Pharma Basis For Gastric Treatment Flashcards
What are the effects of metoclopramide on gastric motility and emptying?
Metoclopromide has mixed effects:
Inhibits pre- and post-synaptic dopamine (D2) receptors. This ↑ Ach release. This ↑ peristalsis) and ↑intragastric pa (due to ↑ LOS tone) which accelerates gastric emptying
Inhibits 5-HT3 receptors (CNS), which inhibits vomiting.
How does dopamine affect the gut?
Dopamine has relaxant effects on the gut by activating D2 receptors in the lower oesophageal sphincter and stomach, which inhibits Ach release
Dopamine acts on different dopamine receptors
Overall, dopamine has mixed effects on the gut – may induce contraction in the proximal, but relaxation in the distal small intestine
What is Metoclopramide useful for?
Gastrointestinal reflux
Symptoms of gastroparesis
Stimulates gastric motility
Accelerates gastric emptying
Anti-emetic effects via central pathways
Nausea
What are antispasmodic agents?
Antispasmodic agents are muscarinic receptor antagonists: they inhibit parasympathetic activity which ↓ spasm in the bowel and relaxes GI smooth muscle
Eg: propantheline, dicloxerine, Mebeverine
Propantheline= antimuscarinic, useful in IBS and diverticular disease.
Mebeverine potently blocks intestinal peristalsis. Eases IBS-like cramps
What are the causes of constipation?
↓ motility of large intestine
Old age
Diet
Inactivity
Drugs (polypharmacy)
Damage to enteric nervous system of colon (-may affect the initiation of vago-vagal reflex)
What factors can increase colonic motility?
↑ fibre, cellulose and complex polysaccharides
Bran, some fruits and vegetables with high fibre
Laxatives, but excessive use → ↓ responsiveness
Mineral oil – lubricates faeces
Castor oil – stimulates colon motility
Increased colonic motility increases gut distension and initiates the vago vagal reflex, improving constipation.
What are the alarm signs in constipated patients?
Acute onset constipation in older individuals
Weight loss (10lb)
Blood in the stool
Anaemia
Family history of colon cancer or inflammatory bowel disease
What are Purgatives, specifically bulk forming laxatives?
Purgatives inc laxatives, faecal softeners & stimulant
Bulk-forming laxatives: methylcellulose, plant gums (e.g. agar, linseed, bran)
They retain water in gut lumen, causing distention and therefore peristalsis, but take a few days to work
Increase the stool’s solid content
Side effects: bloating and flatulence
What are osmotic laxatives?
Osmotic laxatives: lactulose
↑ fluid volume in the bowel lumen by osmosis
↑ transfer of gut contents into the intestine
Increases volume of gut content entering the colon, causing distension and purgation/pooping in 1hr
High doses → flatulence, cramps, diarrhoea, vomiting
What is lactulose?
Lactulose is a carbohydrate source for lactobacilli and bifidobacteria
It ↑ growth of colonic bacteria
What are the treatments for diarrhoea?
Maintain fluid and electrolyte balance via oral rehydration therapy
Use of anti-infectives:
Campylobacter sp is the cause of gastroenteritis in the UK. Use erythromycin or ciprofloxacin in severe infections
Use of non-microbial anti-diarrhoeal agents
Use of anti-motility drugs: adsorbents and agents that modify fluid and electrolyte transport
What is the result of acute diarrhoeal diseases?
Diarrhoea → ↑ motility of GIT, with ↑ secretion and ↓ absorption of fluid → ↓ electrolyte (Na+) and H2O
Cholera toxins → loss of gut contents
Give specific drugs for the treatment of diarrhoea
Loperamide: Selective on GIT, decreases passage of faeces and illness duration
Codeine & loperamide: Anti-secretory action, ↓ intestinal motility
Bismuth subsalicylate: Decreases fluid secretion in bowel;
Safe for children over 12, but not if they have chicken pox, flu
May cause tinnitus and blackening of stool
What is the mechansim of action of loperamide?
An opioid receptor agonist. Doesn’t cross BBB, no CNS effects
Binds to the opioid receptor of the myenteric plexus (controlling motility and secretion) of the large intestine.
This inhibits gastric emptying, increases sphincter tone, blocks peristalsis
A spasmolytic agent. Reduces force and speed of colonic movement by:
Increasing haustral mixing of the proximal colon
Inhibiting propulsive mass movement of the distal colon
