Pharmacology go the GI tract

Question 1

What are the synthesis pathway of Dopamine and 5-HT?

Answer 1

Dopamine - Tyrosine, DOPA, dopamine, noradrenaline, adrenaline
5-HT - tryptophan, 5-hydroxytrytophan, 5-hydroxytryptamine

Question 2

What are purgatives?

Answer 2

increase transit of food through GIT (laxative, faecal softeners)

Question 3

How does Lactulose work?

Answer 3

metabolised by colonic bacteria into lactic and acetic acid, raise fluid vol osmotically

Question 4

How do macrogols work?

Answer 4

sequester (isolate) fluid in bowel

Question 5

How do magnesium sulphate & mag hydroxide work?

Answer 5

remain in lumen & retain water

Question 6

What are the osmotic laxatives?

Answer 6

lactulose, macrogols, mag sulphate& mag hydroxide

Question 7

What are the faecal softeners/lubricants?

Answer 7

docusate sodium, liquid paraffin, arches oil, detergents (soften stools & ease defecation)

Question 8

What are the stimulant laxatives and how do they work?

Answer 8

Senna extracts (stimulate GIT activity by irritation)
Dantron (same as senna)
Bisacodyl (stimulate rectal mucosa, preristaltic action, stimulates electrolyte secretion, osmotic effect)

Question 9

What pro kinetic drugs are used to increase GI motility and how do they work?

Answer 9

domperidone - D2 receptor antagonist closes gastro-oesophageal sphincter increase gastric emptying into duodenum
metoclopamide - 5-HT4 agonist/antagonist

Question 10

What are the side effects of domperidone & metoclopramide?

Answer 10

dom - cardiac side effects

met - drowsiness, restlessness, insomnia, fatigue

Question 11

What are anti-motility agents?

Answer 11

opiods, antimuscarinic agents

Question 12

How do opioids work?

Answer 12

reduce tone and peristalsis movement, inhibit ACh release by causing hyper polarisation so prevents calcium channel opening and release of ACh

Question 13

Why are antimuscarinic agents not primary therapy of diarrhoea? what are the side effects?

Answer 13

due to side effects of other muscarine receptors around body
dry mouth, dry eyes, dry skin, tachycardia (increase heart rate)

Question 14

What should patents with long term opioids be prescribed with?

Answer 14

laxatives

Question 15

What happens with tricyclic antidepressants, antipsychotics and sedating antihistamines?

Answer 15

anticholinergic effects - constipation

Question 16

When and why is methylnaltexone used?

Answer 16

opioid receptor antagonist, treatment for opioid induced constipation in patients receiving palliative care

Question 17

When is plucalopride used and how does it work?

Answer 17

constipation in women, selective serotonin 5-HT4 receptor agonist

Question 18

When is Linaclotide used and how does it work?

Answer 18

constipation, guanylate cyclase- C receptor agonist, acts on epithelial cells increasing intestinal fluid secretion & transit

Question 19

What is Lubiprostone and how does it help constipation?

Answer 19

Chloride channel activator, increases intestinal fluid secretion

Question 20

What are the causes of diarrhoea?

Answer 20

bacterial or viral infection
rotaviruses cause damage to small bowel villi
amoebae & giardia

Question 21

Which drugs cause diarrhoea and how?

Answer 21

antibiotics - alter gut flora - infection
orlistat - pancreatic lipase inhibitor used in obesity
misoprostol - via cAMP causing secretory diarrhoea
PPIs - suppress acid secretion - infection

Question 22

What are the treatment of Diarrhoea?

Answer 22

ORT oral rehydration therapy (electrolytes)

opiates - decrease gut motility allowing reabsorption of water and reducing water in stools