Ch.3: Drug Absorption, Transport, and Distribution Flashcards
absorption*
a combined measure of the rate and amount of drug that moves from the administration site into the bloodstream. Is NOT a good indicator of a drug’s therapeutic actions(s)
Why is lidocaine basically unusable for any systemic effect?*
more than 95% is metabolized in its first pass through the liver (First-Pass Effect)
How is bioavailability determined?*
1) admin. drug to group of normal adult animals of target species
2) compare route of interest to IV using same dose
3) measure plasma drug levels and determine AUC
What is the major driving force for drugs to move into the vasculature?*
the concentration gradient of unbound soluble drug
What is xylazine classified as?*
sedative-analgesic agent. An alpha-2 agonist
Which domestic species is particularly susceptible to xylazine?*
Ruminants (esp. cattle)
Primary use of xylazine*
sedative-analgesic
major side-effects of xylazine*
lowers BP, causes CV depression, animal can pass out and collapse
4 methods of passive diffusion*
- facilitated diffusion
- filtration
- active transport
- pinocytosis and phagocytosis
The net rate of membrane diffusion is determined by:*
- drug size/MW
- lipid: water partition coefficient
- net charge (ionization state)**
How do amide-type local anesthetics work?*
contain a secondary amine that becomes protonated (cation) in an acidic environment
local anesthetics are mostly acids or bases?*
bases
what is “free-basing”?*
putting a drug in its free base form so it is more effective as a local anesthetic (i.e. cocaine)
How does lidocaine change in acidic vs. basic environment?*
in an acidic environment, more lidocaine will exist in a protonated form than the uncharged form, and it will be less likely to move through membrane barriers
For highly lipophilic drugs, distribution depends exclusively on:*
tissue blood flow
some drugs undergo ____ for termination of effect*
redistribution
Most prevalent mech. by which drugs cross biological (cellular) membranes? **
passive diffusion
Increasing lipid:water partition coefficients correlates with:
higher conc. of drug within the membrane and consequently a greater rate of passive membrane diffusion
basic drugs tend to accumulate in:
fluid compartments having pH less than the pKa of the drug (reverse for acidic drugs)
