Unionized
a molecule that doesn't have a charge associated with it.
Unionized
Which is more permeable? Ionized or Unionized
Ionized
Which is more soluble? Ionized or Unionized
Permeability
the ease with which molecules cross biological membranes. or the ease with which ions or molecules pass through the pore of channel proteins.
Solubility
degree to which a substance dissolves in a solvent to make a solution (usually expressed as grams of solute per litre of solvent).
pH partiton theory
the absorption of a weak electrolyte is determined mainly by the extent to which the drug exists in its unionized form at the site of absorption.
Acids
donate protons
Bases
accept protons
weak acids
When pH is < pKa by 2 units 99% is in the unionized state
weak acids
when pH>pKa by 2 units 99% in the ionized state
weak bases
when pH is > pKa by 2 units 99% is in the unionized state
weak bases
when pH < pKa by 2 units 99% is in the ionized state
weak base, alkaline
salts of weak bases will act like ___; make it more _____
weak acid, acidic
salts of weak acids will act like ___; make it more ____
Ampholytes
-bontain both acidic & basic functional groups
-can act as an acid or base depending on the pH of the solution
Zwitterion
the molecule possesses a positive and a negative ion
Isoelectric point
pH at which a molecule exists in the form of a zwitterion
Polyprotic Acids
specific acids that are capable of losing more than a single proton per molecule in acid-base reactions. (In other words, acids that have more than one ionizable H+ atom per molecule).
By transcellular or paracellular pathways
How do drugs permeate cell membranes?
Paracellular Transport
-transport through cellular junctions.
-involves passive diffusion (Fick's Law) and convective flow of water.
Transcellular Transport
-can be influx (transport into the cell) or efflux (out of the cell)
-utilizes 3 mechanisms of transport
partitioning & passive diffusion, carrier-mediated transport, vesicular transport
What are the 3 mechanisms of transcellular transport?
Passive diffusion
-drug should partition from donor site into membrane
-drug should partition from the membrane to receptor site
CM Active Transport
-involves carrier proteins or transporters
-drug can be transported against concentration gradient
-process requires energy
-carrier may be selective
-carrier system is saturable
-process may be competitive
CM facilitated diffusion
-transport occurs in the direction of the concentration gradient, i.e. high to low
-process does not require energy