Drugs Affecting Gut Motility Flashcards Preview

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Flashcards in Drugs Affecting Gut Motility Deck (68):
1

What are the types of physiological control of gut motility

Myogenic
Neurological
Hormonal

2

What is myogenic control of gut motility

Rhythmic contractions of intestinal smooth muscle
Interstitial cells of Cajal act as pacemaker cells
Depolarisations spread through gap junctions

3

What is neuronal control of gut motility

Enteric Plexus - network of autonomic fibres in intestinal wall
Cholinergic nerves increase force of contraction
Non-adrenergic inhibitory nerves decrease contraction

4

What is hormonal control of motility

Peptide hormones secreted by endocrine cells in intestinal mucosa
CCK
Secretin
Gastrin
Paracrine - prostaglandin, histamine, somatostatin

5

What are the steps of vomiting reflex

Contraction of pyloric sphincter
Relaxation of cardia and oesophagus
Contraction of abdominal wall and diaphragm
Expulsion of gastric contents

6

What are triggers of vomiting reflex

RICP
Vestibular apparatus : rotational movement
Chemoreceptor Trigger Zone: toxins, Drugs, electrolytes
Higher cortical centres: pain, sight, smell
GI tract: stretch, inflammation

7

What is vomiting centre

Area in medulla responsible for control+coordination of muscles involved in vomiting reflex

8

What is Area Postrema

Part of vomiting centre containing CTZ
Located in base of 4th ventricle
Thus Outside BBB and exposed to blood vomiting triggers in peripheral circulation

9

What are neurotransmitters involved in vomiting reflex

Vestibular apparatus: H1 receptor
CTZ: D2, 5HT3
GI: D2
Vomiting centre: ACh, H1, 5HT3

10

What are types of antiemetic drugs

D2 antagonist
5HT3 antagonist
ACh antagonist
H1 antagonist
Cannabinoids
Benzodiazepines

11

Give examples of D2 antagonists

Domperidone
Metoclopromide
Phenothiazine

12

What is mechanism of action of D2 antagonists

Antagonise D2 receptor at Area postrema
Antagonise D2 at stomach - slow gastric emptying

13

What are indications of D2 antagonists

Acute N+V (esp if L-dopa induced)
PONV

14

What are side effects of D2 antagonists

Galactorrhoea (loss of dopaminergic inhibition of prolactin release)
Dystonia (rare)

15

What are PK properties of D2 antagonists

Oral, PR
Extensive first pass metabolism
Does not cross BBB

16

Give examples of 5HT3 antagonists

Ondansetron
Granisetron

17

What is mechanism of action of 5HT3 antagonists

Antagonise 5HT3 at area postrema
Antagonise 5HT3 receptors of vagus afferent fibres in GIT

18

What are indications of 5HT3 antagonists

Chemotherapy (1st line)
Radiation sickness
PONV (esp opioid induced)

19

What are side effects of 5HT3 antagonists

Headache
Constipation
Flushing

20

How are 5HT3 antagonists administered

IV
Enhanced effect if given with dose of corticosteroids

21

What is mechanism of action of metoclopramide

Antagonise D2 at area postrema
Antagonise D2 at stomach - slow gastric emptying
Anticholinergic (GI)
Antagonise 5HT3 at vagal afferent fibres of GIT

22

What are indications of metoclopramide

Acute N+V (first line)
PONV (gastric cause)

23

How is metoclopramide administered

Oral
TDS - T1/2 4hrs

24

What are side effects of metoclopramide

Extrapyramidal side effects - CI in PD
Galactorrhoea

25

Give examples of ACh antagonists

Hyoscine

26

What is mechanism of action of ACh antagonists

Antagonise mAChR at vestibular apparatus

Anticholinergic at GIT - inhibit gastric secretions

27

What are indications of ACh antagonists

Motion sickness
N+V in Obstruction

28

What are side effects of ACh antagonists

Systemic anticholinergic effects

29

Give examples of H1 antagonists

Cyclizine
Promethiazine

30

What is mechanism of action if H1 antagonists

Antagonise H1 at vomiting centre

31

What are indications of H1 antagonists

Acute N+V

32

What are side effects of H1 antagonists

Sedation
QT prolongation

33

What are principles of management of constipation

Lifestyle: increase fluids, fibre, exercise
Treat underlying cause: dehydration, DM, PD, opioids, diuretics, anticholinergics
Pharmacological: laxatives

34

What are the types of laxatives

Stimulant (soft stool)
Osmotically active (hard stool)
Bulking agent (hard stool)
Faecal softeners (hard stool)

35

Give examples of bulking laxatives

Ispaghula
Cellulose

36

What is mechanism of action of bulking agents

Insoluble agents draw water in
Bowel distension
Stimulate stretch receptors
Stimulate peristalsis
Takes days to take effect

37

What are indications of bulking agents

Hard stools

38

What are side effects of bulking agents

Risk of obstruction - CI in adhesions and ulcers
Dehydration
Flatulence

39

Give examples to faecal softeners

Arachis oil
Glycerol

40

What is mechanism of action of faecal softeners

Lubricate stool
Assist evacuation of stool

41

What are indications of faecal softeners

Hard stools
Adhesions
Anal fissure
Haemorrhoids

42

What are side effects of faecal softeners

Safe
But not effective

43

Give examples of osmotically active laxatives

Mg, Na salts
Lactulose
Macrogol (Movicol)

44

What is mechanism of action of osmotically active laxatives

Draw water into lumen
Cause bowel distension
Stimulate stretch receptors in bowel wall
Stimulate peristalsis

45

What are indications of Mg and Na salts

Urgent relief
Resistant constipation

46

How is Mg and Na salts administered

PR

47

What is mechanism of action of lactulose

Broken down by colonic flora into acetic and lactic acid
Acetic and lactic acid are osmotically active

Acetic and lactic acid bind+trap ammonia in gut

48

What are indications of lactulose

1st line hospital constipation
Liver failure - prevent encephalopathy

49

Give examples of stimulant laxatives

Senna
Codanthramer
Bisacodyl

50

What is mechanism of action of stimulant laxatives

Stimulate enteric plexus
Stimulate peristalsis directly
Cause electrolyte and fluid retention, stimulate stretch receptors thus peristalsis

51

What are indications of stimulant laxatives

Urgent treatment:
Surgical preparation
Impaction

52

What are side effects of stimulant laxatives

Abdominal cramps
Hypokalaemia
Colonic atony (chronic use)
Melenosis Coli (pigmentation; overuse)

53

What are principles of management of diarrhoea

Treat cause: infection, IBD, IBS, bile, pancreatic enzymes
Supportive: fluids, electrolyte replacement
Anti-diarrhoea Drugs: for symptom relief

54

Give examples of anti-motility drugs

Loperamide

55

What is mechanism of action of loperamide

Opioid analogue
Bind to opioid receptors on bowel wall
Decreased motility
Increased transit time
Increased water absorption
Increased anal tone

56

What are indications of loperamide

Chronic diarrhoea

57

What are side effects of loperamide

Risk of toxic megacolon - CI in IBD

58

What are types of anti-diarrhoea drugs

Anti-motility
Bulk-forming laxatives
Cholestyramine
Pancreatic enzymes

59

What is mechanism of action of bulk forming agents for diarrhoea

Absorb water

60

What are indications of bulk forming agents for diarrhoea

IBS with chronic diarrhoea+constipation

61

What is mechanism of action of cholestyramine

Bile acid sequestration

62

What are indications of cholestyramine

Diarrhoea secondary to bile acid malabsorption:
Crohn’s
Ileal resection

63

Give examples of pancreatic enzymes

Pancreatase

64

What are indications of pancreatase

Diarrhoea secondary to malabsorption from lack of pancreatic enzymes:
Chronic pancreatitis
Cystic fibrosis

65

What is IBS

Chronic and relapsing disorder of GI function without physical/biochemical abnormality

66

What is the diagnostic criteria of IBS

6 months of:
Abdominal pain relieved by defecation
Abdominal bloating
Change in bowel habit: Constipation, diarrhoea

67

What are principles of management of IBS

Lifestyle: increase fluid, limit fibre, limit caffeine
Diarrhoea: loperamide
Constipation: ispaghul
Pain: peppermint oil, mebeverine

68

What is mechanism of action of mebeverine

Antispasmodic agent
Anticholinergic effects on gut wall
Relax intestinal smooth muscle
Relieves pain from muscle spasms