GIT drugs Flashcards
1
Q
What is the autonomic nervous system?
A
comprised of both PSNS & SNS - GIT movement and secretions are controlled by interaction between nervous system and endocrine hormones
2
Q
What does the PSNS include?
A
cranial nerves of the brainstem and peripheral nerves from spinal cord
3
Q
What is the neurotransmitter of the PSNS?
A
Acetylcholine - ACh
4
Q
What does the vagus nerve do?
A
carries nerve impulses to and from organs in chest and abdomen
5
Q
What does activation of the PSNS (or drugs that mimic ACh) do?
A
- increase digestive secretions (HCl)
- increase blood flow to GIT
- increase GIT smooth muscle tone and motility
> increased digestion and absorption by PSNS activation = rest and digest
6
Q
What does the SNS include?
A
nerves emerge from thoracic and lumbar spinal cord
7
Q
What is the neurotransmitter of the SNS?
A
norepinephrine/epinephrine
8
Q
What does activation of the SNS (or drugs that mimic it) do?
A
- decrease blood flow to GIT
- decrease GIT motility
- decrease GIT secretions
> decreased digestion & absorption = fight or flight
9
Q
Where is the emetic center?
A
group of neurons in the medulla of the brainstem
10
Q
Where do the nerve pathways from the emetic center connect to?
A
- chemoreceptor trigger zone (CRTZ)
- cerebral cortex
- peripheral receptors in:
> pharynx
> GIT
> Urinary system
> Heart
11
Q
What does the emetic center do?
A
coordinates the smooth muscle contraction and ANS function that produces nausea, abdominal and stomach contractions
12
Q
What are the receptors of the emetic center?
A
alpha, serotonin, histamine, neurokinin, acetylcholine,
& dopamine
13
Q
What can stimulate the emetic center to produce the vomiting reflex?
A
- drugs/chemicals that directly affect emetic center (apomorphine)
- stimulation of the inner ear (motion sickness, infection)
- stimulation of the brain by emotions (pain, fear, brain swelling)
- distention/irritation of the pharynx, stomach, SI, kidney, uterus
- metabolic conditions (uremia, endotoxemia)
- direct stimulation of CRTZ
14
Q
What is the CRTZ?
A
- chemoreceptor trigger zone
- specialized area of receptors adjacent to emetic center that monitor blood and CSF for chemicals that can stimulate emesis > send signals to emetic center when stimulated
15
Q
What are the receptors in the CRTZ?
A
same as emetic center + opioids
16
Q
Why does the CRTZ detect toxic substances better than the emetic center?
A
this area of the brain is not protected by blood brain barrier
17
Q
How do receptors in the CRTZ vary amongst species?
A
- numbers and types vary
- dogs have more dopamine and histamine than cats
- cats have more alpha
18
Q
How does histamine affect vomiting and the GIT?
A
histamine mediated signals sent from inner ear vestibular apparatus
> H1 receptors on CRTZ = vomiting
> H2 receptors on gastric parietal cells = stimulate production of HCl
19
Q
What do bacterial toxins affect?
A
toxins produced by some bacteria (E.coli, Salmonella) can cause increased secretions in the GIT = diarrhea and dehydration
certain toxins will also trigger vomiting
20
Q
When do we use emetics?
A
- if an animal was not fasted before sx
- known ingestion of poisonous substances (1-2hrs of ingestion with liquid toxins) (solid poisons can stay in stomach for up to 4 hrs)
> may not want to in all poison cases
21
Q
When should emetics not be used?
A
- horses, rabbits, GP’s, other rodents that can’t vomit
- extremely depressed or sedated animals
- ingested corrosive agents or petroleum products
- seizing or likely to seizure
- GI issues - bloat, torsion, esophageal damage
22
Q
What are the 2 different groups of emetics?
A
- centrally acting emetics (CRTZ)
> apomorphine
> a2 agonists - locally acting emetics
> hydrogen peroxide
23
Q
What are some a2 agonists that we can use for emetics?
A
Xylazine - 90% of cats will vomit (30% dogs)
Dexmedetomidine - more likely in cats but less than xylazine
24
Q
What are the risks with using hydrogen peroxide?
A
can be irritating = gastritis if don’t vomit
risk of aspirating froth
(1-2ml/kg no more than 45ml)
25
What is the risk of using salt?
danger of salt toxicosis if don't vomit - DO NOT USE
26
What are the risks with emesis?
aspiration pneumonia
hematemesis
corrosion of esophagus
27
What are some other options if emesis isn't one?
- gastric lavage
- activated charcoal
- surgery (?)
28
How do antiemetics work?
decrease emesis by either blocking:
- receptors in CRTZ
- receptors on emetic center
- peripheral receptors that send signals to the brain
29
How do phenothiazines work as an anti-emetic?
block dopamine and histamine receptors in the CRTZ
(lower dose than used for sedation, used for motion sickness too)
Acepromazine or chlorpromazine
30
How do antihistamines work as an anti-emetic?
blocks histamine in the CRTZ (motion sickness or vomitng), can cause sedation
Dimenhydrinate (Gravol)
Diphenhydramine (Benadryl)
31
What is ondansetron? When is it commonly used?
it is a serotonin receptor antagonist (serotonin receptors are found on vagal nerve terminals and the CRTZ), mostly used during chemotherapy as anti-emetic
32
How do neurokinin antagonists work?
Block NK-1 receptors in CRTZ
Maropitant Citrate (Cerenia)
33
What do prokinetic drugs do?
- increase gastric contraction and peristalsis of SI
- increase muscle tone in lower esophagus
- relaxes pyloric sphincter
> all decrease emesis by pushing stomach contents forward and out of stomach quicker
34
What is metaclopramide? What is it commonly used for?
prokinetic drug, used as antiemetic for parvovirus enteritis, chemo, motility disorders
35
How do anticholinergics work as antiemetics?
block parasympathetic stimulation, decrease GIT motility, many effects in addition to antiemetic
36
How do anatacids and antiulcer drugs work?
control gastric acid production - parietal cells in stomach produce acid (HCl) which is stimulated by histamine (greatest effect), gastrin, & acetylcholine
37
What is gastrin?
hormone released from G cells in lining of stomach and duodenum in response to stretching of stomach from food/liquid and PSNS stimulation, gastrin stimulates release of histamine
38
How is acetylcholine released, what does it do?
anything that stimulates PSNS stimulates release of acetylcholine, increases acid production
39
How is mucus produced?
locally produced prostaglandins in the stomach stimulate mucus production and inhibit acid production
40
What happens if the mucous producing prostaglandins are blocked?
decreased mucous production & increased acid production = gastric ulcers
41
What are antacids and antiulcer meds used for?
treat and prevent:
- gastric/duodenal ulcers
- esophagitis
- gastric reflux
42
What do H2 receptor antagonists do? What are 3 common ones?
block H2 receptors on parietal cells in the stomach to decrease HCl release
Cimetidine (Tagamet)
Ranitidine (Zantac)
Famotidine (Pepcid)
43
What can H2 receptor antagonists alter?
mainly cimetidine - inhibit certain hepatic enzymes > alter metabolism of some cardiac drugs & anticonvulsant drugs
44
How do acid (proton) pump inhibitors work?
bind to surface of parietal cells and inhibits pump that transports hydrogen ions into the stomach = less acid production
45
What is omeprazole? What is it mostly used for?
it is an acid pump inhibitor, used mostly in horses to treat and prevent gastric ulcers in horses
46
What is sucralfate? How does it work?
gastromucosal protectant - forms sticky paste that binds to the ulcer site to protect from acid or bile salts
47
What is misoprostol? What does it do?
synthetic prostaglandin type drug - increases mucous production, decreases acid production, facilitates healing of ulcer
48
Who should not be given misoprostol?
Pregnant animals - can cause uterine contractions
49
What can cause diarrhea?
- malabsorption/digestion
- hypersecretion of fluids into intestinal lumen
- increased permeability of intestinal mucosa
- hypermotility - to remove enterotoxins
50
How do antidiarrheal medications work?
- modify intestinal motility
- block hypersecretions
- absorb & protect
51
How do antidiarrheals that modify intestinal motility decrease motility?
- decreasing peristaltic contractions
- increasing segmental contractions in SI
- have anti-secretory effect
52
How do narcotic antidiarrheals work?
combine with mu receptors to decrease gut motility, decrease intestinal secretions, enhance intestinal absorption
Loperamide (Imodium)
53
What is given with narcotic antidiarrheals?
low dose atropine to discourage potential ingestion of high dose (would cause analgesic or sedative properties) - produce dry mouth and dilated pupils
54
What are adsorbents?
drug molecules that cause other molecules to bind to their outer surfaces - toxic, irritating, disease causing molecules adhere and can't be absorbed
55
What are protectants?
cover intestinal wall to form a protective coating
56
What is bismuth subsalicylate?
Pepto bismol - bismuth has adsorbent properties (caution in cats) & changes stool color - black
57
What are kaolin and pectin?
Kaopectate - coats and protects intestine - kaolin has adsorbent properties
58
What is activated charcoal?
Toxiban/Charcodote - absorbs enterotoxins and ingested toxins
59
What are laxatives/cathartics?
used to increase fluid content of the feces - cathartics are laxatives with strong/harsh effects
60
How do hyperosmotic laxatives work?
contains magnesium or phosphate anions that are very poorly absorbed from GI tract, anions hold water in the tract = softened stool, stimulate stretch receptors to enhance peristalsis
61
How do hypertonic salts work?
poorly absorbed so they create a strong osmotic force to draw water into bowel lumen, magnesium can also cause the release of a hormone that will increase peristalsis
Magnesium - epsom salts
Phosphate - fleet enema
62
What are some cautions with hypertonic salts?
if absorbed from giving too much or sitting in bowel too long can cause:
- electrolytes imbalances (muscle weakness and CNS alterations)
- dehydration
absorption of phosphate can cause hypocalcemia
do not use these in cats (most susceptible to electrolytes imbalances)
63
What is lactulose?
- hypertonic sugar
- used for chronic constipation
- can reduce ammonia levels in patients with hepatic disease
64
What are bulk laxatives?
ingestible plant fiber that creates an osmotic force to pull water into the gut - softens stool, increases size and stimulates peristalsis
Vetasyl
bran, canned pumpkin
Psyllium - metamucil
65
What are lubricants?
typically oils or petrolatum products that soften fecal mass - treat constipation and fecal impaction
66
What are the risks associated with using mineral oil by itself?
risk of aspiration - tasteless = no stimulation of swallow reflex
may be absorbed from an inflamed gut
67
What are glycerin suppositories used for?
soften stool to help pass through colon and rectum in patients with pelvic fractures, or pelvis with narrowed diameter
68
How do surfactants/stool softeners work?
change surface tension of fecal matter allowing water to penetrate and soften stool
docusate sodium succinate (DSS) - Colace
BloatEze
Antibloat
69
How do irritants work?
irritate the bowel = increased peristaltic motility and increased secretion
Castor oil
Bisacodyl - Dulcolax, senokot
70
When should we not use irritants and why?
Strong stimulant activity so do not use in animals with obstructed bowels, impacted feces, or tenesmus, or rectal/anal sx
71
What are prokinetics/stimulants?
increase motility of gut = enhances gastric emptying
Metoclopramide - treat gastric reflux, delayed gastric emptying
72
What are digestive enzymes used for?
treat exocrine pancreatic insufficiency - contain lipase, amylas and protease
Viokace
73
What are prebiotics?
- non digestible dietary supplement
- usually carbs
- ferment in gut
- decrease pH
- selectively increases growth of good bacteria in the gut
FOS (fructo-oligosaccharide)
MOS (mono-oligosaccharide)
74
What are probiotics?
dietary supplement of live micro-organisms
- modify intestinal bacteria to increase good gut flora
Enterococcus
Lactobacillus sp.
75
What is rumenatoric?
drugs used to stimulate contractions in a hypomotile or atonic rumen
Rumex
Oxamin
76
How do antibloat medications work?
reducing number of microorganisms that produce gas, or break up bubbles formed in frothy bloat - decreasing surface tension causes small bubbles to rupture and form much larger gas pockets that can be eructated from rumen
77
What are some antibloat medications?
Docusate Sodium succinate - decreases viscosity of rumen contents allowing foam to dissipate (Bloat Lax, Bloat eze)
Mineral oil - decreases viscosity of rumen contents and decreases stability of bubbles
78
How do ionophores work?
anticoccidial drug but also balances rumen microflora so less foamy slime produced - have controlled released concentration capsules for pasture use, toxic to horses
Monensin
Rumensin
79
How do poloxalene work?
reduces surface tension of rumen fluid and prevents froth formation
