylori)?

A

Eradication regime involves a combination of antibiotics + a PPI -> produces long-term remission of peptic ulcers

34
Q

What is achlorhydria/hypochlorhydria?

A

Absence/deficiency of HCl in gastric juice

35
Q

What are some causes of under-secretion of gastric acid?

A

Iatrogenic (caused by drugs)

Atrophy of gastric mucosa in older adults

36
Q

What are the consequences of under-secretion of gastric acid?

A

Impaired ability to digest + absorb certain nutrients such as iron + the B vitamins

Increased vulnerability of GI tract to bacterial infection

Block 1 (54 decks)

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