Pharmacology of the GI Tract Flashcards
Dopamine is a ______
Dopamine is synthesised from ______
Neurotransmitter
Tyrosine
Does it increase or decrease gastric emptying?
Bloating + nausea + vomiting _____ gastric emptying
Constipation _____ gastric motility
Diarrhoea ______ lower gastric motility
Complete sentence
_______ reduce spasm to reduce pain
Increase
Increase
Decrease
Irritable bowel syndrome
Name the drugs that increase gastric motility
Domperidone (dopamine D2 receptor antagonist)
Metoclopramide (5-HT4 agonist)
Purgatives (for constipation)
- Both dopamine + metoclopramide used for bloating, nausea + vomiting*
- Stimulation of dopamine inhibits gastric motility causing post-prandial bloating + pain, contributing to nausea*
Domperidone has anti-emetic action
It peripherally increases gastric motility, emptying + _____.
It can prevent _____.
However it can cause ______ side effects
Duodenal peristalsis (contraction)
Bloating
Cardiac
Metoclopramide crosses blood-brain barrier + antagonise dopamine receptors; plus involved in movement
20% patients experience _____
10-20% can experience _____
What do the EU recommendin how long to use this drug?
drowsiness, restlessness, insomnia, fatigue
parkinson’s symptoms
short-term use (5 days) to prevent neurological side effects
Purgatives increases transit of food through GIT.
Examples include _____
Laxatives, faecal softeners, stimulant purgatives
Osmotic Laxatives include lactulose, macrogols + magnesium sulphate + hydroxide
What metabolises lactulose?
What does magnesium sulphate + hydroxide do?
What is the role of macrogols?
Metabolised by colonic bacteria into lactic + acetic acid
- Raise fluid volume osmotically - delayed effect approx 48 hours
Macrogols (movicol, idrolax) - retains fluid in bowel (e.g. bowel cleansing preps)
Magnesium sulphate + hydroxide remain in lumen + retain water
Examples of faecal softeners/lubricants
Docusate sodium - also has weak stimulant activity (stimulate GI Tract to contract more)
Liquid paraffin; arachis oil
Detergents - soften stools + ease defecation
Give examples of Stimulant laxatives
e.g. Senna extracts, bisacodyl, dantron
Senna
- enter colon + metabolised to anthracene
- stimulate GIT activity by irritation
Dantron
- GIT irritant
- Limited for terminal care due to being carcinogenic
Bisacodyl
- suppository
- rapid effect
- stimulate rectal mucosa (peristaltic function)
- stimulates electrolyte secretion - osmotic effect
What is Prucalopride?
What is it used for? and how does it do this?
Selective serotonin 5-HT4 receptor agonist
Chronic constipation in women
NICE guideline states women should use if other laxatives fail
Prucalopride stimulates 5-HT4 to release ACh to stimulate smooth muscle
What is Lubiprostone?
What is it used for + how does it do this?
Cl- channel activator
Increases intestinal fluid secretion, softening stool
For constipation
What is Linaclotide?
What is it used for? + how does it do this?
Guanylate cyclase-C receptor agonist (peptide)
Acts on epithelial cells
Increases intestinal fluid and transit
GI selective (not absorbed)
Used in IBS with constipation
How do you manage an opioid-induced constipation?
Avoid bulk-forming laxatives
Use an osmotic laxative (or docusate) + stimulant laxative
Advise patient laxatives can be stopped once stools are soft + easily passed again
What are the causes of diarrhoea?
bacterial/viral infection
rotaviruses causes damage to small bowel villi
amoebae + giardiasis cause diarrhoea
invasive bacteria e.g. campylobacter damage epithelium
cytotoxins damage mucosa
adhesive enteroxigenic bacteria adhere to brush border, leading to Cl- + Na+ secretion followed by water
What drugs cause diarrhoea?
antibiotics = alter gut flora leading to superinfection (clostridium difficile) which lead to colitis
orlistat = pancreatic lipase inhibitor used in obesity
misoprostol = via cAMP causing secretory diarrhoea
PPIs = suppress acid secretion too much allowing infection
acarbose + metformin
