af Mashaal M Alghamdi 12 år siden
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First Pass affect
absorption affects
The equation (Not required)
Importance of plasma protein
VD big= drug will distribute to other compartments= High risk and toxicity
VD small= High [plasma]= High risk and toxicity
VD = Bioavailability/ [plasma] at time= 0 sec. (L/KG)
Permeation peinciples
Where the drug distribute determination
Capillary permeability
Brain Capillary
Liver
BBB
Binding to plasma protein
Role of Plasma protein
high affinity drugs are better than low affinity when binding proteins
protein are variables in binding
When binding, drug deactivated
sequester drugs in a non diffusible form in the plasma
Degree of hydrophobity/lipidophilly of the drug.
Blood flow to a given site
Tissue
Bone, Fat
Total body water
Extracellular fluids
Plasma
It depends on
Effect of pH
Permeation Principles
Endocytosis/Exocytosis
Endo and Exo cytosis are almost working like Carrier mechanisms.
Special carrier mechanisms
Saturable process
Why?
Can go againts the [ ]
Can uses ATP (Active diffusion)
Lipid Diffusion
Henderson Hasselbalch law
Weak acids in Stomach. Weak bases in intestines
You can calculate charged and uncharged molc. at any given pH
Meaning you can calculate how much is absorbed
Uncharged drugs are absorped readily
Electrostaticity of lipid drugs attract water to be water soluable
Drugs migh be weak acids or bases.
Aqueous (Passive) Diffusion
Lipid-soluable drugs pass through membrane
Doesn't matter (size, charge)
Water-soluable drugs penetrate the cell membrane throuh aquoues channels
Increase size of drug, decrease absorption
Drugs move from high to low concentration
Disease state
Presence of other meds in the stomach
a drug might bind to another drug to prevent absorption
compete or carier metabolism
Presence of food (to dely)
Blood Supply
