CPTP 2.11 Drugs and the GI tract Flashcards
Two types of peptic ulcer?
Gastric ulcer and duodenal ulcer
What protects mucosa?
prostaglandin
mucus
bicarbonate
mucosal blood flow
what damages mucosa?
acid
pepsin
NSAIDs
H.pylori
What stimulates gastric acid secretion?
histamine (binds to H2 receptor)
gastrin (binds to CCK B receptor and trigger histamine release)
ACh (triggers histamine release)
They all induce insertion of K+/H+ ATPase
Five types of drugs used in peptic ulcer disease
antimicrobial drugs PPIs H2 receptor antagonist prostaglandins antacid
Antimicrobial agents
- combination of antimicrobial drugs required
- current treatment (triple therapy); PPI + Clarithromycin + Amoxicillin/metamidazole
what is PPI?
Proton pump inhibitor
e.g. Omeprazole
Mechanism of PPIs?
Administered as a prodrug with an enteric coating to prevent degradation by the stomach acid. Prodrugs passes into the acidic canaliculus
The coating is removed in the alkali environment in the duodenum and become active, sulfenamide form.
Sulfenamide forms covalent bond with H+/K+ ATPase irreversibly
Metabolised by the CYP enzymes in the liver and then excreted
H2 receptor antagonist
rantidine
pharmacodynamics of
H2 receptor antagonist
competitive antagonist
administration orally
kidney exrete parent drugs and metabolites by filtration and renal tubular secretion
antacid
weak bases that react with gastric acid to form water and a salt to diminish gastric acidity
aluminium hydroxide Al(OH)3
Magnesium carbonate
administered as liquid/oral tablets
for quick relief
Antimotility drugs
Opioid e.g. Loperimide
Oral or liquid administration
act on opioid receptors to inhibit ACh release and reduce motility
control diarrhoea
adsorbent
e.g. methylcellulose
absorb intestinal microorganisms (when used as an adsorbent)
absorb water and increase stool bulk (when used as anti-constipation drug)
Agents that modify fluid transport
e.g. bismuth subsalicylate
stimulates absorption of fluids and electrolytes by the intestinal wall (anti-secretory action)
reduces hypermotility of the stomach
Drugs to treat diarrhoea
antimotility drugs
absorbents
agents that modify fluid transport
type of drug used to treat constipation?
Laxative
Four types of Laxatives
Bulk-forming drugs e.g. ispaghula husk
Osmotic laxatives e.g. lactulose
faecal softeners e.g. liquid paraffin
Stimulant laxatives e.g. senna
Bulk-forming drugs
e.g. ispaghula husk
absorb water and increase stool bulk -> increase intestinal distension, thereby increasing peristaltic activity
colonic bacteria use the hydrated material as a metabolic substrate -> increase in the bacterial cell mass with a consequential softening of the faeces
takes 1-3 days
Osmotic laxatives
e.g. lactulose
Non absorbable compounds that hold water in the intestines by osmosis. This distends the bowel, increasing intestinal activity
take up to 24 hours to act
Faecal softneners
e.g. liquid paraffin
agents become emulsified with the stool and soften/lubricate it for easy passage
Stimulant laxatives
e.g. senna
administered in an innocuous form
converted to their active forms by bacteria in the colon
They irritate the mucosa, inducing low grade inflammation, which stimulates peristalsis and promotes accumulation of water and electrolytes
How is gut motility controlled?
ENS
Submucosal (Meissner) plexus controls ion and fluid transport
Myenteric (Auerbach) plexus control motility
How the sympathetic and parasympathetic nervous system modulate the ENS in the gut
Para- releases ACh that stimulate ENS to release ACh for gut SM constraction
Sym- release noradrenaline that inhibits ENS, so no ACh release. Inhibitory.
Drug used to treat IBS
Antispasmodics
e.g. hyoscine and mebeverine
