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Clinical Pharmacology > 26) Drugs Affecting Gut Motility > Flashcards

26) Drugs Affecting Gut Motility Flashcards

1
Q

Describe the myogenic control of gastric motility:

A

Rhythmic contractions spread through gap junctions. Interstitial cells of Cajal are pacemaker

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2
Q

Describe the enteric neural control of gastric motility:

A

Stimulation of post-ganglionic cholinergic enteric nerves increases force of contraction of gut, through local nerves and plexuses

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3
Q

Where is Auerbach’s plexus located?

A

Between circular and longitudinal muscle layers

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4
Q

Where is Meissner’s plexus located?

A

Submucosa

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5
Q

Where is Henle’s plexus located?

A

Circular muscle adjacent to submucosa

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6
Q

Where is Cajal’s plexus located?

A

Circular muscle adjacent to longitudinal muscle

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7
Q

What is the intestino-intestinal inhibitory reflex?

A

Distension of one intestinal segment causes intestinal inhibtion

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8
Q

What is the ano-intestinal inhibitory reflex?

A

Distension of anus causes intestinal inhibition

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9
Q

What are the gastrocolic and duodenocolic reflexes?

A

Stimulates motility after material enters given organ

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10
Q

What hormones are involved in the control of gastric motility?

A

Gastrin, secretin, CCK, motilin, paracrine transmitters

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11
Q

Describe the pathway of emesis:

A

Triggers -> vomiting centre -> preliminary signs -> vomiting

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12
Q

Which areas are involved in the control of emesis?

A

Vestibular apparatus
Postrema on floor of 4th ventricle
Medullary centre

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13
Q

Give examples of anti-emesis drugs:

A 
Domperidone
Ondansteron
Metoclopramide
Hyoscine
Cyclizine
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14
Q

What is the mechanism of action of domperidone?

A

D2 antagonist, acts on psotrema on floor of 4th ventricle and increases gastric emptying

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15
Q

What are some side effects of domperidone?

A

Stimulates prolactin release

Rare: dystonia

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16
Q

What is the mechanism of action of ondansteron?

A

Serotonin antagonist - effective at postrema on floor of 4th ventricle and against vagal afferent nerves in GIT (stops initiation of vomiting)

17
Q

What are some side effects of ondansteron?

A

Headaches, constipation, flushing (IV)

18
Q

What is the mechanism of action of metoclopramide?

A

Dopamine antagonist at floor of 4th ventricle, serotonin antagonist. Causes increased gastric emptying and blocks vagal afferents

19
Q

What are some side effects of metoclopramide?

A

Extra-pyramidal reactions (dystonia), galactorrhoea

20
Q

What is the mechanism of action of hyoscine?

A

Direct antagonist of muscarinic cholinergic receptors

21
Q

What are some side effects of hyoscine?

A

Bradycardia, may get tolerance

22
Q

What is the mechanism of action of cyclizine?

A

Histamine antagonist and anti-muscarinic effects

23
Q

What are some side effects of cyclizine?

A

Prolonged QT interval, sedation

24
Q

What non-pharmacological treatment is there for constipation?

A

Increase fluid intake
Exercise
Fibre

25
Q

How do bulk laxatives work?

A

Insoluble and non-absorbable substances which distend gut and draw water in

26
Q

What are some contraindications to using bulk laxatives? What can be used instead in this case?

A

Adhesions/ulceration

Faecal softeners - lubricate and soften stool

27
Q

How do magnesium and sodium salts work in constipation treatment?

A

Cause water retention in small and large bowel to increase peristalsis

28
Q

How does lactulose work in constipation treatment?

A

Isn’t hydrolysed by enzymes so fermented by colonic bacteria forming acetic and lactic acid which have osmotic effect

29
Q

What is the mechanism of action of irritant laxatives?

A

Excitation of sensory nerve endings leads to water and electrolyte retention in lumen and peristalsis

30
Q

When are irritant laxatives indicated?

A

Rapid treatment e.g. faecal impaction and surgical prep

31
Q

What are some side effects of irritant laxatives?

A

Abdominal cramps

Repeated use: colonic atony, hypokalemia

32
Q

In general what laxatives should be given if patient has soft faeces?

A

Stimulant laxataives e.g. senna, glycerol

33
Q

In general what laxatives should be given if patient has hard faeces?

A

Osmotic laxatives e.g. movicol or bulk laxatives

34
Q

What are the 3 types of anti-diarrhoeal drugs?

A

Anti-motility
Bulk forming
Fluid adsorbents

35
Q

What is the mechanism of action of anti-motility drugs?

A

Act via opioid receptors in the bowel to reduce motility and allow more time for fluid absorption

36
Q

When should bulk forming drugs be used?

A

IBS, ileostomy

37
Q

What drug can be used in irritable bowel syndrome and why?

A

Mebeverine - relieves spasm of intestinal muscles

Bulk forming agents

Clinical Pharmacology (24 decks)

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