drug absorption and distribution Flashcards
3 factors to consider in drug absorbtion
- drug properties
- patient factors
- possible routes of admin
4 mechanisms of drug absorption (cellular)
- passive diffusion
- facilitated diffusion
- active transport
- phagocytosis
3 properties of drugs that affect absorption
- chem structure size etc.
- lipid and water solubility
- ionization
what is usual molecualr weight of drugs
250-450 Da
at what size can a lipid soluble drug diffuse across membrane
1000Da
what is partition coefficient
[drug in membrane]/[drug in buffer]
what does higher partition coeff. mean
more lipid soluble
what increase and decrease PC
incr- hydrophobic groups (benzene, CH3)
dec. - hydrophilic groups - OH, COOH,
what is the effect of drug ionization
uncharged form is generally easier to cross membrane
** what happens with higher Ka in acid and basic drug - when increase pH over pKa
acid - more ions
basic - less ions
what are drug transporters
proteins responsible for moving drugs into and out of cells
most common locations of transporters
apical layer of hepatocytes, enterocytes, tubular cells
2 main classes of drug tranporters
- uptake transporters
2. efflux transporters
why are transporters relevant
- also affects distribution and elimination
2. need to know if drug is a substrate, inhibitor, or inducer of transport
what is volume of distribution
volume of total body fluid that is absorbing the drug
4 drug properties that influence distribution
- size and structure
- lipid solubility
- degree of ionization
- protein binding
3 other factors affecting distribution
- blood flow
- cap. permiability
- barriers
what are the 3 body compartments and avergae size for 70kg male
- water - 42L
- fat - 14L
- bone - 5L
what is apparent vol. of distribution
hypothetical vol. into which drug is disseminated
when is apparent vol used
when want to compare withing different compartments of body
formula for Vd
total drug in body/intial plasma [c]
what does app Vd tell us
an idea if the drug is beyond the plasma
when does knowing Vd help
- idea of where drug might be distributed
- when predicting plasma [C]
- determining dose of drug to produce desired plamsa [C]
- deciding whether to dyalize when poisoned
