Exam1Lec1Pharmacokinetics Flashcards
What are two main concepts about drugs
- Drugs mask problems, not solve them
- All drugs are poison at high concentration
What are pharmacokinetics?
The process by which drugs are absorbed, distributed within the body, metabolized, and excreted
Absorption
process which drugs enter systemic circulation
100% of a drug is absorbed if administered?
IV
Distribution
drugs reach its site of action
Elimination
process where drugs are enzymatically altered (biotransformation) mainly in liver and excreted in kidneys
Only _____ drugs can cross the BBB
highly lipid soluble/non-ionized
hydrophobic
Factors in transfer of drugs across membranes
- molecular size and shape
- lipid: water partition coeffic. (solubutlity of drug)
- most drugs are WA or WB
determines solubility of the drug and affects distribution
lipid:water partition coefficient
Nonionized drugs ____ cross the cell membrane. Ionized drugs ____ cross.
can, cannot
weak acid ___ an H+ ion
gives
equation goes to the right becaause lower pH means more H+ pushing the equation twoards unionized form
weak base ___ an H+ ion
takes
strong acids ____ compared to WA
completely dissociate
For weak acid, the degree of ionization depends of what?
pH
decrease pH = ___ more ionized
base
increase pH = ____ more ionized
acid
Only the ____ form of the drugs can readily cross the cell membrane
non-ionized (HA/B)
no charge so free to go around
Henderson-Hasselbalch equation: Weak acid vs. WB
WA:
pH = pKa + log10 (I/U)
WB:
pH = pKa + log10 (U/I)
remember I owe U for WA
HH eq allows the calculation of degree of the ionization for weak acids or weak bases
Term for when drugs become trapped on one side of a lipid mucosal barrier
ion trapping
weak acids get trapped on ____ side
basic
weak bases get trapped on ____ side
acidic
Processes of drug transfer
- Passive diffusion
- Active transport
- Facilitated diffusion
Passive diffusion:
1. movement on gradient?
2. saturable?
3. carrier mediated?
4. extra detail?
high to low [ ] (down graidient)
NOT saturable
NOT carrier med
it is the most common and the higher the lipid: water partition coefficient the faster is the passive diffusion
ex: ethanol
Active transport:
1. movement on gradient?
2. saturable?
3. carrier mediated?
4. extra detail?
Low to High (up gradient) (only transport that does this)
Saturable
Carrier mediated
Needs Energy
ex: penicillin in kidney p-glycoprotein and MRP are the main transporters of drugs
What are xenobiotics?
Foreign chemical substance that goes through active transport
What does fixed capacity mean?
You reach vmax so you cant go higher than that
Faciliated diffusion:
1. movement on gradient?
2. saturable?
3. carrier mediated?
High to low ( down gradient)
Saturable
Carrier mediated
ex: amino acids transport into brain
What is bulk flow?
movement of molecules through capillary junction
What is pinocytosis?
Formation and movement of vesicles. it plays a minor role in drug transport across the membrane
What are the factors that affect drug absoprtion?
solubility, concentration, circulation, surface area, time
Drug absorption:
Solubility
aqueous solution vs. oily solution
pH (ex: aspirin)
How does Concentration affect drug absoption?
high concentration of drug absorbed more quickly
How does circulation affect affect drug absoprtion?
increase circulation = increase absorption
decrease circulation = decrease absorptions
Drug absorption:
Surface Area
Intestinal mucosa = oral meds
Pulm. alveolar epithelium = anesthetics
Skin = patches
antibitoics get through bodies through lungs
