Lower GI pharmacology Flashcards
What is the proper name for vomiting
emesis
HOW do toxins cause vomitin
Can affect visceral afferents or directly affect chemoreceptors
Different anti-emetics
- H1- receptor antagonists
- Anti-muscarinic agents
- Dopamine antagonists
- 5-hydroxytryptamine antagonists
- Nabilone
- Steroids
What are H1 receptor antagonists used for
- Motion sickness
- Have anti-muscarinic actions
What are side effects of anti muscarinic agents
Are anti-muscarinic drugs so:
-Blurred vision, dry mouth, constipation, urinal tension
What are the uses of anti-muscarinic agents
Motion sickness and irritation of stomach
What do H1 receptors act on
Vestibular nuclei
What are the actions of dopamine antagonists and what are they effective against
Acts in chemoreceptor trigger zone but has unwanted CNS effects (drug induced Parkinson’s)
-effective against anticancer drug-induced emesis
What is the action of 5-hydroxytryptamine antagonists and what is it effective against
Blocks 5-HT at 5-HT3 receptors in gut and CNS
-Effective against anti-cancer drugs
WHen are steroids commonly used
IN patients with cancer
How do adhesive enterotoxigenic bacteria cause diarrhoea
Adhere to brush border, increase cAMP leading to Cl- and Na+ secretion followed by water
How does cholera cause diarrhoea
CFTR is a Cl- specific channel
- Cholera infects
- CHolera toxin chemically modifies G protein
- Activates adenylyl cyclase
- Rise in cAMP which activates cl- channel and efflux of cl- from cell and that leads to removal of water from body
What drugs may diarrhoea be secondary to
Antibiotics
ORlistat (anti obesity drug) (is a pancreatic lipase inhibitor and so will cause fatty diarrhoea as fat is not being digested) (steatorrhea)
Misoprostol
PPIs
Which antibiotic may lead to pseudomembranous colitis
Clindamycin (c.difficil causes)
What is the first step of action for those with diarrhoea
Oral rehydration therapy (solution of electrolytes to replace electrolytes lost in diarrhoea)
- ->Must be isotonic
- ->glucose allows transport of Na via a symporter
How does oral rehydration therapy work
Amount of glucose is the right osmolarity. Glucose and sodium piggy back same transporter, sodium flows into cell with glucose and that is then followed by water
When are antibiotics used for diarrhoea?
Are of little value. If a microbiologist identifies a causative bacteria then appropriate antibiotics may be used.
Are probiotics appropriate for diarrhoea>
Can be recommended for elderly and children because it may reduce the duration of infection
how else can diarrhoea be treated
Antimotility agents: opioids such as codeine and loperamide (Imodium)
How do anti motility agents help with diarrhoea
Reduce tone and peristaltic movements of GI muscle by inhibiting the release of acetylcholine
Mode of action of anti motility agents
- Normally, depolarisation activates Ca2+ channel and calcium moves into cell. Act causes muscle to contract and that causes GI muscles to contract
- loperamide activates opioid receptor. This switches off AC enzyme and reduces levels of cAMP and so activates K+ channels and K+ moves out. Causes hyper polarisation and so stops Ca2+ entry and stops release of ACh
Benefits and drawbacks of anti motility agents
Provides symptomatic relied but does not shorten the course of the infection and could potentially increase the time of infection
Side effect of codeine
COnstipation
What side effects do some tricyclic antidepressants have
COnstipation
