Gastrointestinal Drugs Flashcards
What are the 6 types of drugs used for treating gastrointestinal diseases?
- antiemetics
- drugs to treat diarrhea
- drugs to treat inflammatory intestinal diseases
- prokinetic drugs
- drugs to treat GI ulcers
- laxatives and cathartics
What neural plexuses are located in the walls of the gut? What is the ENS extensively innervated by?
- SUBMUCOSAL PLEXUS: under the submucosa
- MYENTERIC PLEXUS: between the inner circular muscle layer and the outer longitudinal muscle layer
nonadrenergic-noncholinergic (NANC) nerve fibers
ENS:
What is emesis? Where are all emetic signals coordinated? What supplies afferent input?
complex, protective, reflex activity with coordination centered in the brainstem
emetic center (vomiting center) in the mid brainstem
chemical trigger zone (CTZ), which is sensitive to drugs and toxins in the blood
What happens when emesis is pharmacologically induced? What are the 2 main purposes of pharmacologic emesis?
the anterior portion of the digestive tract is emptied
- preparation for induction of general anesthesia
- treatment of ingested, noncorrosive poisons
What are the 2 ways that substances induce emesis?
- distending the pharynx, esophagus, stomach, or duodenum (hollow organs)
- irritating the epithelium of the GI tract (gastric mucosa or pharynx)
What are 4 examples of peripherally acting (reflex) emetics?
- warm water/saline distends GI tract (can also dilute toxins)
- DOGS - oral administration of a solution of warm, saturated sodium chloride
- pharyngeal placement of a small amount of plain table salt or neutral salt crystals, such as sodium carbonate
- orally administered hydrogen peroxide (3%), copper sulfate (1%), or zinc sulfate (1%) —> careful of fatal aspiration pnemonia
What do prokinetic drugs do? What is a common instance they are used?
drugs that enhance the transit of intraluminal content and stimulate gastric emptying and rumen/intestinal motility
after surgery when intestinal motility is decreased, which can lead to ileus
What is Metoclopramide?
lipid-soluble derivative of para-aminobenzoic acid that acts as a central (antidopaminergic) and peripheral (antidopaminergic/cholinergic agonist) prokinetic drug
What are the 7 actions of Metoclopramide?
- D2 antagonist
- serotonin (5-HT3) antagonist
- serotonin (5-HT4) agonist
- increase the release of ACh in the GI tract
- increase gastric emptying
- increase the tone of the esophageal sphincter
- stimulate motility of the duodenum (less effective distally)
What endocrine effect does Metoclopramide have?
transient increase of prolactin and aldosterone
What are the 5 uses of Metoclopramide in small animals? When is use contraindicated?
- stimulate normal upper motility following corrected surgery
- volvulus
- postoperative ileus
- gastric ulceration
- idiopathic gastroparesis
GI obstruction or perforation
What are 2 uses of Metoclopramide in horses? What are 2 common undesirable side effects?
- reduce postoperative ileus
- stimulate small intestine (NOT large bowel)
behavioral changes and abdominal pain
Why is the use of Metoclopramide in ruminants less common? What can it be used successfully in? What side effect can occur in calves?
little usefulness in cattle - may increase rumen motility in cattle/sheep
cattle with functional pyloric stenosis
doses higher than 0.1 mg/Kg can cause severe neurological signs
Why was Cisapride removed from the market?
causes serious arrhythmias and death in people (not reported in animals)
- available via compounding pharmacists
What 3 effects does Cisapride have on ENS receptors? How does it effect the GI tract?
- 5-HT4 agonist on myenteric neurons
- 5-HT3 antagonist
- enhances ACh release at the myenteric plexus
ALL GI sites - esophagus, stomach, jejunum, ileum, small intestine, colon
What are the 4 major therapeutic uses of Cisapride?
- gastroesophageal reflux
- delayed gastric emptying
- small bowel motility disorders
- chronic constipation in cats (affects colonic smooth muscles)
How does Cisapride compare to Metoclopramide?
- more effective for increasing lower esophageal sphincter tone in dogs
- causes antegrade contraction along the whole GI tract
What is Domperidone? How does its mechanism of action compare to other drugs of the same class?
D2 antagonist that may also have α1-receptor antagonistic and serotonin (5-HT2) antagonist
mechanism of action and prokinetic effect is similar to metoclopramide
- accelerates small intestinal transit
- colonic activity unaffected
How has Domperidone been used in horses? What affect does the approved dose have?
treat fescue toxicity and agalactia
- forage-related disease involving endocrine disruptive effect of ergot alkaloids (from Neotyphodium coenophialum) on prolactin secretion
1.1 mg/Kg = oral absorption of 1-1.5% = no effect on GI function
- 5 mg/Kg = increased stomach emptying
How may Domperidone’s α2 antagonistic affects be used?
increases digital laminal microvascular flow, which may help treat laminitis
What is Erythromycin? How can it affect the GI tract?
macrolide antibiotic used to treat bacterial infections
at low doses (much lower than antibacterial dose), it stimulates GI motility
How does Erythromycin stimulate GI motility?
activated motilin receptors, allowing for motilin release from endocrine cells of the duodenal mucosa —> increases motor contraction
- most motilin receptors are on the stomach and proximal intestine
What is the main clinical use of Erythromycin? What are 2 major concerns?
increase gastric emptying and therapy of reflux esophagitis
- cause diarrhea by altering the normal bacterial flora of the intestine
- routine use can promote antibacterial resistance
Lidocaine is a well-known local anesthetic. How can it be used on the GI tract?
IV infusion of lidocaine improves intestinal motility in horses to reduce postoperative ileus
What are 3 common causes of postoperative ileus? What does this cause?
- sympathetic stimulation
- pain
- inflammation
inhibits smooth muscle motility in the intestine
How is Lidocaine thought to work as a prokinetic? What are 3 possible adverse effects? How can they be avoided?
not a direct prokinetic - may inhibit intestinal inflammation and reperfusion injury via suppression of painful stimuli
- muscle fasciculation
- ataxia
- seizures
- decrease infusion rate
What 3 peripheral opiate antagonists can act as GI prokinetics? How do they work?
Alvimopan, Methylnaltrxone, Naloxegol
block the activation of µ-receptors on the submucosal plexus, myenteric plexus, and longitudinal muscle of the ileum, which would have decreased propulsive motility of intestinal smooth muscle
How do Alvimopan and Methylnaltrexone compare in potency and duration?
(peripheral opiate antagonists)
Alvimopan > Methylnaltrexone
How is Alvimopan administered? What does it do?
(peripheral opiate antagonist)
orally —> low bioavailability (6%)
produces a local effect on the intestine to promote motility
What is Naloxegol used for?
oral treatment of opioid-induced constipation
What are the 4 principal drugs used to manage GI ulceration in small and large animals?
- histamine (H2) receptor antagonists
- sucralfate
- proton pump inhibitors (omeprazole)
- antacids
What are the 8 clinical uses of drugs that treat GI ulcers?
- gastritis
- gastric ulcers
- duodenal ulcers
- GI ulcer prevention
- esophagitis
- mast cell tumors
- hypergastrinemic syndromes
- prevention and treatment of NSAID-induced ulcers
How does HCl secretion in carnivores compare to humans?
carnivores = intermittent
humans = continuous
In which animals is GI ulceration most prevalent? What are 7 contributing factors?
horses
1. stall confinement
2. intense exercise
3. diet (high energy concentrated)
4. racing stress
5. intermittent feeding schedule
6. increased stomach acidity
7. use of NSAIDs
How do antacids work to treat GI ulcers? What are 4 examples?
neutralize stomach acid through a simple reaction to form water and neutral salt
- magnesium hydroxide
- aluminum hydroxide
- calcium carbonate
- sodium bicarbonate