Lecture 15 and 16 Flashcards
What is meant by the term emetic?
drugs that induce vomiting
What is meant by the term anti-emetic?
drugs that prevent vomiting
What is meant by the term anti-diarroeals?
drugs that stop diarrhea
What is meant by the term laxative?
drugs that promote voluminous stools
What is meant by the term pro-kinetics?
drugs that promote gut motility
What is meant by the term anti-ulcers?
drugs that make GI ulcers better
What is the main function of the CTZ?
The chemo-receptor trigger zone (CTZ) is driven by histamine and some other neurotransmitters. It deliberately remains outside of the brain itself which is very good if you happen to have digested a toxin that could kill you and doesn’t cross the blood brain barrier.
What is the difference between vomiting and regurgitation?
Vomiting = an active process Regurgitation = a passive process
Provide examples of species where vomiting is well developed and species that are not able to vomit:
Well developed = people, dogs, cats
Poorly developed = horses, ruminants, rodents, guinea pigs and rabbits
Provide an example of where vomiting may be a useful reflex:
Ingestion of a toxin e.g. snail pellets
Provide an example of a home remedy oral emetics?
Note these are all unreliable:
- 3% hydrogen peroxide
- hypertonic saline
- syrup of Ipecac
- SODA CRYSTALS - MPEC
Provide an example of a 100% efficacious emetic for dogs?
Apomorphine
What form does apomorphine come in and how can it be given?
- comes as very crumbly small tablets. Add to syringe dissolve in water for injection IV or SC or instill underneath the eyelid (conjunctival sac)
Can apomorphine be used for cats?
No
What is the scheduling of apomorphine?
Not an S8 (so S4)
Provide an example of an emetic that could be used in cats and briefly explain the mechanism of action of it:
Xylazine induces emesis in most cats. alpha-2 agonist at the CTZ
Why would an anti-emetic be beneficial?
to prevent loss of water (dehydration), pain, loss of electrolytes, loss of nutrients etc.
What is an important consideration to rule out before using anti-emetics?
GIT obstruction
What is the most commonly used anti-emetic?
Metoclopramide
Briefly describe the effects of metaclopramide and how they occur:
- anti-emetic effect (central action) - the central action is dopamine (low dose) and 5HT3 (high dose) antagonist at the CTZ
- weak upper GI prokinetic effect (peripheral action)
- 5HT4 agonist and DA antagonist sensitizing the stomach to muscarinic stimulation - the neurotransmitter dopamine is capable of inhibiting ACh
- increased tone of lower esophageal sphincter
- increased force and frequency of antral contractions
- relaxes pyloric sphincter
- promotes duodenal and jejunal peristalsis
How can metaclopramide be given and what is the duration of action of the drug?
can be given pretty much anyway and has a short duration of action - approximately 6 hours (as a result it needs to be given regularly)
What is the function of the anti-emetic prochlorperazine?
blocks the CTZ via antidopaminergic and antihistaminergic effects
How does the of the anti-emetic ondansetron work?
blocks serotonin (5-HT3). It is often used to treat the vomiting side effects of antineoplastic chemotherapy
How does ondansetron come?
In the form of rapidly dissolving wafers
What is the effect of the anti-emetic maropitant?
highly efficacious neurokinin-1 blocker
How can the sting of maropitant be reduced?
refrigerate it to stop (or reduce the sting)
What else can maropitant be used for (other than just an anti-emetic)?
Can also be used as an anti-nausea medication.
What are the two main conflicting views on the use of anti-diarrhoeals?
Historical view: stop the diarrhoea, allows avoiding of dehydration and electrolyte loss
Modern: let it go to purge the system of any toxins, letting it go allows monitoring of response to therapy, ensure fluid therapy is maintained
What types of opoids are used in anti-diarrhoeals and how do they work?
- use opiods that do not cross the blood brain barrier
- increased water retention and increased transit time
What is the function of Kaolin clay?
a clay that non-specifically absorbs everything including many toxins
Why is activated charcoal referred to as the universal antidote?
It is heated to 900 degrees celcius and then washed with organic acids to dry it out. The surface is then left with several carbon moieties that will absorb several different compounds with varying affinities.
What is an important consideration when using activated charcoal?
do not use it with mineral oil or other drugs as the oil will coat the absorption sites and may bind up other drugs
Differentiate between the term laxative and cathartic:
Laxative = soft-formed stool
Cathartic (purgatives) = a more speedy evacuation
What is the function of emollient laxatives?
soften and lubricate the faecal mass
What is an example of an emollient laxative?
Paraffin oil - good indicator of lumen patency - not very good at actually clearing the obstructions (important not to allow aspiration as this causes lipid pneumonitis)
Docusate sodium - surfactant action on stool allowing fluid and fat to penetrate the faecal mass
How do bulk laxatives work?
These are hydrophillic compounds that cause colonic swelling and reflex peristalsis of softer stools
What is an example of a bulk laxative?
Bran and Psyllium (branded as metamucil)
Provide an example of where magnesium sulfate can be an effective laxative:
Magnesium sulfate: very commonly used in cases of equine sand colic (far more effective than the use of mineral oil)
Explain how lactulose works and provide an example of where it is a good solution:
Fermented in the LI to form osmotic volatile fatty acids (VFAs) acting as a colonic sink that draws alkaline compounds into it. It is therefore suitable for hepatic encephalopathy where there is an excess of ammonia
What is an enema?
an ejection of liquid through the anus to stimulate evacuation (e.g. surfactants and soapy water)
What is a prokinetic and how do they usually work?
something that stimulates GIT motility. Often accentuates the action of ACh and/or inhibits dopamine (an ACh inhibitor)
Provide an example of a prokinetic and briefly explain the mechanism of its action:
Metoclopramide - see the mechanism of action above
Cisapride - acts on 5HT4 receptor leading to release of ACh in the myenteric plexus. Only available from compounding pharmacies.
Provide an example of an antispasmotic and state it’s mechanism of action:
An antimuscarinic - example: hyoscine
What do antacids do?
neutralisers of excessive acid
What do anti-ulcers do?
treatement and prevention of stomach ulcers
Name the factors that can stimulate the production of gastric acid:
- gastrin (endocrine)
- ACh (neurocrine)
- Histamine (paracrine)
What factors reduce the production of gastric acid?
PGE2
How are hydrogen ions (acid) secreted into the stomach lumen?
parietal cell through a H+-K+-ATPase pump
How does the anti ulcer drug omeprazole work and why is it the most effective in it’s class?
Works as a protein pump inhibitor. It is a weak base that is very unstable in the acidic stomach. So it is formulated in enteric coated granules. It is absorbed in the SI
What is an example of an H2 antagonist?
Ranitidine
What is an example of a sucralfate, can this class of drugs be sued prophalactically treat stomach ulcers?
An example of these is Aluminium sucrose sulfate. It is activated by HCl to form a paste like complex which then binds to an ulcerated area. Therefore, requires an ulcer to work.
How does misprostol work and what it the efficacy of it?
Weak but it is commonly used for the prevention of NSAID-induced gastric ulceration
How efficacious are the anti-muscarinics?
not been proven to work well in vivo
How efficacious are the antacids (Mg(OH)2)?
very short duration of action, so they are pretty useless for veterinary applications.
