What is the predominant ANS tone in the GI?
What is the effect of sympathetic input into the GI on the walls? What receptors mediate this?
the walls of the GI relax via a2 and B2 binding
What is the effect of sympathetic input into the GI on the sphincters? What receptors mediate this?
they contract via a1 binding
What is the effect of sympathetic input into the GI on secretions?
There is none
What is the effect of parasympathetic input into the GI on the walls? What receptors mediate this?
contraction via M3 receptors (parasympathetics also cause sphincters to relax via M3 binding and secretions to increase via M3 binding)
What are the effects of cholinergic (Ach) agonists (or AchE inhibitors)?
Bronchorrhea, Bronchospams, Bradycardia
What are the effects of cholinergic (Ach) antagonists (or AchEs)?
constipation and urinary retention
large bronchiole dilation
decreased glandular secretions
restlessness, confusion, delirium, hallucinations
What is the enteric nervous system?
The ENS is involved in sensorimotor control of the GI and this consists of both afferent sensory neurons and a number of motor nerves and interneurons that are organized principally into two nerve plexuses: the myenteric (Auerbach's) plexus and the submucosal (Meissner's) plexus.
Where is the myenteric plexus located and what does it do?
It's located bettwen the longitudinal and circular muscle layers of the GI wall and plays an important role in the contraction and relaxation of GI smooth muscle
What does Meissner's plexus do?
It's involved in secretory and absorptive functions of the GI epithelium, local blood flow, and neuroimmune activities
What is the primary neurotransmitter of the ENS?
What other neurotransmitters are involved in ENS control/modulation?
Dopamine (pre- and postsynaptically inhibit Ach release and relax the esophageal sphincter)
Enkephalin and related opiod peptides
Serotonin (5-HT) (promote Ach release)
ATP, CGRP, CCK
What is Metoclopramide?
A drug used to treat N/V and gastroparesis via its gastrokinetic actions
How does Metoclopramide work?
This drug possesses both dopaminergic (inhibits pre and postsynatic D2 receptors to promote Ach release and prevent relaxation of the esophageal sphincter and stomach) and serotonergic modulatory activity (stimulatory to promote Ach release), leading to coordinated contractions that enhance motility in the upper GI tract
What is the major downside of Metoclopramide?
it causes tardive dyskinesia (involuntary movements of the tongue, lips, face, trunk, and extremities) and
akathisia (movement disorder characterized by a feeling of inner restlessnes and a compelling need to be in constant motion)
-cardiac arrhythmias and bradycardia
What part of Metoclopramide causes BOTH tardive dyskinesia and akathisia?
the dopamine modulation
What are the main types of laxatives?
dietary fiber and bulk-forming
How do antidiarrheals work?
they work to decrease stool fluidity (i.e. water absorbers), to antagonize cholinergic NS activity, or to activate the opiate receptors in the ENS
What is Inflammatory Bowel Disease?
this is a term that encompasses ulcerative colitis and Crohn's disease
What causes IBD?
There is suggested dysbiosis of normal intestinal homeostatic relationship between intestinal mucosa and normal commensals, leading to inflammation (including TNFa)
What are some TNFa-antagonists used in the tx of IBD?
What are natalizumab and vedolizumab?
these bind the a4B7 integrin on T cells in the bloodstream, blocking its interaction with MAdCAM-1, which is mainly expressed on gut endothelial cells, to prevent extravasation of T cells into tissue (mostly used for UC)
What are the AEs of a4B7 integrin inhibitors (natalizumab and vedolizumab)?
-immunosuppression (avoid giving live vaccines during tx)
-progressive multfocal leukoencephalopathy
What causes the rare progressive multfocal leukoencephalopathy seen with a4B7 integrin inhibitors?
JC virus, which is normally present and kept under control by the immune system
How would mild UC be treated initially?
Sulfasalazine, and its metabolite 5-ASA, as anti-inflammatories in the gut (note that these work primarily in the gut because they are poorly absorbed)
How should you procede if Sulfasalazine doesnt work for initial UC tx?
systemic glucocorticoids (note that if UC or CD are moderate to severe at presentation, you can start tx with this)
How should you procede if systemic glucocorticoids work but then the UC pt. relapses?
try immunomodulators like thiopurine, and then go to TNF-a inhibitors
How should mild CD be tx initially?
topical glucocorticoids (distal colonic disease) or budesonide (distal ileal involvement)
One of the most significant and consistent AEs to chronic opiate use is what?
How do opiates affect the gallbladder?
they promote contraction, spasm of the sphincter of Oddi and decreased secretions, leading to biliary pain and delayed digestion
How do opiates affect the gastroduodenum?
they decreased gastric emptying and increase pyloric tone
initially increase duodenal motiltiy followed by quiescence
increased gastric acid secretion
all promoting anorexia and N/V
How do opiates affect the small bowel and colon?
they increased tone, increase transit time, and increase absorption
and decrease secretion
all promoting constipation, cramps, and delayed digestion leading to hard, dry stool
How do opiates affect the anorectum?
they decrease rectal sensitivity and increase internal sphincter tone
leading to incomplete evacuation
What are some ways that drugs can induce diarrhea?
-osmotic diarrhea by drawing water into the GI
-secretory diarrhea by imparing Na+ absorption (e.g. NSAIDs), causing Cl- and HCO3- to be secreted into the GI
-affecting cholinergic tone
What is inflammatory diarrhea?
disruption of colonic flora precipitating C. difficle colitis or damaging thr gastric mucosa, usually via antimicrobials or drugs that affect intestinal pH
How does C. difficile diarrhea occur?
disruption of the acid-base environment or epithelial homeostatsis is in the case of PPIs, H2 antagonists, and immunosuppressants
What drugs produce diarrhea by virtue of their MOA?
orlistat (weight-loss) and cholestyramine (for hypercholesterolemia)
What other drugs list diarrhea as an AE?
-metformin via decreased glucose absorption (aka osmotic diarrhea)
What are some drugs that frequently cause C. difficile diarrhea?
1st, 2nd, and 3rd gen cephalosporins
What are some drugs that cause noninfectious watery diarrhea?
a-glucoside inhibitors such as acarbose and miglitol
What are some drugs that cause noninfectious secretory diarrhea?
What are some drugs that cause noninfectious diarrhea via altered motility?
cholinergic drugs, macrolides, and metoclopramide
What are some drugs that cause noninfectious fatty diarrhea?
What are some drug classes most likely to cause constipation?
T or F. Decreased intestinal P-gp activity would lead to dramatically increased drug bioavailability
What is the pH of the stomach?
How do NSAIDs affect the GI?
they inhibit the production of prostaglandinds which results in increased gastric acid secretion and reduction of secretion of protective mucus and bicarbonate by epithelial cells
How does the use of antacids affect the co-administration of oral drugs?
some drugs, like doxycycline, tetracycline, and fluoroquinolones, require an acidic environment for absorption and antacids can chelate them (dont administer at the same time)
What drugs require an acid environment for absorption and are less bioavailable in the presence of H2 blockers?
Famotidine inhibits clearance of what drug?
All PPIs are substrates what what CYP?
2C19, and all but dexlansoprazole exert some degress of 2C19 inhibition, with pantoprazole being the weakest
What drug would be less effective if given with a PPI?
Clopidogrel, which requires metabolic (2C19) activation
How does cholestryamine work?
it sequesters bile salts in the GI tube and prevents absorption to lower cholesterol
How do opiate receptors work?
presynaptically they inhibits release of neurotransmitter by acting as a CCB, and postsynaptically they hyperpolarize potassium channels making it less responsive to neurotransmitter to modulate cholinergic activity
How does erythromycin affect the GI?
it stimulates motilin receptors in the duodenum to "clean" the stomach after a meal (releases cyclically) as IV eryhtromycin lactobionate
used commonly before surgery to avoid aspiration pneumonia durign surgery
What drug can be used to reverse opitae induced constipation but doesnt affect the analgesic effects of opiates?