the antidote for metoclopramide toxicity is methylene blue :)
opiates, bulk-forming agents
Antidiarrheals -- opiates drugs
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.
opiates pharmacokinetics (availability)
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.
use with select severe, infectious diarrhea (interferes with the clearance of the bad bacteria). pts with preexisting GI motility reduction (severe inflammatory bowel disease)
opiates side effects
constipation. possible abuse potential (CNS effects).
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.
bulk-forming antidiarrheals interactions
doesn't selectively bind water, so can also bind drugs and nutrients (separate administration)
irritate the intestinal wall, leading to an accumulation of fluid and electrolytes as well as increased motility (mechanism unknown)
stimulant laxatives pharmacokinetics
designed to be released in the intestine but not before, or would cause irritation of the stomach (don't split/crush pills)
Laxatives side effects
Fun fact #1
castor oil contains ricin (poison!)
Laxatives -- bulk (dietary fiber) drugs
bulk laxatives MOA
"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.
bulk laxatives contraindications
conditions where increasing bulk would be bad (obstruction, megacolon)