Gastrointestinal Flashcards
What can cause physiochemical injury to the GI tract lining?
Some NSAIDs, caustics
What can cause hyperacidity in the GI tract?
Histamine release from MCTs
Cholinergic stimulation
Glucocorticoid therapy
What causes impaired cytoprotection in the GI tract?
NSAID therpay
What causes inflmmation in the GI tract?
Ulcerative colitis
What is understood about the role of stress and infection in causing gastric ulcers?
Once believed that stress prevented ulcers from being removed. This turned out to not be the case. Doesn’t play a role in animals that we know of
Pig and horses are a potential exception.If you had to say one species that is predisposed to stress induced ulcers, it would be the horse
In man, helicobacter is a major predisposing factor to gastric ulcers. Doesn’t play a role in animals
Dogs and cats can culture positive for helicobacter in the ulcer, but normal dogs and cats also culture positive for helicobacter in the stomach
Infectious: granulomatous colitis of Boxers (histiocytic ulcerative colitis)
What is the site of action of H2 receptor antagonists?
H2 receptors
What is the site of action and mechanism of PPIs?
H+/K+ ATPase
Blocks the generation of the hydrogen ion such that is not produced regardless of stimuli from receptors
What is the site of action and mechanism of misoprostol?
PG receptors
A synthetic PGE analog, it replaces the PG decreased by NSAID therapy to reestablish the cytoprotective mucus
What is the site of action and mechanism of sucralfate?
Binds to the surface of the ulcer
Forms a coating over the ulcer, acts locally, prefers an acid environment for optimal effect
What is an oral and injectable PPI?
Oral: Omeprazole
Injectable: Pantoprazole
Why is sodium bicarb no longer used as a routine oral antacid?
Rebound hyperacidity
Why do common human OTC antacids contain a combination of aluminum hydroxide and magnesium hydroxide rather than only one or the other?
Aluminum hydroxide can be constipating so it is often combined with MgOH which acts as a laxative
Why may oral antacid therapy for abomasal ulcers be of use in cattle while oral antacids are frowned upon for use in small animals and horses?
In cattle, the rumen meters out the compound producing long-term antacid effects. In SA and horses, you have to give po q 2hrs for it to be effective- that’s just not feasible
What are the effects of cimetidine as an enzyme inhibitor and a prokinetic?
Potent P450 enzyme inhibitor; drug interactions
No effect on GI motility
What are the effects of ranitidine as an enzyme inhibitor and a prokinetic?
Mild P450 inhibition; less prone to drug interactions
Prokinetic GI activity
What are the effects of famotidine as an enzyme inhibitor and a prokinetic?
Not a P450 inhibitor
No prokinetic GI activity
What rule of thumb is used regarding the timing of sucralfate administration relative to when other oral drugs or food is given?
Give at least 2 hours before or 2 hours after other oral medication or food
What is the merit of using a sucralfate suspension versus its use as a tablet?
Tablet may not dissolve and disperse adequately in small animals
Historically to treat/prevent GI ulcers in small animals it was common to place patients simultaneously on an H2 blocker and a proton pump inhibitor. What was the basis for this simultaneous use, what evidence supports it, and is it still warranted?
Recent research indicated acid suppression occurred in the dog as fast with proton pump inhibitors (PPI) as with H2 blockers. While some clinicians still prefer to begin with an H2 blocker, the majority now go straight to PPIs
How can you manage NSAID-induced ulcers?
Misoprostol is most effective
Omeparzole is also very useful
H2 blockers least effective
How can you manage steroid-induced ulcers?
H2 blockers
Omeprazole is also very useful
Misoprostol is least effective for gastric ulcers
What receptors involved in vomiting are in the chemo-receptor trigger zone?
5-HT3 D2 M NK1 δ α2
What receptors involved in vomiting are in the solitary tract nucleus?
5-HT3
D2
M
H1
What receptors involved in vomiting are in the stomach/SI?
5-HT3
D2
What receptors involved in vomiting are in the BBB between the inner ear and cerebellum?
H1
M
What receptors involved in vomiting are between higher centers and emetic center/medulla?
M
What species are not capable of vomiting?
Rodents Rabbits Most birds Horses Ruminants
Why should you not cause emesis in small animals after ingestion of caustics (strong acids or bases), petroleum distillates, or oils? What should be done instead?
Oils that are thrown up can have high risk of aspiration
Caustic agents will irritate and damage esophagus on the way back up
Do a gastric lavage instead
How do 3% hydrogen peroxide and apomorphine cause vomiting in the dog? What concerns exist about their use in cats?
Apomorphine works on chemo-receptor trigger zone which goes to the emetic center in the medulla and causes your pet to up chuck
Cats have had esophagitis and gastritis from H2O2 administration
How do xylazine and dexmedetomidine cause vomiting in the cat? How does route of administration affect their efficacy as emetics?
As a blood emetic, it causes vomiting by working on the chemo-receptor trigger zone which goes to emetic center
Unfortunately, the IV route is less likely to cause emesis in cats
The drug meclizine typically is only useful for what type of vomiting and on what receptor does it work?
Motion sickness
Works on H1 receptors
Which antiemetics have both central and peripheral antiemetic effects?
Metoclopramide
Serotonin 5-HT3 receptor antagonists (Ondansetron and dolasetron)
Extra-pyramidal side-effects can occur with an overdose of what two types of antiemetics? What mechanism of action do they share? What signs are associated with such side-effects?
Metoclopramide and Phenothiazine tranquilizers (acepromazine)
These are both central antidopaminergic antiemetics
Cause alpha 1 blockade –> vasodilation, risk of hypotension and hypothermia
PCV is lowered by ace
Do not use metoclopramide if GI obstruction exists because it is a prokinetic and you risk rupture
What antiemetics work on H1 receptors?
Diphenhydramine
Dimenhydronate
Meclizine
Promethazine