Gi drugs

why is it important to know the stomach of the animals?

they affect the absorption and utilization of drugs

how is the gi tract function/controlled?

a balance interaction between the nervous system, hormone of the endocrine system and other locally release compounds

Effects of the parasympathetic system (acetylcholine neurotransmitter)

-improve blood flow to the gi tract

-increase gut tone and motility

-slows HR, constrict pupils

increase secretion in respiratory tree

Effects of sympathetic (epinephrine, norepinephrine)

-decrease blood flow to intestinal tract, motility, secretions

-increase HR, dilates pupils, opens respiratory aiway

-redirects blood away from nonessential areas

how do emetic drugs work?

stimulate receptors in which in turn activate the physiologic mechanism of vomiting

What two areas do emetic drugs work on?

-the vomiting reflex the emetic center

-the CRTZ

What is the emetic center?

A group of special neurons located in the medullary structure of the brainstem that produces the physiologic actions associated with the period just before vomiting and during the actual act of vomiting itself

what is the chemoreceptor Trigger Zone?

Adjacent to the emetic center is a specialized cluster of receptors that constantly monitor the blood and the cerebrospinal fluid for chemicals that can stimulate vomiting.

NOT protected by the BBB

what are the major receptors involved in emetic/antiemetic drugs?

-serotonin

-Dopamine

-Acetylcholine

-Norepineprine/epinephrine

-Histamine (H1)

-Substance P (NK-1)

How do emetic drugs work?

work by stimulating receptors which in turn activate the physiologic mechanisms of vomiting

5 mechanism that cause vomiting

-Drugs bind directly to receptors on emetic center and stimulate neurons

-Drugs bind directly to the CRTZ

-Nerve signals sent from distended or irritated pharynx, stomach, duodenum, small intestines, peritoneum, kidney, gallbladder, uterus

-Nerves of the inner ear/balance become overactive

-Higher centers of the brain or emotional signals in the brain send signals

receptors associated with CRTZ

Alpha

5-HT

H1

NK1

Opioids

DA

receptors associated with Vestibular apparatus (inner ear)

H1

Cholinergic

mechanism associated with higher cortical centers

fear

anxiety

emotional shock

emotional response to pain

receptors associated with the emetic center

5HT

Acetycholine

H1

DA

Alpha

NK1

structures that sent signals

GI

Peritoneum

Kidney

Uterus

Bladder

in what instances should you not induce vomiting

-Corrosive substances

-Volatile petroleum liquids

-Comatose, depressed, unconscious, or absence of gag reflex

-Anesthetized

-Convulsing or those exhibiting preictal signs

-Bloat, gastric torsion, esophageal damage

-Animals that do not vomit

What 2 things should you known before inducing vomiting?

-the timing of when the toxin was ingested

-when was the last time they have eaten

what are the two methods to induce vomiting

-centrally acting emetics

-locally acting emetics

how do centrally acting emetics work?

Act by stimulating the emetic center or the CRTZ

Opioid emetic agent more effective in dogs than cats

apomorphine

emetic agent more effective in cats than dogs. This drug is an alpha 2 agonist and is more commonly used as an injectable sedative.

xylazine

Neurokinin-1 (NK-1) receptor antagonist antiemetic drug introduced in 2006 for control of motion-induced vomiting

maropitant

how do locally acting emetics work?

Typically produce their effects by locally irritating the GI tract

Locally acting emetic agent recommended for use if a locally acting agent is needed. Produces gastritis especially in cats. Needs to be fresh

hydrogen peroxide

Antiemetic drugs

-phenothiazine tranquilizers

-Antihistamine antiemetics

-Anticholinergic

-Prokinetics

-Serotonin Antagonist

-Neurokinin 1 receptor antagonist

phenothiazine antiemetics (inhibit dopamine in CRTZ decreasing stimulation to vomit)

acepromazine

chlorpromazine

prochlorperazine

Phenothiazine antiemetic also used as a common veterinary tranquilizer

acepromazine

Antihistamine Antiemetics

-Dimenhydrinate

-Diphenhydramine

-Meclizine

These two human drugs attach to and block H1 receptors as their mechanism to decrease the effects of motion sickness.

dimenhydriante

diphenhydramine

prokinetics drugs as anti emetics

metoclopramide

cisapride

This prokinetic agent and antiemetic works by blocking dopamine (and probably serotonin) receptors on the CRTZ but also by increasing gastric and intestinal motility in the "normal" direction.

metoclopramide

This drug is still available as a human drug, unlike another member of this drug group that has been withdrawn from the human market and is only available by compounding.

metoclopramide

serotonin antagonist antiemetics

ondansetron

granisetron

dolasetron

Serotonin antagonist antiemetic used to control vomiting from cancer chemotherapy in dogs or pancreatitis in cats that is poorly controlled by other antiemetic agents

ondansetron

neurokinin 1 receptors antagonist

maropitant (cerenia)

How do antidiarrheal drugs work?

Drugs that change intestinal motility or reduce the secretions that contribute to diarrhea

why does diarrhea occur?

-Diarrhea is normally a protective mechanism that helps remove irritating or toxic substances from the intestinal tract

-the balance between fluid secretion from the body into the intestinal lumen and the fluid absorption from the intestinal lumen fluid into the body has been altered, resulting in more fluid being secreted into or remaining in the feces

4 general forms of diarrhea

-secretory

-exudative

-motility

-osmotic/malabsorption

2 types of contraction involved in intestinal motility

-segmental contractions, which are circular contractions around a small segment of intestine that mix the contents of the bowel,

-peristaltic contractions, which move in waves to propel the food along the tract

Antidiarrheal drug that modifies motility

Narcotics (diphenoxylate) (loperaminde)

These over-the-counter opioid anti diarrhea drugs work by increasing segmental contractions and reducing intestinal secretions

diphenoxylate

loperamide

antidiarrheal by blocking secretions

-bismuth subsalicylate

-ondansetron

-Sulfasalazine

This compound is broken down in the GI tract into a compound that coats the intestinal mucosa and another compound that is an aspirin-like antiflammatory drug

bismuth subsalicylate

This drugs is an adjunct antidiarrheal drug that is also an antiemetic. It works by blocking 5-HT3 receptors in the GI tract to reduce secretion of chloride ions and water

-ondansetron

-Dolasetron

-Granisetron

This drug is a sulfonamide antibiotic linked chemically to mesalamine (5-aminosalicylic acid), the latter compound being an anti-inflammatory compound cleaved from the drug molecule by colonic bacteria to treat inflammatory colitis.

sulfasalazine

adsorbent/protectants as antidiarrheals. MOA: coating inflamed intestinal mucosa by binding bacteria, digestive enzymes or toxins to protect.

-bismuth

-kaolin

-pectin

-liquid barium

-activated charcoal

This is the component of bismuth subsalicylate that is an absorbent

bismuth

This absorbent is not usually used to treat diarrhea but is used to decrease absorption of ingested poisons. Is sometimes referred to as the universal antidote

activated charcoal

how do laxative, cathartics, and purgative work?

increase the fluid content of the feces, making them softer and easing/promoting defecation

why are laxatives, cathartics, and purgative used?

-Control chronic constipation

-Facilitate passage of Trichobezoars

-Evacuate the colon for radiographs

-Ease the passage of stool for surgical patients

difference between laxatives and cathartics

laxative: soften

cathartics: purgatives

two categories of laxatives

-emollient

-Bulk

Emollient laxatives

-commonly used after anal surgery or pelvic fractures when passage of a firm stool may be painful.

-mineral oil, cod liver oil, white petrolatum, Glycerin, DSS

This emollient laxative is most commonly administered by stomach tube to horses to treat suspected impactions. A major risk of using this drug is aspiration because it has little taste.

mineral oil

these two emollient laxatives are common ingredients of dog and cat laxatives used to treat hairballs.

cod liver oil

white petrolatum

• Glycerin

• Docusate sodium succinate wetting agent

This emollient laxative is used as a suppository to ease the passage of stool through the colon or rectum of animals with pelvic fractures or compression of the diameter of the pelvic canal.

glycerin

This emollient laxative is a stool softener that acts by allowing water to penetrate hard stool. (surfactant)

docusate sodium succinate

how do bulk laxatives work?

-Osmotically pump water into the bowel lumen and retain water in feces

bulk laxatives (put water into bowel lumen and retain water in feces)

bran

psyllium

methylcellulose

metamucil

This osmotic cathartic is also used to decrease ammonia absorption from the GI tract in patients with hepatic encephalopathy.

lactulose

These two irritant laxatives work by stimulating peristalic activity and secretions into the bowel

castor oil, bisacodyl

how does damage to the stomach lining occur?

balance is disrupted in the safety mechanisms that contain highly acidic liquid

what protects the stomach from the acidity?

-parietal cells (pump H and Cl ions against) (histamine, acetylcholine, gastrin)

-chief cells (pepsinogen via acetycholine)

-mucous cells (mucin via prostaglandins)

how do antiacids/antiulcer drugs work?

-decrease acidity by binding to HCl-

or by decreasing production

systemic antiacids

-not used in vet med

-decrease production

nonsystemic antiacids

neutralize or coat

These four drugs are H2 antagonist antacids

cimetidine, ranitidine, famotidine, nizatidine

Of the H2 antagonist antacids, this is the one that most significantly inhibits hepatic enzymes by reducing biotransformation of other commonly used drugs and therefore requiring the veterinary technician check this drug's interaction with other drugs

-cimetidine

Acid pump/ proton pump inhibitor antacid.

omeprazole

Antiulcer drug that forms a sticky paste that covers the ulcer in proximal duaduem(combines with protein to form adherent substance covering ulcers, protects from stomach acid and pepsin)

sucralfate

Synthetic prostaglandins type E1 drug that mimics the beneficial effects of natural GI tract prostaglandins (antiacid)

misoprostol

Ruminatoric (prokenetic) that acts by blocking acetylcholinesterase destruction of the acetylcholine neurotransmitter, stimulate an atonic or flaccid rumen

neostigmine

ionophores

-A group of antimicrobial drugs

-The ability of these compounds to facilitate transport of selected ions (e.g., Na+, K+) across a cell membrane

Widely used ionophore in beef and dairy cattle to improve rumen health; is also used to reduce coccidiosis in livestock and poultry.

monensin

how do anti bloat meds work?

-Designed to reduce gas build up or facilitate the removal of gas from the rumen

-Reducing numbers of rumen microorganisms that produce the gas

-By breaking up the bubbles formed in the frothy bloat (DSS, poloxalene)

Stool softener also used to break up froth in frothy bloat (antibloat for rumen)

DSS, Dioctyl sodium succinate

why are antimicrobials sometimes used in Gi cases?

some can kill gram-positive bacteria, alters the natural flora of bacteria in the GI tract

Antimicrobials used in GI cases

-Tylosin

-Metronidazole

-Erythromycin

-Sulfasalazine

Macrolide antibiotic used to treat both respiratory and GI tract bacterial infections in cattle and swine, as well as selected types of chronic diarrhea in the dogs. Do not use it in horses

tylosin

Antibiotic developed initially to treat Giardia protozoa but has been found to also be effective in treating diarrhea of unknown origin in dogs and cats. Can cause neurologic side effects at higher doses or more prolonged use.

metronidazole

A macrolide antibiotic similar to tylosin that commonly causes cramping as a side effect but has also been used as a prokinetic agent to stimulate sluggish gastric emptying

erythromycin

whya are oral electrolytes replacements used?

Administered orally to help replace ions lost with diarrhea or vomiting

why are pancreatic enzyme supplements used?

-The pancreas fails to produce sufficient amounts of the following digestive enzymes

Pancreatic enzyme supplement for use in dogs with exocrine pancreatic insufficiency (EPI)

pancrealipase

why is using corticosteroids controversial?

the beneficial anti-inflammatory effect is offset by immunosuppression, increased gastric acid production, suppression of normal gastric protective and healing mechanisms, and increased risk of infection