Solutions and solubility Flashcards
solution
a homogenous mixture of 2 or more substances
solubility
the number of parts of solvent (by volume) that willdissolve one part of solute (by weight)
unsaturated solution
more solutedissolves.
No solid remains inflask.
saturated solution
no more solute dissolves. Undissolved solid remains in flask.
supersaturated solution
more solute than is normally possible.
Becomes unstable,crystals form
Aqueous solubility of a drug
the concentration at which the solution is said to besaturated. Any further addition of the drug will result in drug precipitation
when the components of a solution are of the same phase, are we more likely to talk in terms of miscibility or solubility?
miscibility
is dissolution the same as reaction
how would you tell a dissolution from a reaction
no
dissolution is a physical change, and can be reversed to the original state by evaporation
if this cannot be done then it is a reaction
pros of pharmaceutical solutions
Liquids easier to swallow more acceptable by paediatric and geriatric pts
Faster therapeutic response
Uniform distribution of drug through out the preparation, c.f.suspensions andemulsions.
Reduced irritation to the gastric mucosa
Classification of solutions based on solvent polarity
aqueous and non aqueous
advantages of aqueous solutions
Lack of toxicity
Non-expensive
Physiological compatibility
disadvantages of aqueous solutions
could cause hydrolysis of some drugs
has to do with dissolution
why is the maximum level of solubility pharmaceutically important
because it dictates the rate of dissolution
how soluble are the following salts of drugs in water? and how are their respective solubility determined?
atropine sulfate
codeine phosphate
codeine sulfate
morphine sulfate
phernobarbital sodium
very soluble
freely soluble
sparingly soluble
soluble
freely soluble
determined by measuring the weight of solvent required to dissovle 1 gram of the solute or the drug
why are the salts of drugs typically more soluble than the free base or uncahrged form of the drug itself
due to differences in their chemical properties like different ionization states, different intermolecular forces btn structure and polarity…etc