Flashcards in GI examination - Peptic ulcers, laxatives, constipators Deck (39)
What is the mechanism of action of omeprazole?
Prevents H+ ions being pumped into parietal cell canaliculi by targeting ATPase
Only works if you eat (you need proton pumps working for it to bind)
What is the mechanism of action of histamine
Removes the amplification of Gastrin/Ach signal by acting as a Histamine Receptor Antagonist
How do you treat Gord?
o H2 Receptor Antagonists
Give four adverse reactions to PPIs
o GI upset
o Risk of gastric atrophy with long-term treatment
Give four H2 receptor antagonists
What is h.Pylori triple therapy
Proton pump inhibitor
Two antibiotics - Amoxicillin/Clarithromycin
When are PPIs used?
Short term treatment of peptic ulcers
Eradication of H. Pylori (part of triple therapy)
Zollinger-Ellison Syndrome (Gastrin secreting pancreatic tumour)
What is the mechanism of action of PPI?
Irreversibly inhibit Na/K-ATPase that is responsible for proton secretion from parietal cells.
Give the main ADRs associated with PPI
GI upset, nausea
Give a key DDI of omeprazole
Omeprazole is a CYP450 enzyme inhibitor
Avoid use with patients being treated with Warfarin, Phenytoin etc.
How long do PPI take to work?
PPI action is delayed as not all pups are active all of the time. Maximum efficacy is after 2-3 days and only works if you eat as existing acid has to be pumped out into intestine.
What are the two indications for H2 antagonists?
Peptic ulcer disease and GORD
How do H2 antagonists work?
Competitively antagonist H2 receptors, blocking the amplifying action of Histamine on Parietal cells
What are four key ADRs for H2 antagonists?
What is a key DDI of H2 antagonists?
Cimetidine is a CYP450 enzyme inhibitor
Avoid use with patients being treated with Warfarin, Phenytoin etc
When are H2 antagonists given?
At night when food buffering at lowest
Name four types of laxative
When would you give bulk laxative?
What is the mechanism of action of bulk laxatives
Increases the volume of non-absorbable solid residue in the gut , distending the colon and stimulating peristaltic movements
When should you not use a bulk lax?
Intestinal obstruction (Adhesions, ulceration)
What are three adverse reactions to bulk laxatives?
Name an osmotic laxative
What is the mechanism of action of osmotic laxatives
Increase water content of the bowel via osmosis
Lactulose – Disaccharide (galactose/fructose) that cannot be hydrolysed by digestive enzymes. The fermentation of lactulose by colonic bacteria gives acetic and lactic acid. This has an osmotic effect
When should you not use osmotic laxative?
Give four ADRs of osmotic laxatives
Caution required to prevent intestinal obstruction
Give an anti-diarrhoeal
When should anti-diarrhoeals NOT be used
Inflammatory bowel disease - Toxic mega colon
What is the mechanism of action of codeine anti-diarrhoeals
Act on opioid receptors in the bowel
Reduce motility (increase time for fluid reabsorption)
Increase anal tone and reduce sensory defecation reflex
Anti-diarrhoeals adverse reactions (5)
Nausea, vomiting, abdominal cramps, constipation drowsiness
What is one anti-diarrhoeal with super good morphine effects`
Imodium, can't penetrate BBB, super effective
How do bulk forming anti-diarrhoeals work?
Relatively small amount of faecal fluid influences composition.
What is IBS?
o Abdominal Pain
o Alteration of Bowel Habits
Give process of vomiting
o Pyloric sphincter closes while the cardia and oesophagus relax
o Gastric contents propelled by contraction of abdominal wall and diaphragm
o Glottis closes with elevation of soft palate, preventing entry of vomit into the trachea and Nasopharynx
If vomiting is due to alcohol, or patient has a cranial nerve lesion they are at a higher risk of aspiration as this does not work properly
Give 3 types of anti-emetics
Dopamine receptor antagonist
Muscarinic receptor antagonist
What is the mechanism of action of vomtiing
Things (medication, smell, touch, raised ICP, stomach) stimulate postrema on floor of 4th ventricle
Vestibular apparatus disturbance
Both stimulate medullary centre, whcih releases aCh, histamine and serotonin, which causes vomiting
How do dopamine receptor antagonists work?
Acts on the Postrema on the floor of the 4th ventricle
Acts on the stomach to increase the rate of gastric emptying
What are three ADRs of dopamine receptor antagonists
Stimulates prolactin release
Metoclopramide – extra-pyramidal reactions (dystonia) occur in 1%, therefore is avoided in Parkinson’s disease
Galactorrhoea – Can induce pro-lactin
What is the mechanism of action of serotonin antagonists?
5-HT is released into the gut, reducing Vagus activity, therefore effective at deactivating the vomiting centre (the Postrema on the floor of the 4th ventricle)
Blocks Serotonin receptors in Chemoreceptor Trigger Zone