GI drugs 3

what changes does bismuth cause in the stool?

turns it dark in color, so it could be confused with melena

why would it be important to know if your patient has had bismuth before taking radiographs or any other sort of diagnostic imaging?

because it is opaque and will show up/act like a contrast material

what drug can be used as an antiemetic and an antidiarrheal?

5-HT serotonin antagonists

how does 5-HT serotonin antagonists help stop diarrhea?

blocks 5-HT receptors which in turn reduces GI secretions

how does sulfasalazine stop diarrhea?

decreases prostaglandins and inflammation in colon caused by bacteria that cleaves off mesalamine

what can be a side effect of sulfasamide?

dry eye

what is an adsorbent?

causes other molecules to stick to the surface

how do adsorbents work as an antidiarrhetic?

• keep enterotoxins/irritating substances from contacting the GI tract wall

• used to prevent poisons from being absorbed into the body

what are protectans?

form a physical barrier between lumen contents and lining the GI tract

what are commonly used adsorbents?

• bismuth subsalicylate

• activated charcoal

• ± kaolin products

how does activated charcoal act as an adsorbent?

adsorbs poison molecules and prevents them form coming into contact with GI wall and being absorbed

how do laxatives, cathartics, and purgatives work?

increase fluid content of feces making them softer to ease/promote defecation

what are the uses of laxatives, cathartics, and purgatives?

• treat chronic constipation

• facilitate passing trichobezoars (hairballs)

• ease of defecation after pelvic or perianal surgery

• ease passage of stool in animal with pelvic injuries

from least to most aggressive, list laxatives, cathartics, and purgatives.

• laxatives

• cathartics

• purgatives

what are the two types of laxatives?

1. emollient

2. bulk

for what should you use laxatives?

softening stool and hairballs

for what should you use cathartics and purgatives?

to evacuate the bowel

what are some emollient laxatives that we typically use?

• mineral oil

• white petroleum

• cod liver oil

what are some bulk laxatives that we typically use?

• bran

• psyllium

• methylcellulose

what are some laxatives that we typically use as suppositories?

• glycerin

• docusate sodium or dioctyl sulfosuccinate

what is mineral oil administered for?

colic in horses

what is white petroleum administered for?

• dog laxative

• hairball prevention/treatment

what is cod liver oil administered for?

hairball remedy

what is glycerin administered for?

animals with severe pelvic fractures or need to easily pass stool through pelvic or perineal area

what is docusate sodium or dioctyl sulfosuccinate administered for?

acts as wetting agent to break down surface tension that prevents water penetration into hard fecal matter and may stimulate colic secretions to add fluid

what are bulk laxatives?

hydrophilic colloids or indigestible plant fiber

what are bulk laxatives administered for?

to create an osmotic force that pulls water into lumen and retains it

what are the two categories of cathartics?

1. osmotic (saline) cathartics

2. irritant cathartics

what are osmotic cathartics and what do they do?

• they are hypertonic salts

• they stay in the lumen and produce strong osmotic forces that attracts and holds water in the lumen

what osmotic (saline) cathartics do we use?

• milk of magnesia (magnesium hydroxide)

• epsom salts (magnesium sulfate)

what are some issues that can occur if giving osmotic (saline) cathartics to a patient?

• severe dehydration if overdosed

• ions can be absorbed if they stay in the gut for too long which can cause imbalances of the + and - electrolytes

what are side effects of excessive magnesium absorption?

muscle weakness, CNS problems

what are side effects of excessive phosphate absorption?

calcium loss (hypocalcemia) which leads to hypocalcemic tetany

why should phosphate laxatives or enemas including soaps w/ high phosphate content in cats?

they’re especially prone to phosphate/calcium imbalances

what is lactulose and what is it used for?

• a poorly absorbed sugar osmotic cathartic

• used for chronic constipation and to control signs from liver disease and high blood ammonia called hepatic encephalopathy by changing pH of colon which allows the ammonia to be more ionized and hence not absorbed by colon

what irritant cathartics do we use?

• castor oil

• bisacodyl

how do irritant cathartics work?

by irritating the bowl which causes increased peristalsis, aggressive movements, and increased secretions that add to the fluid of the GI tract

when should you not use irritant cathartics?

• in suspected obstructions or impacted feces

• in animals exhibiting tenesmus from colonic straining or after rectal/anal surgery

what is the normal pH of stomach acid?

2-3 pH

what is the stomach lining protected by?

layer of mucus produced by gastric glands in the stomach

what is mucus composed of?

mucin

what ion is added to the mucus in the lining of the stomach to neutralize the acid?

bicarbonate ion

T/F - prostaglandins are in charge of reducing acid production, but increasing mucus produciton

true

which cells produce stomach acid?

parietal cells

which cells excrete pepsinogen?

chief cells

which cells produce the hormone gastrin?

G cells

what does gastrin do?

helps regulate hydrochloric acid production by the parietal cells

explain the physiology of how stomach acid is made.

the proton pump within a parietal cell allows for a H+ ion to be released in the stomach fluid which will allow it to combine with Cl- to produce HCl which will then flow out of the gastric pit and into the lumen of the stomach

which 3 receptors stimulate acid production and pumping on the parietal cell?

1. H2 (histamine type 2)

2. acetylcholine

3. gastrin

of the 3 receptors in parietal cells that stimulate acid production and pumping, which has the greatest impact on acid production?

histamine

where is histamine released from?

specialized cells in the stomach called enterochromaffin-like cells

explain the physiology of stomach acid secretion.

when the animal sees food, smells it, or thinks about it, the parasympathetic nervous system is activated and releases acetylcholine and increases HCl production

where is stomach neutralized and how?

• in the duodenum

• by secretion of pancreatic bicarbonate

which type of health issues can cause increased acidity of the stomach?

• diseases that increase histamine in the blood

• increased PNS activity

• blocking beneficial prostaglandins

• reflux bile salts from duodenum

• toxins form renal failure

T/F - anything that increase stomach acid or pepsin production high enough to overwhelm the protective mucus layer produces damage to stomach and proximal duodenum.

true

what are the 2 types of antacids?

1. systemic

2. non-systemic

what are systemic antacids?

they have been absorbed and shut off acid production by blocking receptors on parietal cells

what are non-systemic antacids?

directly neutralize the acid by chemically combining with it and turning it into a less acidic molecule

what are some examples of non-systemic antacids?

• tums ®

• rolaids ®

• mylanta ®

• maalox ®

• amphojel ®

• milk of magnesia

what are the main 3 electrolytes non-systemic antacids are composed of?

1. calcium

2. magnesium

3. aluminum

what are the side effects of calcium and aluminum in non-systemic antacids?

constipation

what are the side effects of magnesium in non-systemic antacids?

diarrhea

why should magnesium antacid products not be used in renal failure patients?

because it is excreted by kidneys

how do antacids change the stomach acid pH and how does that affect drug intake?

antacids create a more alkaline pH in the stomach liquid which means that acid drugs like aspirin will become more ionized, so they won’t be absorbed as well

what are the 2 types of systemic antacids?

1. H2 blockers

2. proton pump inhibitors

what are some examples of systemic antacids?

• H2 blockers: cimetidine, ranitidine, famotidine, nizatidine

• proton pump inhibitors: omeprazole, espmeprazole, pantoprazole

how do systemic antacids work?

they must be absorbed to be effective AND they must attach to and block the stimulatory effects on parietal cell receptors, OR must attach to the proton pump and prevent it from pumping hydrogen ions into the stomach lumen regardless of how much the parietal cell is being stimulated

how do H2 blockers systemic antacids work?

by blocking histamine’s access to thew H2 receptor on the parietal cell

how does cimetidine work as a H2 blocker systemic antacid?

inhibits hepatic enzymes responsible for metabolism of other drugs

what happens if cimetidine is used simultaneously with other drugs?

causes decreased metabolism and accumulation of:

• beta blocker cardia drugs

• theophylline bronchodilators

• diazepam

what are the routes for the 3 proton pump inhibitor systemic antacids?

1. omeprazole - PO

2. esomeptrazole - PO

3. pantoprazole - IV

how do proton inhibitor systemic antacids work?

by binding to the lumen side of the proton pump and inhibit H= pumping into lumen

T/F - human antacids can be used for horses, however, it can’t be crushed or chewed because it needs to be degraded by stomach acid.

true

why do you have to be careful when giving equine gastrogard ® to race/performance horses?

some places/competitions don’t allow the administration of equine gastrogard ® within 24hrs

what are the 2 types of antiulcer drugs?

1. synthetic prostaglandin

2. sucralfate

what drug do we commonly use as a synthetic prostaglandin antiulcer drug?

misoprostol (cytotec ®)

what changes does misoprostol cause to the stomach?

• increase mucus production

• decrease acid production

• increases rate of cell turnover so ulcers/injury heal quicker

what is misoprostol used for as an antiulcer drug?

• used to prevent ulcer formation in dogs on aspirin therapy

• treatment for already formed ulcers

• stimulate GI tract and pregnant uterus to contract

how does sucralfate work as an antiulcer drug?

• creates a sticky paste that binds to ulcer site when exposed to acid and thus provides a physical barrier between the ulcer and the stomach acid

• stimulates local production of prostaglandins which aids in protection and healing of ulcer

why should you avoid simultaneous use of sucralfate with antacids?

because sucralfate needs an acid environment to be activated