123 - Antiemetic, Antidiarrhoeal Drugs Flashcards
Example of a D2 antagonist
Metaclopramide
Metaclopramide effects
Increases contractions in upper GIT, which makes stomach empty more quickly.
5HT4 receptor stimulation -> ACh release (Metaclopramide).
Metaclopramide also has dopaminergic effects. Blocks dopamine in the gut.
D2 antagonist
Is metaclopramide a reversible or irreversible antagonist?
Reversible.
If taken long-term, D2 antagonists can have permanent effects (severe side effects - extrapyramidal side-effects - uncontrollable muscle movements of your lips, tongue, eyes, face, arms, or legs)
Example of a 5HT3 antagoinst
Ondansetron
Ondansetron side effects
Constipation.
Headaches.
What are metaclopramide and ondansetron used to treat?
Nausea, vomiting
Endogenous compound that stimulates NK1 receptors
Substance P
Example of a neurokinin-1 receptor antagonist
Aprepitant
How is aprepitant administered?
Always in combination with another drug
Example of two add-on drugs for nausea, emesis
1) Aprepitant
2) Dexamethasone (glucocorticoid)
What are neurokinin-1 receptor antagonists used for?
Anti-emetic
Bulking agents
Hydrophilic colloids.
Indigestible vegetable fibre that increases faecal water retention, therefore increasing volume of faeces.
Increases normal reflex bowel activity.
Examples of bulking agents
Bran, Psyllium, Ispaghula husk, Sterculia.
Psyllium is the most important to remember
Side effects of bulking agents
Water loss.
If constipation is slow-transit, or is opioid-induced, can just contribute to faecal mass, increase impaction.
Increased flatulence.
Does chronic use of stimulant laxatives cause an atonic colon?
Maybe causes permanent atonia of colon, but it is not clear
Four groups of laxatives 1 2 3 4
1) Bulking agents
2) Faecal softeners and lubricants
3) Osmotic laxatives
4) Stimulant laxatives
Example of a faecal softener and lubricant
Docusate.
Docusate
1
2
3
Faecal softener and lubricant.
Frequently prescribed for people on opioids.
A detergent, so increases mixture of water into faeces.
Danger of using paraffin wax for constipation
Can adsorb fat-soluble vitamins.
Can be accidentally inhaled, cause issues in the lungs.
Types of osmotic laxatives 1 2 3 4
1) Saline laxatives
2) Disaccharide hydrophilic colloid
3) Polyols
4) Macrogols or polyethylene glycols
Example of an osmotic laxative
Magnesium salts (a saline laxative)
How do disaccharide (galacto-fructose) hydrophilic colloids work?
Draw water into faeces through osmosis
Which laxative is included in some confectionary as an artificial sweetener?
Polyols
Most-potent laxatives
Stimulant laxatives
How do stimulant laxatives work?
Precise mode of action is not known but may stimulate colonic myenteric nerve plexuses,
irritate intestinal mucosa or by direct sensory nerve ending irritation → increase motility.
May also reduce net reabsorption of water and electrolytes.
Example of a stimulant laxative
Senna
Another name for stimulant laxative
Irritant laxative
Types of antidiarrhoeal drugs
1
2
3
1) Opioids
2) Musculotropic antispasmodic
3) Muscarinic R antagonists
Example of an opioid used to reduce diarrhoea
Loperamide
How do opioid antidiarrhoeals work (basically)
Antagonise mu opioid receptors, blocking ACh release.
Why doesn’t loperamide cause the CNS effects of other opioids?
Doesn’t cross blood brain barrier
Musculotropic antispasmodic
Mebeverine
Example of a muscarinic R antagonist
Hyoscine butylbromide
Anti-flatulence drug
Simethicone
Simethicone effect
Defoaming polymer, that changes surface tension of small gas bubbles, allowing them to join into larger gas bubbles which can be passed more easily.
