Ch. 6-Drug Absorption Flashcards
How long is the small intestine?
20-23 ft (6-7 m)
what is the most important part of the GI tract for drug absorption?
small intestine
How long is the large intestine?
5 ft (1.5 m)
systemic administration
absorbed directly from site of administration into bloodstream and spreads to site of action
nonsystemic administration
drug is localized to the area and not intended to spread
-not always successful, sometimes drug spreads anyway and causes side effects
where is a drug absorbed that is taken orally?
small intestine
villi
line the intestine, they increase surface area for drug absorption
which route is most common and patient preferred?
oral route
drug absorbed by:
4 ways
- passive diffusion (primary)
- carrier mediated (fastest)
- intestinal drug efflux (spits drug out of cell, limits absorption)
- transcytosis (receptor mediated, inefficient)
4 classes of drugs
Class 1-high solubility and permeability (best)
Class 2-low solubility and high permeability
Class 3-high solubility and low permeability
Class 4-low solubility and permeability (worst)
normal stomach pH
1.0-3.5
parts of small intestine
duodenum, jejunum, and ileum
normal duodenum pH
5.5-6.5
duodenum
first part of small intestine, receives stomach contents
normal jejunum pH
6.5-7.0
jejunum
2nd part of small intestine, about 40% of the small intestine total
normal ileum pH
7.0-7.5
ileum
last part of small intestine (end), about 60% of total small intestine
why does the pH raise after leaving the stomach?
the stomach is very acidic, and after the contents leave the stomach they are neutralized by the pancreas, so the pH gets closer and closer to 7
Drug properties that make oral administration impossible
- drug is an irritant
- drug has poor lipophilicity (can’t passively diffuse)
- large molecular size (can’t passively diffuse)
Patient properties that make oral administration impossible
- unable/unwilling to swallow meds
- patient needs more immediate response
- GI distress or disease
- they are taking meds that are incompatible with the drug
parenteral route
given somewhere other than the GI tract
-ex) subcutaneous, intravenous, intramuscular
rectal route
among slowest absorption, reserved for situations where oral administration is impossible
local administration
nonsystemic, usually blood absorption doesn’t occur
-lower doses can be used
local parenteral delivery
injecting the drug near the site of action
-ex) intracardiac, intrathecal (cerebrospinal fluid), intralumbar
