What is distribution
Getting drug to site of action
What effects distribution (5)
- Protein binding
- Blood flow
- Membrane permeation ( lipid solubility)
- Tissue solubility ( pH and ionisation)
- Molecular size
Do plasma protein bound drugs excerpt action ?
No - only free drug
What can effect patients plasma proteins? (2)
Liver failure or kidney damage
NB plasma proteins made in liver
What is volume distribution?
How far drug travels
Lipophilic - large Vd
Water sol - small Vd
What is the acid dissociation constant pKa?
Strength of an acid
pH when 50% of drug molecules are ionised
Do lipids attract non ionised molecules?
Yes
Do aqueous sols attract ionised mols
Yes
Acidic drugs in acidic environments will be?
Non ionised ( move through lipid membranes)
Alkali drugs in alkaline solutions will be ?
Non ionised- move though lipid membrane
Acidic drugs in alkaline environments and alkaline drugs in acidic environments will be
Ionised ( will not move through lipid membranes
What effects drug distribution? ( 5)
- Drugs needs to cross cell membrane to produce effects
- Degree of ionisation (low better)
- Molecular weight ( low better)
- Lipid solubility ( high better)
- Concentration gradient ( high better)
