GI pharmacology Flashcards
Functions the GI system performs
Takes food and fluid into the body
Absorbs nutrients and fluid
Excretes waste products
Ruminant Stomach chambers
Reticulum
Rumen
Omasum
Abomasum (the “true” stomach)
Horses, rabbits, and some rodents have developed … (part of GI system)
a very large colon, which helps them to digest plant material,
Two stomachs of birds
proventriculus (stomach)
ventriculus (gizzard)
Colon
*removes water from the material, *forms certain vitamins in hind-gut fermenters (a part of the colon in rabbits and horses),
*stores waste products
salivary glands
begin enzymatic digestion by producing enzymes that break down starch into simpler carbohydrates.
Pancreatic enzymes (general process)
Go to the duodenum to break down fats, carbohydrates, and proteins,
sodium bicarbonate from the pancreas
neutralizes hydrochloric acid from the stomach.
Bile salts,
Produced in the liver
delivered to the duodenum
aid in digestion by emulsifying fats.
Bile
Stored in the gallbladder
Gall bladder is absent in some animals (e.g., horses and rats).
Structures of GI tract
Dpends on the species
the mouth, teeth, tongue,
salivary glands,
esophagus and outpocketings of the esophagus (i.e., crop, reticulum, rumen, and omasum),
stomach,
liver,
pancreas,
duodenum,
jejunum,
ileum,
cecum,
colon,
rectum,
anus.
Three basic regulation systems of GI system:
The autonomic nervous system (ANS).
Gastrointestinal hormones
specialized cells of the GI tract
specialized cells of the GI tract
Gastric parietal cells use H2 receptors to attach histamines which increases the release of hydrochloric acid in the stomach.
Gastrointestinal hormones
Gastrin, secretin, and cholecystokinin
exert control over many functions such as gastric secretion, emptying of the gallbladder, and gastric emptying.
The autonomic nervous system regulation of GI system (big picture)
- Stimulation of the parasympathetic portion
- Stimulation of the sympathetic branch
- Stimulation of various intrinsic receptors in the GI tract, such as the myenteric plexus (stretch receptor), also may increase peristaltic activity.
Cool fact - Bonus -Some physiologists consider the intrinsic receptors (myenteric plexus and Meissner’s plexus) to be a third portion of the ANS called the enteric nervous system (Ganong, 2003).
Stimulation of the parasympathetic system in GI regulation (3)
Increases intestinal motility and tone,
increases intestinal secretions,
stimulates relaxation of sphincters.
Stimulation of the sympathetic branch in GI regulation
Decreases intestinal motility and tone,
decreases intestinal secretions,
inhibits sphincters.
The myenteric plexus (stretch receptor) may
increase peristaltic activity in the GI system
chemoreceptor trigger zone (CRTZ)
An area in the brain that activates the vomiting center when stimulated by toxic substances in the blood.
vomiting center
An area in the medulla that may be stimulated by the chemoreceptor trigger zone, the cerebrum, or peripheral receptors to induce vomiting.
Emetic contraindications
1) are comatose or are having a seizure,
(2) have depressed pharyngeal reflexes,
(3) are in shock or have dyspnea,
(4) bloat or esophageal damage,
(5) have ingested strong acid, alkali, or other caustic substances.
Emetic
Agents used to induce vomiting.
Animals that don’t usually vomit
rabbits, some rodents, and horses
Apomorphine (GI system)
A morphine derivative that stimulates dopamine receptors in the CRTZ and acts as an emetic.
this drug is poorly absorbed after oral administration and is therefore usually administered parenterally or topically in the conjunctival sac
Xylazine
Not classified as an emetic,
the label indicates that it induces vomiting within 3 to 5 minutes.
Some clinicians consider xylazine to be the agent of choice for inducing vomiting in cats.
Yohimbine or atipamezole can be used to reverse the emetic effects.
Hydrogen Peroxide for vomiting
can be used orally to induce vomiting.
Caused by irritant effect on the oropharynx and stomach lining
The dosage is 1 mL/lb (1 teaspoon (5 mL) per 5 pounds) of body weight.
Not to exceed 45 ml
Can be repeated once
Don’t need to remember all this but …
The oropharynx includes the following tissues:
The middle part of the throat behind the mouth.
The back one third of the tongue.
The soft palate (the back of the roof of the mouth), including the uvula.
The side and back walls of the throat.
The tonsils.
Antiemetics
prevent or control vomiting by blocking receptors in the CRTZ, emetic center, and peripheral receptors.
these drugs do not necessarily correct the underlying cause of the vomiting
Usually are given parenterally because vomiting precludes use of the oral route.
Phenothiazine-derivative antiemetics
block dopamine receptors in the CRTZ and possibly
inhibit the vomiting center.
Commonly used in vet med
very useful in preventing motion sickness in dogs and cats but may be less effective against irritant emetics
(Example ace)
Acepromazine for GI
has antiemetic effects. It is a phenothiazine.
Metoclopramide (GI pharmacology)
Central and peripheral antiemetic activities.
Centrally -blocks dopamine receptors in the CRTZ, whereas Peripherally - increases gastric contraction, speeds gastric emptying, increases peristalsis of the small intestine, and causes relaxation of the pyloric sphincter.
Less important -Has a short half-life and may have to be administered often or in a continuous drip in severe cases of vomiting
Note -* Atropine and the opioid analgesics may antagonize the actions of metoclopramide.
Serotonin Receptor (5-HT3) Antagonists (GI pharmacology)
Serotonin receptors are found on vagal nerve terminals and in the CRTZ
Causes antiemetic activity.
Example- Ondansetron (Zofran)
NK-1 antagonists (GI pharmacology)
block the binding of substance P (a neurotransmitter peptide found in the emetic center) to NK-1 receptors in the CRTZ.
Example- Cerenia
hematemesis
Vomiting of blood (the vomitus often resembles coffee grounds).
melena
Dark or black stools that result from blood staining. Bleeding has occurred in the anterior part of the gastrointestinal tract.
Gastric ulcers reasons and signs
Occur for various reasons, including stress, metabolic disease, gastric hyperacidity, and drug therapy (e.g., corticosteroids or nonsteroidal antiinflammatory agents) (Hall, 2001).
Anorexia, hematemesis, pain, and melena are common signs of gastric ulcer.
Classes of drugs for gastric ulcers
(1) H2 receptor antagonists,
(2) proton pump inhibitors
(3) antacids
(4) gastromucosal protectants
(5) prostaglandin E1 analogues.
Parietal cells
responsible for gastric acid secretion,
H2 Receptor Antagonists
H2 receptor antagonists reduce the release of hydrochloric acid, thus decreasing irritation of the eroded mucosa and promoting healing
H2 receptors are activated by histamine.
Example -Ranitidine (zantac), famotidine (5 times as strong as ranitidine),
Proton Pump Inhibitors
Bind irreversibly at the secretory surface of the parietal cell to the enzyme Na-K-ATPase.
When bound the enzyme is inactivated and the cell is unable to secrete acid until a new enzyme is synthesized
Example- Omeprazole
Na-K-ATPase
This enzyme is responsible for “pumping” hydrogen ions into the stomach against a concentration gradient.
(H ions help modify PH)
Antacids
*nonabsorbable salts of aluminium, calcium, or magnesium.
*Example- Aluminum/magnesium hydroxide (Maalox, Mylanta)
Less important - *In ruminants are used to treat rumen acidosis (rumen overload syndrome) and as a laxative.
*Antacids also may be used in patients with renal failure to reduce hyperphosphatemia
Antacid contradictions
Generally, do not give oral antacids within 1 to 2 hours of other oral medications because of their ability to decrease the absorption of drugs
Magnesium-containing antacids are contraindicated in animals with renal disease.
Narcotic Analgesic for GI
(1) increase segmental contractions,
(2) decrease intestinal secretions
(3) enhance intestinal absorption.
Their use in cats and horses is controversial because of their tendency to cause CNS stimulation.
Anticholinergics and antispasmodics GI
The coating action protects inflamed mucosa from further irritation.
Their adsorbent activity binds bacteria or their toxins to protect against their harmful effects
Examples - Kaolin and pectin, Bismuth subsalicylate, activated charcoal
Caution should be used when using salicylates in cats.
Saline/Hyperosmotic Agents GI
Contain magnesium or phosphate anions that are very poorly absorbed from the GI tract.
These anions hold water in the tract.
Increased water in the GI tract then softens the stool and stimulates stretch receptors
Example- lactulose
Bulk-producing agents GI
Often indigestible plant materials
Act by absorbing water and swelling to increase the bulk of intestinal contents
Surfactants
Stool softeners
Reduce surface tension so water penetrate GI contents, May increase intestinal secretions.
Irritants GI pharmacology
Irritate the gut wall, causing stimulation of GI smooth muscle and increased peristalsis.
seldom used in veterinary medicine.
motilin
A hormone secreted by cells in the duodenal mucosa that causes contraction of intestinal smooth muscle.
Prokinetic/stimulant drugs
Increase the motility of a part or parts of the GI tract and by doing this enhance the transit of material through the tract. Several classes of drugs can fall in this category
Dopaminergic antagonists (GI pharmacology)
Is a prokinetic drug
Stimulate motility of the gastroesophageal sphincter, stomach, and small intestine.
Examples include metoclopramide and domperidone
Motilin-Like Drugs
Erythromycin treats bacterial and mycoplasmal infections Stimulate GI motility by mimicking the effect of the hormone motilin
Uses may include increasing lower esophageal sphincter pressure, accelerating gastric emptying
Acetylcholinesterase Inhibitors (GI system)
Increase the amount of acetylcholine available to bind smooth muscle receptors.
Treats rumen atony, enhances gastric emptying, stimulate peristalsis, empty the bladder of large animals,
Not important for this card aids in the diagnosis of myasthenia gravis
Pancrelipase
A product that contains pancreatic enzymes that aid in the digestion of fats, proteins, and carbohydrates.
Mix with the animal’s food, which is allowed to stand for 15 to 20 minutes before feeding.
used to treat exocrine pancreatic insufficiency (EPI) in which maldigestion and malabsorption of nutrients occurs.
Metronidazole
a synthetic antibacterial and antiprotozoal agent.
prohibited from use in food-producing animals by the FDA.
Adverse Side Effects: include CNS signs (disoriented, head tilt, and seizures), anorexia, hepatotoxicity, neutropenia, vomiting, and diarrhea.
Should not be given to debilitated, pregnant, or nursing animals.
Antiinflammatory agents (GI)
used in the treatment of inflammatory bowel disease include prednisone, azathioprine, sulfasalazine, and olsalazine.
IBD
Increased numbers of lymphocytes, macrophages, plasma cells, or eosinophils in the intestinal wall characterize these diseases. Treatment often involves the use of hypoallergenic diets and antiinflammatory agents.
Antifoaming agents
Used for the treatment of frothy bloat in ruminants by decreasing the surface tension of foam in the rumen.
Probiotics
Commercial probiotic products typically contain strains of Lactobacillus species, Bifidobacterium species, and Enterococcus species.
One billion to 10 billion colony-forming units (CFUs) per day is a recommended dose
Prebiotics
nondigestable food ingredients that are beneficial to the bacterial population. Synbiotics contain both prebiotics and probiotics.
Appetite Stimulants
(Types and cat info)
Cats who do not eat adequately for a period of time may develop a “fatty liver” syndrome that can be life threatening.
Examples-
* Diazepamran - transient appetite stimulation when given intravenously
* Cyproheptadine—oral antihistamine primarily for cats
* Mirtazapine (Remeron)—oral use in dogs and cats
* Capromorelin (Entyce)—oral use in dogs only
Sucralfate
a disaccharide that that forms a pastelike substance in the stomach that binds to the surfaces of gastric ulcers.
Tylosin
- a macrolide antibiotic that is sometimes used to treat chronic colitis in animals.
- should not be used in horses as it may cause severe diarrhea.
Doxirobe
Placed in the periodontal pocket after dental cleansing with the use of a cannula.
Upon contact with the aqueous environment, the product coagulates and releases doxycycline for several weeks.
A serotonergic prokinetic that
Stimulates motility of the proximal and distal GI tract
Cisapride
Can reduce vomiting associated with megaesophagus
Processed in the liver
Misoprostol
Decrease stomach acid
A synthetic prostaglandin E1 analogue that directly inhibits the parietal cell from secreting hydrogen ions into the stomach.
It also increases the production of mucus and bicarbonate.
Because it’s a prostaglandin it will increase uterine contractions and can cause premature birth or abortion and therefore should not be used in pregnant animals
