Chapter 11 Gastrointestinal Drugs - PowerPoint Presentation

Slide1

Chapter 11

Gastrointestinal DrugsSlide2
Slide3
Slide4
Slide5

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

ProbioticsSlide16
Slide17

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 productsSlide25
Slide26

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:OmeprazoleLansoprazoleSlide43
Slide44

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