Pharmacology go the GI tract Flashcards
What are the synthesis pathway of Dopamine and 5-HT?
Dopamine - Tyrosine, DOPA, dopamine, noradrenaline, adrenaline
5-HT - tryptophan, 5-hydroxytrytophan, 5-hydroxytryptamine
What are purgatives?
increase transit of food through GIT (laxative, faecal softeners)
How does Lactulose work?
metabolised by colonic bacteria into lactic and acetic acid, raise fluid vol osmotically
How do macrogols work?
sequester (isolate) fluid in bowel
How do magnesium sulphate & mag hydroxide work?
remain in lumen & retain water
What are the osmotic laxatives?
lactulose, macrogols, mag sulphate& mag hydroxide
What are the faecal softeners/lubricants?
docusate sodium, liquid paraffin, arches oil, detergents (soften stools & ease defecation)
What are the stimulant laxatives and how do they work?
Senna extracts (stimulate GIT activity by irritation)
Dantron (same as senna)
Bisacodyl (stimulate rectal mucosa, preristaltic action, stimulates electrolyte secretion, osmotic effect)
What pro kinetic drugs are used to increase GI motility and how do they work?
domperidone - D2 receptor antagonist closes gastro-oesophageal sphincter increase gastric emptying into duodenum
metoclopamide - 5-HT4 agonist/antagonist
What are the side effects of domperidone & metoclopramide?
dom - cardiac side effects
met - drowsiness, restlessness, insomnia, fatigue
What are anti-motility agents?
opiods, antimuscarinic agents
How do opioids work?
reduce tone and peristalsis movement, inhibit ACh release by causing hyper polarisation so prevents calcium channel opening and release of ACh
Why are antimuscarinic agents not primary therapy of diarrhoea? what are the side effects?
due to side effects of other muscarine receptors around body
dry mouth, dry eyes, dry skin, tachycardia (increase heart rate)
What should patents with long term opioids be prescribed with?
laxatives
What happens with tricyclic antidepressants, antipsychotics and sedating antihistamines?
anticholinergic effects - constipation
When and why is methylnaltexone used?
opioid receptor antagonist, treatment for opioid induced constipation in patients receiving palliative care
When is plucalopride used and how does it work?
constipation in women, selective serotonin 5-HT4 receptor agonist
When is Linaclotide used and how does it work?
constipation, guanylate cyclase- C receptor agonist, acts on epithelial cells increasing intestinal fluid secretion & transit
What is Lubiprostone and how does it help constipation?
Chloride channel activator, increases intestinal fluid secretion
What are the causes of diarrhoea?
bacterial or viral infection
rotaviruses cause damage to small bowel villi
amoebae & giardia
Which drugs cause diarrhoea and how?
antibiotics - alter gut flora - infection
orlistat - pancreatic lipase inhibitor used in obesity
misoprostol - via cAMP causing secretory diarrhoea
PPIs - suppress acid secretion - infection
What are the treatment of Diarrhoea?
ORT oral rehydration therapy (electrolytes)
opiates - decrease gut motility allowing reabsorption of water and reducing water in stools
