Drugs Affecting the Gastrointestinal System Flashcards
What are some causes of peptic ulcers?
H. pylori, NSAIds, smoking, caffeine, alcohol, glucocorticosteroids, bile
Why are prostaglandin E2 and I2 protective against ulcers?
The stimulate secretion of mucus and bicarbonate and increase mucosal blood flow to remove stray H+ ions
What is the action of H2 receptor antagonists?
Block effects of gastrin, acetylcholine and histamine on parietal cells
How do parietal cells secrete acid?
With a proton pump which exchanges H+ for K+ with an ATPase
What is omeprazole?
A proton pump inhibitor
What is esomeprazole?
A proton pump inhibitor
What is ranitidine?
An H2 receptor antagonist
What is magnesium hydroxide?
An antacid - used to neutralise stomach acid
What is a contraindication of antacids?
Kidney problems
What are some side effects of antacids?
diarrhoea and constipation
Why do antacids cause rebound acidity?
Because they stimulate gastrin release
What are cytoprotective agents?
They coat the ulcer site to protect it from the acid
What is hyoscine butylbromide?
a muscarinic receptor antagonist - to reduce motility
What is mebeverine?
a non specific muscle relaxant
What is misoprostol?
A synthethetic prostaglandin E analogue - to increase mucus secretion and mucosal blood flow and decrease acid secretion
What the contraindication of misoprostol?
Pregnancy - will induce motility in uterus and cause an abortion
What are other side effects of misoprostol?
colic and diarrhoea
What are two inputs to the vomiting centre?
the chemoreceptor trigger zone and the vestibular apparatus
What are the receptors for the chemoreceptor trigger zone to the vomiting centre?
D2 receptors and 5HT3 receptors
What are the receptors for the vestibular apparatus to the vomiting centre?
H1 receptors and muscarinic receptors
What is hyoscine hydrobromide?
a muscarinic receptor antagonist that crosses the blood blood brain barrier for motion sickness
What are the side effects of hyoscine hydrobromide?
anti SLUD - dry mouth, dry eyes, urinary retention, constipation
What is promethazine?
An H1 receptor antagonist for motion sickness (phenergen)
What is metoclopramide?
A D2 receptor antagonist for vomiting and nausea associated with the chemoreceptor trigger zone - also a weak 5HT3 antagonist and a potent 5HT4 agonist - facilitates gastric emptying via increased ACh (but not diarrhoea)
What is the effect of facilitating gastric emptying in metoclopramide?
changes the absorption of other drugs
What is prochlorperazine?
A D2 receptor antagonist for vomiting and nausea associated with the chemoreceptor trigger zone
What are the side effects of D2 receptor antagonists?
extra pyramidal side effects - motor movements like parkinsons and sometimes irreversible tardive dyskinesia
What is ondansetron?
A 5HT3 receptor antagonist - used for vomiting and nausea associated with the chemoreceptor trigger zone - blocks both receptors on the the chemoreceptor trigger zone and on vagal afferents which receive signals from the enterochrommaffin cells
What are the side effects of 5HT3 receptor antagonists?
very few - minor headache and constipation
What is aprepitant?
An NK1 receptor antagonist - a substance P antagonist - substance P is found in high concentrations in the vomiting centre in the brain
What is dexamethasone?
A glucocoritcosteroid used to treat nausea and vomiting although not technically an antiemetic
What is rabione?
A synthetic cannabinoid - used as an antiemetic
What is apomorphine?
A dopa receptor agonist - a very potent emetic
What causes constipation?
certain drugs e.g. opioids, lifestyle factors, inadequate dietary fibre intake, inappropriate bowel habits, inadequate activity, spinal injury, dementia, depression, hypothyroidism
Apart from constipation, when else are laxatives used?
Before a colonoscopy, hernias, prolapsed rectum
What are bulking agents?
indigestible vegetable fibre taken with water to stimulate normal reflex bowel movements
What is docusate?
A faecal softener - acts as an emulsifying agent
What is liquid paraffin?
A faecal lubricant - may cause loss of fat soluble vitamins
What is magnesium sulphate?
an osmotic laxative - causes osmotic fluid retention to get more mass and more distension
What is bisacodyl?
A stimulant laxative - precise mode of action not known but causes increased motility
What is senna?
A stimulant laxative - precise mode of action not known but causes increased motility - often used in combination with docusate
What is loperamide?
An opioid that doesnt cross the blood brain barrier used as an antidiarrhoeal
What is simethicone?
a defoaming polymer used to coalesce gas bubbles so they can be more easily passed
