GI

Question 1

Apomorphine
- How does it work?
- Which species should it NOT be used in?

Answer 1

GI - Emetic
- Dopamine agonist at the emetic center/CTZ
- Dissolve in WFI for IV or SC
- OR directly under eyelid
- Do NOT use in cats

Question 2

Xylazine (not as a sedative)
- How does it work?
- Use in what species?

Answer 2

GI - Emetic
- Alpha 2 agnostic at the CTZ
- Induces emesis in cats

Question 3

Metoclopramide (“Maxolon”)
- 2 effects

Answer 3

GI - Anti-emetic & Pro-kinetic

• (1)anti-emetic effect (central action) - Dopamine (low doses) and 5-HT2 (high dose) antagonist at the CTZ
• (2)weak upper GI prokinetic effect (peripheral action)
  >5-HT4 (serotonin) agonist and DA antagonist which stimulates release of ACh (rest and digest) and sensitises stomach to muscarinic stimulation - the neurotransmitter dopamine is capable of inhibiting ACh
  > increased tone of lower oesophageal sphincter
  > increased force and frequency of antral contractions
  > relaxes pyloric sphincter
  > promotes duodenal and jejunal peristalsis

Question 4

Prochlorperazine (“Stemetil”)
- How does it work?

Answer 4

GI - Anti-emetic
- Blocks CTZ via antidopaminergic and antihistaminergic effects

Question 5

Ondansetron
- How does it work?

Answer 5

GI - Anti-emetic
- Blocks serotitonin (5-HT3) - blocking the serotonin-mediated emetic stimuli & lots of 5-HT in GIT e.g. (gastroenteritis, inflammatory bowel disease (IBD), pancreatitis) –> peripheral serotonin release  central stimulation

Question 6

Maropitant (“Cerenia”)
- How does it work?

Answer 6

GI - Anti-emetic
- Neurokinin-1 blocker - NK-1 receptor is located in many places (central, peripheral) and has an array of actions including, but not limited to, vomiting
- Far more powerful than metoclopramide

Question 7

Kaloin (“Scourban”)
- What does it do?

Answer 7

GI - Anti-diarrhoeals
- clay that absorbs most things! including toxins

Question 8

Loperamide (“Imodium”)
- What does it do?

Answer 8

GI - Anti-diarrhoeals - opioid that doesn’t cross BBB
- Increased segmental tone & decreased propulsive contraction
- increased water retention and increased transit time

Question 9

Diphenoxylate (“Lomotil”)
- What does it do?

Answer 9

GI - Anti-diarrhoeals - opioid that doesn’t cross BBB
- Increased segmental tone & decreased propulsive contraction
- increased water retention and increased transit time

Question 10

Activated charcoal
- What does it do?
- Be careful bcs?

Answer 10

GI Anti-diarrhoeals
- Absorbs several different compounds with varying affinities
- Be careful with use with:
Mineral oil (eg paraffin oil) - wo;; coat the absorption sites of charcoal
Some other drugs - may bind and reduce efficacy

Question 11

Paraffin oil (mineral oil) (“Catlax”)
- What does it do?
- Indicator of what?

Answer 11

GI - Emollient laxative - soften and lubricate
- Indicator of GIT lumen patency Eg. sand colic

Question 12

Docusate sodium (“Coloxyl”)
- What does it do?

Answer 12

GI - Emollient laxative - soften and lubricate
- Surfactant action on stool - allows fluid and fat to penetrate the fecal mass
- breaking down fatty barriers - to better allow the water to penetrate the stool

Question 13

Psyllium (“Metamucil”)
- What does it do?

Answer 13

GI - Bulk laxative
- Hydrophilic compounds causing colonic swelling and reflex peristalsis of softer stools

Question 14

Magnesium sulphate (“Epson salts”)
- What does it do?
- Commonly used for what?

Answer 14

GI - Osmotic cathartic - draws fluid into GI tract
- Used for equine sand colic

Question 15

Lactulose (“Duphalac”)
- What does it do?
- Also helpful for what?

Answer 15

GI - Osmotic cathartic - draws fluid into GI tract
- Fermented in the large intestine by colonic bacteria, producing osmotic volatile fatty acids (VFAs) –> These VFAs lower colonic pH, making the colon more acidic.
- This acidity makes lactulose act as a “colonic acid sink”.
- Ammonia (NH₃), which is toxic and can cross the blood-brain barrier, is protonated by H⁺ from VFAs and converted into ammonium (NH₄⁺).
- NH₄⁺ is ionized and less readily absorbed, so it is excreted in feces instead of accumulating in the bloodstream.
- Therefore, lactulose is useful in hepatic encephalopathy—a condition where liver dysfunction causes ammonia buildup, leading to neurological signs.
- By trapping ammonia in the gut, lactulose helps reduce systemic ammonia levels and protect the brain.

Question 16

Cisapride
- How does it work?

Answer 16

GI - Pro-kinetic - promote gastric motility
- Acts at the 5-hydroxytryptamine (5-HT4) receptor causing increased release of ACh from the myenteric plexus

(decreased gut motility is a common problem in exotic animal medicine!)

Question 17

Hysocine/Scolamine (“Buscopan”)
- What does it do?
- Side effects
- Do not use when?

Answer 17

GI - Antispasmodic - antimuscarinic
- Reduces abdominal pain that is associated with GIT cramping/spasming
- Side effect: ileus (GIT complete shut down causing constipation etc), urine retention, tachycardia etc
- Do NOT use in infectious diarrhoea (e.g. salmonella) –> prevents clearance

Question 18

Omeprazole (“Losec”- tablets, “Gastrozol” - paste for horses)
- Treatment and/or prevention?
- How does it work?

Answer 18

GI - Anti-ulcer - Treatment and prevention of stomach ulcers
- Proton pump inhibitor

Question 19

Pantoprazole
- Treatment and/or prevention?
- How does it work?

Answer 19

GI - Anti-ulcer - Treatment and prevention of stomach ulcers
- Proton pump inhibitor

Question 20

Ranitidine
- Treatment and/or prevention?
- How does it work?

Answer 20

GI - Anti-ulcer - Treatment and prevention of stomach ulcers
- H2 antagnoist - histamine H₂ receptor antagonist (also called an H₂ blocker). It works by blocking H₂ receptors on parietal cells in the stomach lining, which reduces gastric acid secretion

Question 21

Sucralfate
- Treatment and/or prevention?
- How does it work?

Answer 21

GI - Anti-ulcer - ONLY a Treatment of stomach ulcers! (NOT a preventative!
- Activated by HCl to divide into aluminium hydroxide and sucrose octasulfate. The sucrose octasulfate forms a negatively-charged paste-like complex which electrostatically binds to the positively-charged ulcerated area.
- Therefore, requires an acidic environment AND an ulcer to work
- Requires an acidic environment to work
- Creates a barrier

Question 22

Antacids (Mg(OH)2 (Milk of magnesia), Al(OH)3, bicarb etc)
- What do they do?
- Disadvantage?

Answer 22

GI - Unimportant anti-ulcer - Neutralizers of excessive acid
- Lack in vivo efficacy and very short DOA

Question 23

How is vomiting triggered?

Answer 23

• Ach drives the response to various insults in organs
• Signals go to the brain to induce vomiting
  –> Vestibular apparatus - Histamine Eg. motion sickness
  –> Higher centers (cerebrum) Eg. thinking, seeing, smelling something
  –> CTZ (chemoreceptor trigger zone) Eg. drugs, endotoxemia (parts of gram neg bacteria)

Question 24

Laxative meaning
VS
Cathartic (purgatives) meaning

Beware of what with these kinds of drugs?

Answer 24

Laxative = soft forming stool
Cathartic (purgative) = more fluidy excavation

Beware of dehydration
= constipation due to lack of fluid in faeces
= can cause absorption of fluid from other places in GI tract - causing further dehydration

Question 25

What stimulates stomach acid secretion? What reduces stomach acid secretion? What do they all act on? - how does this work?

Answer 25

- Stimulated by: gastrin (endocrine), Ach (neurocrine), histamine (paracrine) and others ---> ALL ACT ON PARIETAL CELLS - Reduced by: PGE2 ---> ACT ON PARIETAL CELLS Parietal cells use a H⁺/K⁺-ATPase pump (proton pump) in their apical membrane to actively secrete hydrogen ions (H⁺) into the stomach lumen in exchange for potassium ions (K⁺).

Question 26

Using your knowledge of the physiology of acid secretion in the stomach, discuss why the proton pump inhibitors are the strongest medications for the treatment of gastric ulceration.

Answer 26

There are various stimuli that all result in acid being secreted into the stomach e.g. neurocrine (acetylcholine), paracrine (histamine) and endocrine (gastrin). Proton pump inhibitors are the most effective anti-ulcer medications because they will stop the release of acid into the stomach irrespective of the initiating cause. All other anti-ulcer medications are limited to more specific causes of acid secretion in the stomach.