Drugs Affecting the Gastrointestinal System

Question 1

What are some causes of peptic ulcers?

Answer 1

H. pylori, NSAIds, smoking, caffeine, alcohol, glucocorticosteroids, bile

Question 2

Why are prostaglandin E2 and I2 protective against ulcers?

Answer 2

The stimulate secretion of mucus and bicarbonate and increase mucosal blood flow to remove stray H+ ions

Question 3

What is the action of H2 receptor antagonists?

Answer 3

Block effects of gastrin, acetylcholine and histamine on parietal cells

Question 4

How do parietal cells secrete acid?

Answer 4

With a proton pump which exchanges H+ for K+ with an ATPase

Question 5

What is omeprazole?

Answer 5

A proton pump inhibitor

Question 6

What is esomeprazole?

Answer 6

A proton pump inhibitor

Question 7

What is ranitidine?

Answer 7

An H2 receptor antagonist

Question 8

What is magnesium hydroxide?

Answer 8

An antacid - used to neutralise stomach acid

Question 9

What is a contraindication of antacids?

Answer 9

Kidney problems

Question 10

What are some side effects of antacids?

Answer 10

diarrhoea and constipation

Question 11

Why do antacids cause rebound acidity?

Answer 11

Because they stimulate gastrin release

Question 12

What are cytoprotective agents?

Answer 12

They coat the ulcer site to protect it from the acid

Question 13

What is hyoscine butylbromide?

Answer 13

a muscarinic receptor antagonist - to reduce motility

Question 14

What is mebeverine?

Answer 14

a non specific muscle relaxant

Question 15

What is misoprostol?

Answer 15

A synthethetic prostaglandin E analogue - to increase mucus secretion and mucosal blood flow and decrease acid secretion

Question 16

What the contraindication of misoprostol?

Answer 16

Pregnancy - will induce motility in uterus and cause an abortion

Question 17

What are other side effects of misoprostol?

Answer 17

colic and diarrhoea

Question 18

What are two inputs to the vomiting centre?

Answer 18

the chemoreceptor trigger zone and the vestibular apparatus

Question 19

What are the receptors for the chemoreceptor trigger zone to the vomiting centre?

Answer 19

D2 receptors and 5HT3 receptors

Question 20

What are the receptors for the vestibular apparatus to the vomiting centre?

Answer 20

H1 receptors and muscarinic receptors

Question 21

What is hyoscine hydrobromide?

Answer 21

a muscarinic receptor antagonist that crosses the blood blood brain barrier for motion sickness

Question 22

What are the side effects of hyoscine hydrobromide?

Answer 22

anti SLUD - dry mouth, dry eyes, urinary retention, constipation

Question 23

What is promethazine?

Answer 23

An H1 receptor antagonist for motion sickness (phenergen)

Question 24

What is metoclopramide?

Answer 24

A D2 receptor antagonist for vomiting and nausea associated with the chemoreceptor trigger zone - also a weak 5HT3 antagonist and a potent 5HT4 agonist - facilitates gastric emptying via increased ACh (but not diarrhoea)

Question 25

What is the effect of facilitating gastric emptying in metoclopramide?

Answer 25

changes the absorption of other drugs

Question 26

What is prochlorperazine?

Answer 26

A D2 receptor antagonist for vomiting and nausea associated with the chemoreceptor trigger zone

Question 27

What are the side effects of D2 receptor antagonists?

Answer 27

extra pyramidal side effects - motor movements like parkinsons and sometimes irreversible tardive dyskinesia

Question 28

What is ondansetron?

Answer 28

A 5HT3 receptor antagonist - used for vomiting and nausea associated with the chemoreceptor trigger zone - blocks both receptors on the the chemoreceptor trigger zone and on vagal afferents which receive signals from the enterochrommaffin cells

Question 29

What are the side effects of 5HT3 receptor antagonists?

Answer 29

very few - minor headache and constipation

Question 30

What is aprepitant?

Answer 30

An NK1 receptor antagonist - a substance P antagonist - substance P is found in high concentrations in the vomiting centre in the brain

Question 31

What is dexamethasone?

Answer 31

A glucocoritcosteroid used to treat nausea and vomiting although not technically an antiemetic

Question 32

What is rabione?

Answer 32

A synthetic cannabinoid - used as an antiemetic

Question 33

What is apomorphine?

Answer 33

A dopa receptor agonist - a very potent emetic

Question 34

What causes constipation?

Answer 34

certain drugs e.g. opioids, lifestyle factors, inadequate dietary fibre intake, inappropriate bowel habits, inadequate activity, spinal injury, dementia, depression, hypothyroidism

Question 35

Apart from constipation, when else are laxatives used?

Answer 35

Before a colonoscopy, hernias, prolapsed rectum

Question 36

What are bulking agents?

Answer 36

indigestible vegetable fibre taken with water to stimulate normal reflex bowel movements

Question 37

What is docusate?

Answer 37

A faecal softener - acts as an emulsifying agent

Question 38

What is liquid paraffin?

Answer 38

A faecal lubricant - may cause loss of fat soluble vitamins

Question 39

What is magnesium sulphate?

Answer 39

an osmotic laxative - causes osmotic fluid retention to get more mass and more distension

Question 40

What is bisacodyl?

Answer 40

A stimulant laxative - precise mode of action not known but causes increased motility

Question 41

What is senna?

Answer 41

A stimulant laxative - precise mode of action not known but causes increased motility - often used in combination with docusate

Question 42

What is loperamide?

Answer 42

An opioid that doesnt cross the blood brain barrier used as an antidiarrhoeal

Question 43

What is simethicone?

Answer 43

a defoaming polymer used to coalesce gas bubbles so they can be more easily passed