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GI Pharmacology


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Drugs for acid related disorders
H2RA, PPI, Prostaglandin E analogue, Cytoprotective agents, anti H. pylori regimens
Drugs for nausea/vomiting
5HT antagonist, histamine H1 antagonist, Dopaminergic D2 antagonist, Benzodiazepines, corticosteroids, cannabinoids
drugs for variceal hemorrhage
somatostatin, octreotide, vasopressin
list H2RAs (4)
cemitidine (tagamet), ranitidine (Zantac), famotidine (pepcid), nizatidine (axid)
reversible, competitive inhibition of histamine-2 receptor
which H2RA interferes with Cyt P450?
rare, serious side effects of H2RA?
leukopenia, thrombocytopenia, anemia, bradycardia, hypotension
clinical uses of H2RAs
GERD, PUD, non-ulcer dyspepsia, stress gastritis prevention
PPI agents available
omeprazole (Prilosec), lansoprazole (Prevacid), rabeprazole (Aciphex), pantoprazole (Protonix), esomeprazole (Nexium)
prodrugs, irreversibly bind H+/K+ atpase, concentrated 1000x in acidic canaliculi
PPI pkinetics
short serum t 1/2 ~1.5 hrs, but duration of action is 24h, takes 3-4 days before full potential is reached
which PPI inhibits Cyt P450?
omeprazole (Prilosec), lansoprazole (Prevacid), rabeprazole (Aciphex), pantoprazole (Protonix), esomeprazole (Nexium)
Clinical uses of PPIs
GERD, PUD, non-ulcer dyspepsia, stress gastritis prevention, Zollinger Ellison Sydrome
what is the prostaglandin E analogue?
misoprostol (Cytotec)
how does misoprostol work?
stims mucus and bicarb secretion and enhances mucosal blood flow
problem with misoprostol?
lots of side affects: diarrhea, uterine bleeding, abortion
prokinetic agents?
meoclopramide (Reglan), bethanechol, macrolides (erythromycin)
metoclopramide MOA
stims release of ach from myenteric neurons, increases LES pressure and enhances gastric emptying
metoclopramide Side Effects:
neuropsychiatric side effects in 10-20%, EPS
uses of metoclopramide
Gastroparesis, anti-emetic, GERD, non-ulcer dyspepsia
where is the brainstem vomiting center?
lateral medullary reticular formation
what provides input into brainstem vomiting center?
CTZ, vestibular system, pharynx, GI tract, cerebral cortex
5HT3 serotonin antagonists
ondansetron (zofran), granisetron (Kytril), dolasetron
five types of laxatives
bulk forming, stool surfactant, osmotics, PEGs, Stimulants
what is a bulk forming laxative?
indigestible substance that swells w/ water. Fiber: metamucil
what is a stool surfactant agent?
Colace: acts as detergent to soften stool
what is an osmotic laxative?
non-absorbable osmotically active agent: milk of magnesia
list some stimulant laxatives:
bisacodyl (ducolax), phenolphthalein (ExLax)
list 3 anti-diarrheal agents
loperamide (Immodium), diphenoxylate, octreotide
mechanism of loperamide?
slows motility through direct action on intestinal nerves
diphenoxylate mechanism?
opioid agonist
Octreotide mechanism?
synthetic peptide, mimics somatostatin
Drugs used for IBS?
antispasmodics and antidepressants, alosetron and tegaserod
list some antispasmodics?
Bentyl (dicylomine HCl), Levsin (hyocyamine sulfate)
Mech of alosetron?
selective 5ht3 antagonist, decreases visceral sensitivity
mech of Tegaserod?
5HT4 agonist, prokinetic effect
5-ASA drugs
pentasa, asacol, rowasa
5-ASA mech?
inhibits NFkB, transcription factor for pro-inflammatory cytokines
key to 5-ASA delivery/bioavailability?
works topically, so need to deliver high concentration
when to use 5-ASA?
first line against UC and CD
which glucocorticoids used for IBD?
prednisone and prednisolone
glucorticoid MOA?
anti-inflammatory and immunosuppresive: block TNF-a, IL-1, IL-8, NOS, phospholipase A2, cox2
side effects of glucocorticoids?
petechiae, bruising, striae, moon face, acne, HTN, ifxn
how do you dose glucocorticoids?
use high dose to induce remission, after stabilization, slowly taper dose
Azathioprine MOA
intracellular accumulation of 6-thioguanine tns inhibts pathways of purine synthesis/repair, causing inhibition of cell division
p-kinetics of AZA/6MP
AZA quickly metabolized to 6MP, 6MP inactivated by TPMT, converted to active 6TG by HGPRT
problem with giving AZA?
if px has TPMT deficiency, get toxic levels of drug
adverse effects of AZA:
allergic, dose related: BMS, anemia, leukocytopenia, thrombocytopenia
methotrexate MOA
inhibits DHFR, which is critical for production of thymidylate and purines
MTX toxicities
BMS, GI ulcer, stomatitis, alopecia, rescue with tetrahydrofolate
which IBD benefits from MTX?
CD, not UC
what is infliximab?
monoclonal anti-TNFa
which IBD benefits from infliximab?
UC and CD
Drugs for IBD?
5-ASA, prednisone, AZA, MTX, infliximab, abx, cyclosporine

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