Drugs Affecting the GIT

Question 1

List 5 ways in which drugs can affect the GI tract.

Answer 1

1 - Anti ulcer drugs.

2 - Drugs affecting GI tract motility.

3 - Drugs used in inflammatory bowel disease.

4 - Emetics and antiemetic drugs.

5 - Drugs affecting bile synthesis.

Question 2

What is gastric acid composed of?

Answer 2

Pepsin and hydrochloric acid.

Question 3

Why, when treating an ulcer, is dealing with the acid more important than dealing with the pepsin?

Answer 3

Because pepsin doesn’t function at pH > ~5.

Question 4

List 3 behavioural changes that might help to treat ulcers.

Answer 4

1 - Lose weight.

2 - Reduce spicy food / alcohol intake.

3 - Chew food more thoroughly.

Question 5

List 4 methods, other than behavioural methods, that can be used to treat ulceration / damage caused by gastric acid.

Answer 5

1 - Antacids.

2 - Inhibit acid secretion.

3 - Enhance protection of gastric mucosa.

4 - Antibacterial drugs (e.g. some ulcers caused by Helicobacter pylori).

Question 6

What are antacids and what are they used for?

Answer 6

• Weak bases.

- Can be used to treat dyspepsia, ulcers and gastric cancers.

Question 7

What is acid rebound?

Which drugs might cause this?

Answer 7

• An increase in acid secretion when pH increases.

- Antacids cause this as they neutralise gastric acid.

Question 8

List 3 examples of antacids.

Answer 8

1 - Sodium bicarbonate.

2 - Magnesium hydroxide.

3 - Calcium carbonate.

Question 9

List 4 characteristics of sodium bicarbonate when used as an antacid.

Answer 9

1 - Instant effects (highly soluble).

2 - Wears off quickly.

3 - Releases CO2.

4 - Absorbed by the GIT.

Question 10

What are the implications of CO2 release from antacids?

Answer 10

• Cause belching.

- Stretching of the stomach is a trigger for acid secretion.

Question 11

Why might taking too much sodium bicarbonate or calcium hydroxide cause alkalosis?

Answer 11

Both antacids are absorbed by the GIT (inc. Ca2+ and Na+ in the lumen).

Question 12

List 2 characteristics of magnesium hydroxide when used as an antacid.

Answer 12

1 - Longer activity (less soluble).

2 - Not absorbed by the GIT.

Question 13

Why might taking too much magnesium hydroxide cause osmotic diarrhoea?

Answer 13

It is not absorbed by the GIT, so remains in the lumen of the intestine.

Question 14

Why might calcium carbonate lead to acid rebound (other than due to decreasing acidity)?

Answer 14

Increased Ca2+ is a trigger for acid secretion.

Question 15

What is milk alkali syndrome and how might it be caused?

Answer 15

• A mixture of alkalosis and high blood calcium.

- Can be caused by excessive calcium carbonate intake.

Question 16

List 3 ways in which antacids might be commercially prepared.

Answer 16

1 - Antacids combined with each other.

2 - Antacids combined with alginates.

3 - Antacids combined with dimethicone.

Question 17

What is the purpose of combining antacids with alginates?

Give an example of a commercial drug that uses alginates.

Answer 17

The alginate forms a gel to enhance mucosal protection (e.g. Gaviscon).

Question 18

What is the purpose of combining antacids with dimethicone?

Answer 18

Dimethicone prevents foaming, relieving trapped air.

Question 19

Why are antacids alone not used to cure ulcers?

What is the preferred treatment?

Answer 19

• High doses are required to be taken frequently, so there are strong side effects.
• It is better to target the acid secretion.

Question 20

Which cells secrete gastric acid?

Answer 20

Oxyntic cells (AKA parietal cells)

Question 21

Which molecule is responsible for gastric acid production?

Answer 21

The H+/K+ ATPase.