Solutions and solubility
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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
types of water
portable purified water used for injections
portable water
Water freshly drawnfrom the public watersupply (main system)and suitable fordrinking.
purified water
Freshly boiled andcooled immediately before use to destroymicroorganisms
porperties of water used for injections
is sterile CO2-free low electrical conductivity low endotoxins high purity absence of pyrogens…etc
types of pharmaceutical solutions
Solid-in-liquid Liquid-in-liquid Solid-in-solid Gas-in-gas Gas-in-liquid
liquid in liquid solution
A liquid-in-liquid solution is a one-phase molecular dispersion of twoliquids which are MISCIBLE with each other (e.g. ethanol and water).
Solid-in-solid solutions what do solid in solid solutions result to
A solid-in-solid solution is a molecular dispersion of a solid solute ina solid solvent. the formation of a mixed crystal of both components
importance of a solid-in-solid solution
can be used to enhance the dissolution of a poorly soluble drug.