Solubility of substance?
Amount that goes into a solution when equilibrium is established between the solute in solution and the excess (undissolved) substance
Solution process?
- Drug molecule removed from its crystal
- Cavity from the molecule is created in the solvent
- Drug molecule inserts into this cavity
Saturated solution?
Contains drug at the limit of its solubility
Factors affecting drug solubility?
Temp, shape/SA/hydrophobicity of drug/pH/solubilising agents/crystal characteristics
Effect of increasing temp on solubility?
Increases solubility (higher energy)
Effect of increasing mp/bp on solubility?
Decreases solubility (stronger interactions)
Effect of ionisation (extreme polarity) on solubility?
Increases solubility - causes increases hydrophilicity
Why will drugs partition between solvents?
Due to difference in solubility in difference phases (across cell walls)
What is log P (partition coefficient) a measure of?
Lipophilicity/hydrophilicity (unionised form of drug)
What is log P?
Ratio of conc of drug in oil/hydrocarbon to conc of drug in water
If log P greater than 0?
Drug is lipophilic
If log P less than 0?
Drug is hydrophilic
Structure of crystals?
Highly ordered arrays of molecules/atoms held together by non-covalent interactions
Polymorphism?
Molecules arrange themselves in different ways in the crystal
