Solutions in Pharmacy

A single phase system that contains a substance (the solute) dissolved in another substance (the solvent)

A distinct homogenous part of a system separated by definite boundaries from other parts of the system.

Th amount of substance that passes into a solution when an equilibrium is established between solution and excess solid (saturated solution is obtained)
- temperature and pressure dependent

1. A solute (drug) molecule is removed from its surrounding solute molecules (breaking the solute- solute bonds) (endothermic)
2. A cavity for the molecule is created in the solvent (breaking the solvent-solvent bonds) (endothermic)
3 The solute molecule is inserted into this cavity (forming solute-solvent bonds) (exothermic)

- ionisation
- solid state structure
- h-bonding capability
- ratio of polar to non-polar bonds

-polarity
- H-bonding capability
- pH (if solute is weak electrolyte)

Dielectric constant

-High dielectric constants (reducing attraction between oppositely charged ions)
- solvation (hydration in the case of water)
- acid base reactions with strong electrolytes (due to the amphiprotic nature of polar solvents)
- Hydrogen bonding between solvent and solute

- Low dielectric constant (does not reduce attraction between charged and polar groups)
- Aprotic (neither accept or donate protons)
- cannot form hydrogen bonds
- can interact with non-polar solutes via induces dipole interaction (solvent is less attracted to itself)

- Aqueous solutions
- Mixed solvent solutions
- Oily solutions

- Polar solutes (incl salts salts and H-bonding sytems) dissolved in water
- water soluble complexes dissolved in water

H - bonding and dipolar solutes dissolved in water with semi-polar co-solvents.

Non-polar solutes dissolved in oils or organic salts