GI Drugs Flashcards
Name an anti motility drug for treating diarrhoea
Loperamide (an opiate analogue)
What adverse effect can occur if loperamide is given in IBD
Toxic mega colon
Example of a bulk forming anti diarrhoeal drug
Why is it useful in IBS
Ispaghula husk
Reduces both constipation and diarrhoea. Encourages normal bowel function
Give an example of a fluid absorbent
Comment on clinical use
Kaolin
Rarely prescribed
Describe GI enteric nervous system
Name 2 plexuses involved
What acts as pacemaker?
Autonomous. Allows intrinsic control of GI motility
Auerbach’s and Meissner’s plexuses
Interstitial cells of canal act as pacemakers
How do faecal softeners act as laxatives?
Lubricate and soften stool
What advantage do faecal softeners offer compared to other laxatives?
No risk of intestinal obstruction
However although safer, not as effective
Example of a faecal softener
Docusate sodium
Arachis oil
Name the 3 types of osmotic laxative
Magnesium & sodium salts eg phosphate enema
Lactulose syrup
Macrogols (powders)
Which of the osmotic laxatives acts most rapidly?
Phosphate enema (can be given PR for urgent relief) Effects are quick but severe
How does lactulose work?
Not absorbed but digested by colonic to produce lactate
Lactate causes osmotic effect.
Explain the mechanism behind bulk laxatives
Insoluble, non absorbable (eg veg. fibre)
Gut distension attempts to re establish normal bowel function
Example bulk laxative
Ispaghula husk
ADR of -bulk laxative -irritant/stimulant laxative
Bulk - flatulence
Irr/Stim - Abdo. Cramps
repeated use can cause colonic atony (constipation)
Hypokalemia
Name 2 irritant/stimulant laxatives
Senna Glycerol suppositories ( rectal mucosal action)
Explain MoA of irritant/stimulant laxatives
Excite sensory nerve endings
Leads to electrolyte , water retention in bowel lumen
Peristalsis
What 2 structures close during emesis?
Pyloric sphincter
Glottis
What 3 structures are inv in the emetic control?
Vestibular apparatus
Medulla (CTZ and vomiting centre)
Postrema on floor of 4th ventricle
Name 4 hormonal receptors blocked by anti-emetic drugs
Dopamine D2
Serotonin (5HT) 3
Muscarinic (ACh)
Histamine H1
What is the mechanism of Hycoscine?
Muscarinic cholinergic receptor antagonist
How does Ondansteron act?
5HT3 receptor antagonist
What receptor does Domperidone act on?
D2 (dopamine) antagonist
What receptor does Cyclizine act on?
H1 receptor antagonist
Ondansteron use
CHEMO and radiation induced w CORTICOsteroids even more effective
