Autonomic Nervous System Sympathetic Fight or Flight Parasympathetic EAT TURKEY amp SLEEP IT OFF Control Mechanisms of the GI Tract One control mechanism of the GI tract is the autonomic nervous system parasympathetic and sympathetic branches ID: 753625
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Slide1
Chapter 11
Gastrointestinal DrugsSlide2Slide3Slide4Slide5
Autonomic Nervous System
Sympathetic = “Fight or Flight”
Parasympathetic =
EAT TURKEY & SLEEP IT OFFSlide6
Control Mechanisms of the GI Tract
One control mechanism of the GI tract is the autonomic nervous system (parasympathetic and sympathetic branches)
Parasympathetic stimulation increases intestinal motility, increases GI secretions, and relaxes sphincters
Cholinergic drugs simulate these actions
Anticholinergic
drugs inhibit these actions
Sympathetic stimulation decreases intestinal motility, decreases GI secretions, and inhibits the action of sphincters
Sympathetic nerves simulate these actionsSlide7
Gastrointestinal Disorders
Among the most common complains in veterinary medicine
Underlying causes include:
Infectious sources, dietary excess, adverse drug effects, systemic disease
These disorders result in clinical signs such as:
Diarrhea, constipation, vomiting, bloat, ulcer development,
(generally associated with pain)Slide8
Drugs Affecting the GI Tract
Antisialogues
Drugs that decrease salivary flow
Used to limit the flow of excess saliva, which often occurs secondary to anesthetic drug use
Examples include
anticholinergics
such as
glycopyrrolate
and
atropineThese drugs can also affect peristalsis because they are also used to treat vomiting, diarrhea, and excess gastric secretionSlide9
Glycopyrrolate
(
Robinul
) and AtropineSlide10
Antidiarrheals
Antidiarrheals
are drugs
that decrease peristalsis, thereby allowing fluid absorption from the intestinal contents
Examples:
Anticholinergics
Protectants
/adsorbents
Opiate-related agents
ProbioticsMetronidazoleSlide11
Antidiarrheals
Anticholinergics
are used to treat
tenemus
and vomiting
Examples:
Atropine
Aminopentamide
IsopropamidePropanthelineMethscopolamineSide effects include dry mucous membranes, urine retention, tachycardia, and constipationSlide12
Antidiarrheals
Protectants
& Adsorbents
Protectants
coat
inflamed intestinal mucosa with a protective layer
Adsorbents
bind
bacteria and/or digestive enzymes and/or toxins to protect intestinal mucosa from damaging effectsExamples:Bismuth subsalicylate (bismuth + aspirin-like product)Kaolin/pectinActivated charcoalSide effects include constipationSlide13
Antidiarrheals
Opiate-related agents
Narcotic analgesics control
diarrhea by decreasing both intestinal secretions and the flow of feces and increasing segmental contractions
Examples:
Diphenoxylate
Loperamide
Paregoric
Side effects include CNS depression,
ileus, urine retention, bloat, and constipationSlide14
Antidiarrheals
Probiotics
Probiotics
seed the GI tract with beneficial bacteria; use is based on the theory that some forms of diarrhea are caused by disruption of the normal bacterial flora of the GI tract
Must be refrigerated to maintain the viability of the bacteria
Examples:
Plain yogurt with active cultures
Variety of trade-name productsSlide15
ProbioticsSlide16Slide17
Antidiarrheals
Metronidazole
A theory regarding the development of diarrhea is that anaerobic bacteria may increase due to disruption of normal GI flora
One way to treat this is to use an antibiotic effective against anaerobic bacteria
Metronidazole
is an example of an antibiotic used to treat diarrheaSlide18
MetronidazoleSlide19
Laxatives
A laxative loosens the bowel contents and encourages evacuation of stool
Laxatives help animals evacuate without excessive straining; treat chronic constipation from
nondietary
causes and movable intestinal blockages; and evacuate the GI tract before surgery, radiography, or diagnostic procedures
Cathartics
are harsher laxatives;
purgatives
are harsh catharticsSlide20
Laxatives
Types of Laxatives include:
Osmotic
Stimulant
Bulk-forming
EmollimentsSlide21
Laxatives
Osmotic
Pull water into the colon and increase water content in the feces, thereby increasing bulk and stimulating peristalsis
Are salts or saline product that may cause electrolyte imbalances if absorbed systemically
Examples include:
lactulose
, sodium phosphate with sodium
biphosphate
, magnesium sulfate, magnesium hydroxideSlide22
Laxatives
Stimulant
Increase
peristalsis by chemically irritating sensory nerve endings in the intestinal mucosa
Many are absorbed systemically and cause a variety of side effects
Examples include
bisacodyl
, phenolphthalein, and castor oilSlide23
Laxatives
Bulk-forming
Substances that absorb water into the intestine, increase fecal bulk, and stimulate peristalsis, resulting in large, soft stool production (which tends to look normal)
Are not systemically absorbed, so side effects are rare
Examples include
psyllium
hydrophilic
mucilloid
,
polycarbophil,and branSlide24
Laxatives
Emollients
Can be stool softeners (reduce stool surface tension and reduce water absorption through the colon), lubricants (facilitate the passage of fecal material, increasing water retention in stool), or fecal wetting agents (detergent-like drugs that permit easier penetration and mixing of fats and fluid with the fecal mass
)
Examples include
docusate
sodium,
docusate
calcium,
docusate potassium, and petroleum productsSlide25Slide26
Antiemetics
Antiemetics
Drugs that control vomiting that help alleviate discomfort and help control electrolyte balance
Most are given
parenterally
, as the patient may vomit the medication before it can be absorbed through the GI tract
Examples:
Phenothiazine
derivativesAntihistaminesAnticholinergicsProcainamide derivativesSerotonin receptor antagonistsSlide27
Antiemetics
Vomiting has many causes including:
Viral and bacterial infections, dietary indiscretion, food intolerance, surgery, pain, or other drugs
The vomiting center of the brain have many inputs that tell it to activate including:
Equilibrium changes in the ear, responses due to pain or fear, intracranial pressure changes,
vagus
nerve stimulation in the GI tract, and activity in the chemoreceptor trigger zoneSlide28
Antiemetics
Phenothiazine
derivatives
Inhibit dopamine in the chemoreceptor trigger zone, thus decreasing the stimulation to vomit
Side effects include hypotension and sedation
Examples:
Acepromazine
Chlorpromazine
ProchlorperazinePerphenazineSlide29
Antiemetics
Antihistamines
Controls vomiting when the vomiting is due to motion sickness, vaccine reactions, or inner ear problems
Work by blocking input from the vestibular system to the CRTZ
A side effect is sedation
Examples:
Trimethobenzamide
Dimenhydrinate
DiphenhydramineSlide30
Antiemetics
Anticholinergics
Block acetylcholine peripherally, which decreases intestinal motility and secretions
May decrease gastric emptying (which may increase the tendency to vomit)
Side effects include dry mouth, constipation, urinary retention, and tachycardia
Examples:
Aminopentamide
Atropine
PropanthelineSlide31
Antiemetics
Procainamide
derivatives
Work centrally by blocking the CRTZ and peripherally by speeding gastric emptying, strengthening cardiac sphincter tone, and increasing the force of gastric contractions
Should not be used in animals with GI obstructions, GI perforation, or GI hemorrhage
An example used in veterinary medicine is
metoclopramideSlide32
Antiemetics
Serotonin
receptor antagonists
Work selectively on 5-HT
3
receptors, which are located peripherally and centrally
Work on the theory that some chemicals cause vomiting because they increase serotonin release from small intestinal cells
Examples:
Ondansetron
DolasetronSlide33
Maropitant
(
Cerenia
®)Slide34
Antiemetics
Neurokinin
receptor antagonists
Work on NK1 receptors located in the center of the brain
Work by inhibiting substance P, the key neurotransmitter involved in vomiting
Maropitant
citrate
(
Cerenia®)Used to prevent acute vomiting and motion sicknessSide effects include:Pain at the injection site, hypersalivation, and diarrheaSlide35
Emetics
Emetics
Drugs that induce vomiting
Used in the treatment of poisoning and drug overdose
Vomiting should
not
be induced if caustic substances have been ingested
Always check with poison control prior to inducing vomiting
Activated charcoal is given if emesis is contraindicated (it absorbs many chemicals and drugs in the upper GI tract)Slide36
Emetics
Can be centrally acting (working on the CRTZ) or peripherally acting (working on receptors locally
)
Centrally acting
Apomorphine
Xylazine
Peripherally acting
Ipecac syrup
Home remediesSlide37
Inducing Emesis
Apomorphine
XylazineSlide38
Antiulcer Drugs
Antiulcer drugs
Help prevent the formation of ulcers
Categories include
Antacids
Histamine-2 receptor antagonists
Mucosal protective drugs
Prostaglandin analogs
Proton pump inhibitorsSlide39
Antiulcer Drugs
Antacids
Promote ulcer healing by neutralizing
HCl
and reducing pepsin activity
Interact with other drugs
By adsorption or binding the other drugs
By increasing stomach pH
By increasing urinary pH
May be systemic or nonsystemicExamples:Systemic: sodium bicarbonate, calcium carbonateNonsystemic: magnesium hydroxide, aluminum/magnesium hydroxide, aluminum hydroxideSlide40
Antiulcer Drugs
Histamine-2
receptor antagonists
Prevent acid reflux by competitively blocking the H
2
receptors of the parietal cells in the stomach, thus reducing gastric acid secretion
Examples:
Cimetidine
(
Tagament®)Ranitidine (Zantac®)Famotidine (Pepcid®)Slide41
Antiulcer Drugs
Mucosal protective drugs
Combine with protein to form an adherent substance that covers the ulcer and protects it from stomach acid and pepsin
An example is
sucralfateSlide42
Antiulcer Drugs
Prostaglandin
analogs
Suppress gastric secretions and increase mucus production in the GI tract
An example is
misoprostol
, which is usually given to animals taking
NSAIDs
Proton pump inhibitors
Bind irreversibly to the H+-K+-ATPase enzyme on the surface of parietal cells of the stomach; this inhibits hydrogen ion transport into the stomach so that it cannot secrete HClExamples:OmeprazoleLansoprazoleSlide43Slide44
Antifoaming Agents
Reduce or prevent the formation of foam
Used in ruminants, whose rumens are subject to acute frothy bloat
Make this foam less stable, breaking it up to promote gas release through belching
Administered as solutions by stomach tube directly into the
forestomach
Examples include
poloxalene
and polymerized methyl siliconeSlide45
Motility Enhancing
Prokinetic
agents
Increase the motility of parts of the GI tract to enhance movement of material through
it
Types of
prokinetic
agents
are:
parasympathomimeticsdopaminergic antagonistsserotonergic agentsSlide46
Prokinetic
Agents
Parasympathomimetic
agents include
Acetylcholinesterase
inhibitors, which compete with
ACh
for
acetylcholinesterase, resulting in increased intestinal tone and salivationAn example is neostigmineCholinergics, which make a precursor to acetylcholineAn example is dexpanthenolSlide47
Prokinetic
Agents
Dopaminergic
agents stimulate
gastroesophageal
sphincter, stomach, and intestinal motility by sensitizing tissues to the action of the neurotransmitter
ACh
Examples include
metoclopramide and domeridoneSerotonergic agents stimulate motility of the gastroesophageal sphincter, stomach, small intestine, and colonAn example is cisaprideSlide48
Enzyme Supplements
Pancreatic
enzymes must be supplemented in the diet when the pancreas is not functioning properly (as in pancreatic exocrine insufficiency)
Pancrealipase
contains primarily lipase, but also contains amylase and protease
Can be irritating to the skin on contact and to nasal passages upon inhalationSlide49
Appetite-Stimulating Drugs
Serotonin antagonist antihistamines
Promote appetite by inhibition at the
serotoninergic
receptors which control satiety
Side effects include sedation and dry mouth
Benzodiazepines
Effective appetite stimulants in cats but not dogs
Side effects include sedation and ataxia
Tetracyclic antidepressantsStimulate appetite by antagonizing alpha2-receptorsSide effects include sedation, vocalizationSlide50
Appetite Stimulating Drugs
Glucocorticoids
Stimulate steroid-induced euphoria which stimulates appetite
Side effects include
polydipsia
,
polyuria
, dull
haircoat
, weight gain, and behavioral changesAnabolic steroidsStimulate hematopoiesis, appetite, and weight gainSide effects include hepatotoxicity, masculinization, and early closure of growth plate in young animalsSlide51
Appetite Stimulating Drugs
Progestins
Used to stimulate appetite and promote weight gain in anorectic cats and dogs
Side effects include behavioral changes,
endometritis
, and mammary
enlargementSlide52
Appetite Suppression
Dirlotapide
(
Slentrol
®)
Drug for management of obesity in dogs
Side effects include vomiting, diarrhea, lethargy, and anorexia