13.1 GI Motility Drugs Flashcards
What can cause vomiting?
Problems with the vestibular system Drug Induced - Post Op, Chemotherapy Alcohol Pregnancy Unpleasant Stimuli - Smells Infections - Salmonella Raised ICP
What areas of the brain are involved in vomiting?
The Area Postrema
The Medullary Centres
The Vestibular Areas
What Neurotransmitters are involved in vomiting?
ACh
Histamine
Serotonin
Dopamine
What are the 4 classes of Drug we use to treat vomiting?
D2 antagonists
ACh (muscarinic) antagonists
5HT antagonists
Histamine antagonists
How do D2 antagonists work?
Examples:
When are they used?
Act on the area postrema
Metoclopramide
Post Operations, if GI cause, Chemotherapy, Migraines
Domperidone
It can increase gastric emptying
Use in acute cases e.g for Parkinsons Disease medication
ADRs of D2 antagonists?
Dystonia
Galactorrhoea
Gynacomastia (increased prolactin)
What are the stages of vomiting?
Stimulation of the Vomiting Centre - Area Postrema
Warning Signs - lightheaded, fast breathing, feel hot/sweaty, pale
Glottis closes, Soft Palate raises, pyloric sphincter contracts
Diaphragm and abdominal muscles contract, Cardia Relaxes
What is metoclopramide?
Pharmacokinetics?
D2 antagonist
Oral, IM, IV
Half life of 4 hours
What is Domperidone?
Pharmacokinetics?
D2 antagonist
Oral, Rectal
Doesn’t cross BBB
Extensive 1st Pass Metabolism
How do 5HT antagonists work?
When used?
They work on the area postrema and periphery
They prevent vagal stimulation
Post Op
Chemotherapy
ADRs of 5HT antagonists?
Headaches
Constipation
Flushing
Example of a 5HT antagonist
Ondansteron
How do Histamine antagonists work?
When used?
Example?
Acute Cases e.g. MI
Cyclozine
How do ACh antagonists work?
When used?
Use in travel sickness
Short Half Life
Take 30 mins to take effect
ADRs of Histamine Antagonists?
Drowsiness
Long QT
ADRs of ACh antagonists?
Can become tolerant
Can cause systemic anti-muscarinic effects
Constipation
Bradycardia
What drugs do you use to treat constipation?
Bulk Forming Laxatives
Osmotically Active
Stool Softeners
Stimulants
How do you remember the 4 Constipation Drugs?
BOSS
Which treatments do you use if stool is found to be hard
Bulk Forming Stool Softener (Faecal Softeners)
What laxative should you use if there is soft stool?
Stimulants
What lifestyle recommendations would you make to someone with constipation?
Fibre Five a Day Fluid Alter Medication Exercise
What conditions can cause constipation?
Pregnancy
Parkinsons
Diabetes
Dehydration
Which Drug do you not use if dehydrated?
Bulk Forming Agents - ispagula
Bulk Forming Agents - MoA?
Insoluble vegetable fibre, not absorbed, distends the intestine, stretch receptors causing peristalsis
It also draws H20 into the bowel, to distend as well
Bulk Forming Agents - When?
In pregnancy - it is safe!
Takes a few days to work and bring bowel function back to normal
Bulk Forming Agents - ADRs?
Flatulence
Bulk Forming Agents - Example
Ispagula
Bulk Forming Agents - Contraindications
Obstruction
Dehydration
Ulceration
Faecal Softeners - MoA and Example
Stay in the bowel, lubricate and soften stool
Glycerol
Arachnis Oil
Faecal Softeners - When use?
If cannot tolerate fibre Very Safe Haemorrhoids Adhesions Anal Fissures
Faecal Softeners - Contraindicated
In Obstruction
Faecal Softeners - Why not very good?
Not always effective
Normally suppository
Osmotically Active Laxatives - MoA?
Mg or Na Salts draw water into the bowel, distends the bowel causing peristalsis
Osmotically Active Laxatives - When use?
Instant relief needed
Before Surgery
Before Colonoscopy
Osmotically Active Laxatives - PK
Examples?
When use?
Very Potent
Fast Acting
Lactulose - liver failure
Macrogols - helps dehydration
Osmotically Active Laxatives - ADRs
Can cause obstruction
Stimulant Laxatives - MoA
Irritate the bowel mucosa, stimulates peristalsis and H2O to go into the bowel
Stimulant Laxatives - Examples?
Senna
Castor Oil
Stimulant Laxatives - When Use?
Overnight - takes 6/8 hours
Rapid Treatment
Stimulant Laxatives - Contraindicated
Not Long Term - melanosis coli
Hypokalaemia
Stimulant Laxatives - ADRs
Obstruction
Cramps
Atony
Hypokalaemia
How do you treat diarrhoea?
Drug treatments treat the symptoms not the cause If can: Treat underlying cause Lifestyle Advice - no caffeine Manage fluids and electrolytes
What drug classes would you treat diarrhoea with?
Anti-motility - opioids
Bulk Forming Agents
Bile Acid Sequestants
Pancreatic Enzymes
Anti-Motility Drugs - MoA?
Examples?
Act on Opioid receptors on the bowel to reduce movement
Codeine, Imodium
Anti-Motility Drugs - Containdicated
IBD - Causes Toxic Megacolon
Anti-Motility Drugs - Positives?
Increase Anal Tone
Reduce Reflex to Defaecate
Anti-Motility Drugs - When use?
Chronic Diarrhoea
Bulk Forming Agents, why use in diarrhoea?
Creates a more formed stool
When do you use Bulk Forming Agents?
IBS
Ileostomy
Diverticular Disease
When would you use a bile acid sequesterant?
In Crohns Disease
If Bile Salt Induced
