Drugs To Treat Disorders Of Gastric Acid Secretion

Question 1

Describe factors pro (3) and anti (2) acid secretion

Answer 1

pro:
ACh, gastrin, histamine

anti:
somatostatin, prostaglandins

Question 2

4 classes of drug used to treat disorder of acid secretion

Answer 2

alginates and antacids
drugs that protect the mucosa
H2 receptor antagonists
PPIs

Question 3

how do antacids work, give an example

Answer 3

act by buffering gastric acid, raising the gastric pH

calcium carbonate and magnesium carbonate (Rennies)

Question 4

how do alginates work, give an example

Answer 4

anionic polysaccharides that form a viscous gel on contact with water, protecting the oesophageal mucosa fom reflux. floats on surface of stomach contents reducing acid reflux symptoms

e.g. sodium alginate, sodium bicarbonate and calcium carbonate (Gaviscon)

Question 5

How does trisodium dicitratobismuthate work. 5 actions. name 2 side effects

Answer 5

coats the mucosa
adsorbs pepsin
increases PG synthesis
stimulates HCO3- secretion
mild antibiotic

nausea/vomiting and reversible blackening of tongue and faeces.

Question 6

how do H2 receptor antagonists work. give an example.

Answer 6

block the action of histamine on parietal cells = decreased acid secretion.

e.g. Ranitidine (Zantac))

Question 7

How do proton pump inhibitors work. give an example

Answer 7

activated by acid in the stomach lumen. inhibition of the H+/K+ ATPase = decreased acid secretion.

e.g. lansoprazole/omeprazole.

Question 8

name 2 indications for acid secretion drug treatment

Answer 8

reflux oesophagitis

peptic ulcer

Question 9

what is reflux oesophagitis

Answer 9

inflammation of the lower oesophagus produced by repeated episodes of gastric reflux

Question 10

symptoms and complications of reflux oesophagitis

Answer 10

symptoms:
heartburn
regurgitation
haematemesis

complications:
oesophageal ulceration
peptic stricture (narrowing)
barrett’s oesophagus

Question 11

what is barretts oesophagus

Answer 11

replacement of the stratified squamous epithelium of the lower oesophagus with simple columnar epithelium and goblet cells. Type of metaplasia. It is a precancerous lesion.

Question 12

3 things that cause peptic ulcers

Answer 12

NSAIDs
Zollinger-Ellison Syndrome
H. pylori infection

Question 13

preventing NSAID-related GI effects (5 options)

Answer 13

alternative drug
lowest dose/shortest duration
avoid concomitant NSAIDs e.g. aspirin for heart failure
frequent review of need for NSAIDs
coprescribe PPI

Question 14

What is Zollinger-Ellison Syndrome. Treatment?

Answer 14

Endocrinopathy - increased levels of gastrin produced e.g. a gastrin producing tumour. Gastrin acts to increase acid secretion but also causes parietal cell hyperplasia. Greatly increased acid production.

PPIs. Surgery if caused by a tumour.

Question 15

how is h.pylori implicated in ulcer formation

Answer 15

causes breaks in the mucosal barrier. secretes urease which breaks down urea into NH3 and CO2. NH3, acid and pepsin damage epithelial cell layer.

Question 16

what is achlorhydria/hypochlorhydria, how can it be caused, what are the potential consequences

Answer 16

absence/deficiency of HCl acid in gastric juice

iatrogenic (over reduction of acid secretion e.g. PPIs), atrophy of gastric mucosa (e.g. elderly).

reduced ability to digest nutrients, increased vulnerability to bacterial infection.

Question 17

Describe mechanism of acid secretion (4 steps)

Answer 17

carbonic anhydrase CO2 + H20 –> H+ + HCO3-
H+ pumped into stomach lumen by H+/K+ ATPase
HCO3- moves out of basolateral membrane via Cl- antiported
Cl- diffuses out of luminal side into stomach via Cl- channel.