Test 1-Mass transfer Flashcards
(49 cards)
What is mass transfer (definition)?
A net movement of mass from one location to another in response to applied driving forces
When and where in the human body does mass transfer happen?
Occurs across different types of cell membranes and under different physiological conditions
What studies is mass transfer important for?
Dosage form design
ADME
What does diffusion of a drug through biological membrane involve?
Diffusion
Partitioning
Permeation
What is the diffusion step?
The drug’s diffusion through the aqueous medium that bathes the membrane
What is the partitioning step?
Passage of the drug molecules form the aqueous medium of the GI fluids into the lipid bilayer of the membrane
What is the permeation step?
Diffusion of the drug through the membrane
What is drug permeation?
Drug transfer - molecular diffusion of the drug through relatively non porous media
What does drug permeation depend on?
Drug partitioning
The structural nature of biological membrane
The nature of diffusion layer (GI content)
What is drug partitioning?
The ability of the drug to distribute in a mixture of aqueous and lipid system
How is drug partitioning across biological membrane measured?
By using a mixture of octanol (nonpolar) and water (polar) to get Kd and then Lop P which represents the drugs lipophilicity
What does lipophilicity affect?
Aqueous solubility (decreases with an increasing Log P)
Permability (increases with increase in Log P)
How do most therapeutic agents exist?
As either weakly acidic or basic in nature
What does aqueous solubility of a drug depend on?
pKa or the dissociation constant
pH of the solution
TF: The ionized states of a drug exhibit greater aqueous solubility than un ionized states
True because the ionized states are polar
What does pH of the surrounding fluid affect for the drug?
Solubility
Dissolution
Permeation
What kind of drugs are predominantly present in their un-ionized forms in the GI fluid in the stomach and upper part of the duodenum?
Weakly acidic drugs because of the lower pH which aids in their permeation in these areas
What kind of drugs are poorly absorbed in the stomach?
Weakly basic drugs
They exist largely in the ionized states at the GI pH
Why is the lipophilic nature of drugs important?
Because the biological membranes are lipid barriers
What is the most common process for the passage of drugs through biological membranes?
Passive diffusion
What is passive diffusion?
When drugs diffuse across a cell membrane from a region of high concentration (GI fluid) to a region of low concentration (blood)
What is diffusion rate directly proportional to?
The gradient
TF: small particles pass the membranes much slower than large molecules
False
They diffuse faster
What is passive diffusion of drugs governed by?
Fick’s law of diffusion
