Pharmocology

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Emetics

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drug that produces vomiting with the intent of removing an ingested toxic substance

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Centrally Acting Emetics

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Apomorphine and Xylazine

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Apomorphine

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Opioid that stimulates dopamine receptors in the CRTZ to produce emesis. High blood concentrations needed in order to not depress CNS

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Xylazine

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Used in cats. Sedative and anesthetic agent stimulates alpha 2 receptors in the CRTZ and the emetic center. Works in dogs but at a much lower rate

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Locally Acting Emetics

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typically produce their effect by irrating the GI tract, distending the stomach, and causing parasympathetic stimulation of the emetic center. Ipecac, hydrogen peroxide, warm table salt water, powdered mustard. Do not work consistently. Hydrogen peroxide can cause gastritis. Salt can cause salt toxicity or dehydration.

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Antiemetics

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Prevent or decrease vomiting

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Phenothiazine Tranquilizers

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Acepromazine, Chlorpromazine, and Prochlorperazine.

Block dopamine receptors in the CRTZ thereby reducing vomiting. Also have an antihistamine effect which helps prevent and control motion sickness in dogs. Some anticholingeric activity. Alpha adrenergic receptor antagonist activity blocking vasoconstriction on blood vessels

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Antihistamines

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control motion sickness. Dimenhydrinate (Dramamine) and Diphenhydramine (Benadryl)

decrease impulses sent from the vestibular apparatus to the emetic center during motion. Block the H1 receptors in the CRTZ. Less effective in blocking vomiting stimulus caused by intestinal CNS stimulation (gastroenteritis)

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Anticholingeric Drugs

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Block the effect of acetylcholine neurotransmitter(antiparasympathetic drugs). Also decrease secretions by the intestinal tract and overall gut motility

Aminopentamide, Atropine,

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Prokinetic Drugs

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Increases GI motility

Metoclopramide (Reglan), Cisapride
useful for intermittent vomiting of bile and mucus in dogs. Cisapride is not dopamine blocking. Serotonin antagonistic effects.

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Serotonin Antagonists

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also called 5-HT receptor antagonists. Ondansetron (Zofran)

blocks stimulation fo 5-HT receptors on the CRTZ

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Antidiarrheal Drugs

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drugs that change intestinal motility or reduce secretions that contribute to diarrhea.

Diarrhea occurs because the fluid secretion into the intestinal lumen and fluid absorption from the lumen has been uspet resulting in a net increase in fluid in the feces

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Anticholinergics

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Aminopentamide (Centrine)

work against the effects of the neurotransmitter acetylcholine. Reduce spastic colonic contractions and diarrhea associated tenesmus. Make small intestine diarrhea worse. Also called parasympatholytic drugs

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Opioid Narcotic Drugs

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Diphenoxylate (Lomotil), Loperamide (Imodium)

contain a subtheraputic dose of atropine designed to produce dryness in the mouth to dissuade abuse. They exert some analgesic effects that can mask abdominal pain. Also decrease gut motility and slow the transit time of intestinal content increasing the contact time between the bowel mucosa and pathogenic bacteria

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Antiinflammatory Drugs

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Bismuth subsalicylate (Pepto-Bismol, Kaopectate), Flunixin meglumine (Banamine), Sulfasalazine (Azulfidine)


include asprinlike compounds.

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Adsorbents and Protectants

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Activated Charcoal, Kaolin/pectin, Bismuth

Adsorbent makes other substances adhere to its outer surface, thus reducing the contact of that substance with the intestinal wall. Protectants cover the intestinal wall to form a physical barrier that protects the wall from contact with irritating or disease-producing compounds

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Kaolin/pectin

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adsorbs bacteria and their enterotoxins reducing their hypersecretory effect on the intestinal tract. Can decrease absorption of some antibiotics and cardiac drugs

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Activated Charcoal

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adsorbs enterotoxins and ingested poisons to its surface preventing them from contacting bowel wall. Seldom used to decrease diarrhea

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Bismuth

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antisecretory effects in diarrhea

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Laxatives and Stool Softeners

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Laxatives, cathartics, and purgatives are used to increase fluid content of the feces, making them softer and easing or promoting defecation

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Degrees of Aggressiveness

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Laxatives are most gentle. Cathartics are marked for their evacuating effect. Purgatives are the most potent and used when exavuation of the bowel is goal

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Emollient Laxatives

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Mineral oil, Cod liver oil, White petrolatum, Glycerin, Docusate sodium succinate (Colace)

lubricant oils and stool softeners. Mineral oil commonly used in horses with impaction. Cod liver and white petolatum commonly used in cats and dogs. Dissolve lipid-soluble toxins. Glycerin used as a suppository.

Docusate sodium succinate changes the surface tension of the fecal material allowing water to penetrate the fecal material and soften it.

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Bulk Laxatives

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pull water into the bowel lumen by osmosis or retain water in the feces.

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Cathartics

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osmotic cathartics and irritant cathartics. Osmotic are more aggressive than bulk laxatives

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Osmotic Cathartics

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Hypertonic salts (milk of magnesia, epsom salts), Latulose

Salts - poorly absorbed and create strong osmotic force to attract water into the bowel lumen. Can increase peristalsis and thus facilitate movement of the fecal material.
Lactulose - poorly absorbed sugar osmotic cathartic used to treat chronic constipation and reduce ammonia absorbed from the colon

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Irritant Cathartics

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castor oil

irritate the bowel resulting in increased peristaltic motility and some increased secretion by glands in the intestinal tract

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Antacid/Antiulcer Drugs

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given to decrease stomach acidity thus reducing gastric irritation caused by hyperacidity. Systemic or non-systemic. Nonsystemic are administered by mouth to neutralize acid molecules directly by chemically converting the strong acid to weaker acid. Systemic must be absorbed, circulate, and attach to receptors of the cells of the stomach to produce their effect

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Nonsystemic antacids

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Magnesium products (Riopan, Mylanta), Aluminum products (Amphojel), Combination magnesium and aluminum (Maalox), Calcium products (Tums, Rolaids).

Calcium and aluminum can cause constipation. Calcium are prone to gastric acid rebound syndrome. change in pH or the electrolytes may interfere with absorption of other drugs from the bowel.

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Systemic antacids

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H2 blockers, Cimetidine (Tagamet), Famotidine (Pepcid), Rantidine (Zantac), Omeprazole

H2 antagonists or H2 blockers because they block the H2 histamine receptor located on oxyntic cells in the stomach. Stimulus for gastric acid production is decreased. Omeprazole is an acid pump blocker. shuts off the hydrogen ion pump therefore decreases the acidity in the stomach

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Sucralfate (Carafate)

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antiulcer drug (gastric band-aid) it forms a sticky paste in the stomach that binds with the proteins found in ulcers. also stimulates prostagladin release, which promotes gastric protective mechanism and increases mucus production. Requires acidi environment

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Ruminatoric and Antibloat Medications

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ruminatoric drugs stimulate an atonic (no muscle tone) or flaccid rumen. Combat rumen stasis.

Antibloat - either reduce numbers of rumen microorganisms that produce gas or break up bubbles formed in the rumen with frothy bloat

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Neostigmine

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Neostigmine
combines with enzyme acetylcholinesterase and prevents it from breaking down into acetylcholine. results in increased GI stimulation.

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Dicotyl sodium succinate

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reduces the viscosity of rumen contents, which allows the foam to dissipate

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Antimicrobials

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Metronidazole (Flagyl), Sulfasalazine (Azulfidine), Tylosin (Tylan)

not usually needed or indicated for most common GI problems.