Dissolution of a tablet into to bloodstream Flashcards
Define diffusion
Diffusion reflects the change of concentration of drugs over time
Define partitioning
Partitioning reflects the ability of uncharged molecules to partition between to immiscible media e.g. water and octanol or from a water based fluid into a membrane
Define mass transfer
Mass transfer is the net movement of mass from one location to another; absorption, adsorption, precipitation, dissolution, distribution are examples.
Define driving force
The driving force is the difference of chemical potential (change of Gibbs free energy with the number of particles) –
Give examples of mass transfer without additional forces
flow, electric field, pressure, transporters
What is the diffusion coefficient?
The characteristic parameter of diffusion. The diffusion coefficient, D, is a characteristic of the molecule in its environment
Diffusion is not a velocity, but instead…
represents how rapidly molecules cover an area
Which diffuse faster - small molecules or large ones?
Small
Why is partitioning relevant for drug discovery?
It separates between two immiscible liquid or phases (hydrophilic vs. lipophilic)
P (partitioning coefficient) =?
C(organic phase)/C(aqueous phase)
P(apparent)=?
Pxf(unionised)
Lp is what?
Membrane permeability
Lp=? (equation)
(DP)/h
where D=diffusion coefficient
P=Partition coefficient
What can influence the drug concentration with regards to partitioning and diffusion etc?
Complexation e.g. cyclodextrins, micellar solubilisation , adsorption and stability can influence this concentration
Name some factors drug absorption is influenced by
pKa, lipid solubility, drug’s molecular weight, or number of H-bonds
