GI Drugs Flashcards
When is antiemetic therapy indicated, give examples?
When vomiting is debilitating or associated with a chronic condition (e.g. pancreatits) where the cause of the vomiting has been determined
To prevent excessive fluid or electrolyte loss. Eg. after eating a toxic substance (as long as are sure the substance has been cleared)
What schools of thought are there that are against antiemetic therapy?
When there is an obstruction (increasing gut motility may lead to increased risk of gut perforation)
Infections - may result in longer times for the infection to clear
Toxic substance ingestion - emesis is there to remove toxins.
Outline the pathways associated with vomiting.
Which is the key integrator of this system?
The nucleus tractus solitarius is the integrator of the vomiting pathway
Which receptors are associated with which system?
NTS - neurokinin 1 (NK1)
CRTZ - D2, M1, 5HT3, H1 & H2
Vestibular - M1 (also linked to CRZT in dogs)
Vomiting Centre - a2, 5HT1a
Peripheral - D2, M2, 5HT3, Motilin
What are the classes of antiemetic drugs?
NK1 antagonists
Metaclopramide
Phenothiazines
Antihistamines
5HT3 antagonists
Anticholinergics
What is the drug that affects NK1 receptors?
What species is it effective in?
What is it indicated for?
Maropitant
Dogs
Acute gastroenteritis, motion sickness, cytotoxicity induced vomiting (labelled for the last one but not neccessarily that effective for it). It is useful against both peripheral and central causes of vomiting.
What should be taken into account when using Maropitant?
It is extremely effective so may mask underlying disease. Ensure correct diagnosis is repeat treatments are needed. Do not use if GI obstruction is suspected.
What is the mechanism of action of Metaclopramide?
D2 and 5HT3 antagonist => works on the CRTZ and peripheral receptors.
It also has a pro-cholinergic effect so increases gut motility.
How do phenothiazines work?
They antagonise:
- D2
- a1 & a2
- H1 & H2
- Muscarinic receptors
Therefore they work on all of the centres involved in vomiting apart from the NTS.
What are Phenothiazines indicated for? Is there anything that needs to be taken into account?
Any cause of vomiting.
They are not veterinary registered in the UK
What can antihistamines be used for?
Causes of vomiting in the CRTZ, only really effective in dogs. Particularly for motion sickness as the CRTZ has a link with the vestibular system.
Cats do not really suffer from motion sickness.
Where is the mechanism of action for 5HT3 antagonists and what are they often used for?
CRTZ and peripherally. They are generally used for cytotoxic drug induced emesis (e.g. cancer therapy).
What are the different anticholinergics?
Atropine
Butylscopolamine
Propantheline
Isopromide
What is the problem with anticholinergic anti emetics?
Although they act on the M1 receptors in the vestibular system they also act on peripheral M2 receptors which are involved in regulating gut motility, which can cause more problems.
What are the different classes of anti-ulcer drugs?
- Systemic antacids
- H2 receptor antagonists
- Sucralfate
- Misoprostol (synthetic PGE)
- Omeprazole (PPI)
Describe the advantages of systemic antacids.
Probably not that effective and need to be used frequently and given orally - poor compliance and not tolerated in vomiting patient. They only treat but DO NOT prevent ulceration. They are cheap.
Why are H2 antagonists considered anti-ulcer drugs rather than anti-emetic drugs?
They ONLY affect the stomach, rather than the CRTZ, which has H1 receptors.
What are some H2 receptor antagonists, which are available for veterinary use?
Cimetidine, ranitidine & famotidine. Only cimetidine is licenced.
What are the H2 antagonists useful for?
NSAID induced ulceration & ureamia for example.
What does the use of H2 antagonists depend on?
Cost, client conveinience and concurrent drug therapy.
Is sucralfate licenced for veterinary use?
No but it is very effective and very safe.
What is the main use for Misoprostol and why?
It is mainly used in prevention/treatment of gastric ulcers due to NSAID treatment or in treatment of NSAID toxicity as it is a synthetic PGE2.
NSAIDs deplete prostaglandins which are essential for proper gut and renal function.
What is the main safety concern when using Misoprostol?
It is the morning after pill so needs to be handled with extreme care for some owners.
Why is the rationale for using Omeprazole reduced?
What is it used for?
Cinetidine is now licenced so can also use this.
Ulcers/Oesophagitis that are refactory to other treatments. Or Ulcers associated with gastrinomas or MAST cell tumors.
What is the rationale for electrolyte solutions?
Enhance fluid absorption from the gut. They do no harm and give the owner something to do.
How can hypermotility be treated by drug therapy?
Use Opiods or anticholinergics. These will rarely be indicated as hypermotility is rare and diarrhoea either resolves itself or chronically will not respond to symptomatic treatment.
Are adsorbents and protectants useful?
Give an example of one of these, in what species is its use contraindicated?
No, may actually be worse. Gives owner something to do.
Bismuth salicylate - AVOID USE IN CATS
What about probiotics?
No proven efficacy in animals
Do no harm - better than using antibiotics for diarrhoea!! Gives owner something to do.
