pharm gi 3

the antidote for metoclopramide toxicity is methylene blue :)

opiates, bulk-forming agents

loperamide, diphenoxylate, difenoxin

stimulate mu opioid receptors in the gut, reducing/abolishing peristalsis in the colon (slows movement, increases opportunity for fluid absorption). Also enhances anal sphincter tone and rectal distension relaxation reflex.

Loperamide does not penetrate the blood-brain barrier (removed by P-glycoprotein transporters), so few euphoric effects. Loperamide/diphenoxylate have low solubility, so IV drug abuse risk is minimal.

diarrhea

use with select severe, infectious diarrhea (interferes with the clearance of the bad bacteria). pts with preexisting GI motility reduction (severe inflammatory bowel disease)

constipation. possible abuse potential (CNS effects).

kaolin/pectin, attapulgite, bismuth

not fully known -- may provide additional structural integrity to stool (they are essentially clay that is able to absorb a large amount of water), may bind enterotoxins that caused the diarrhea in the first place.

doesn't selectively bind water, so can also bind drugs and nutrients (separate administration)

stimulants, bulk, osmotics, softeners, peripheral opioid antagonists

sennosides, castor oil, bisacodyl

irritate the intestinal wall, leading to an accumulation of fluid and electrolytes as well as increased motility (mechanism unknown)

designed to be released in the intestine but not before, or would cause irritation of the stomach (don't split/crush pills)

constipation

diarrhea

castor oil contains ricin (poison!)

psyllium

"ruffage" -- fiber cannot be broken down, so increased fiber causes increased bulk of stool which causes increased GI motility. fermentable fibers help increase bacterial content/bulk of stool, nonfermentable fibers draw water into the stool.

conditions where increasing bulk would be bad (obstruction, megacolon)

diarrhea, abdominal distension