Solutions Flashcards
Definition of solution
Homogeneous one-phase system consisting of 2 or more compounds
Can be aqueous or non-aqueous
What the different quality of water for formulation?
potable water
purified water BP
water for injection BP
water free from carbon dioxide or air
What are the various methods employed to increase apparent solubility of compounds in aqueous medium
Cosolvency pH control Solubilisation complexation chemical modification particle size control
What is the improvement of a weakly soluble substance in water via addition of a water-miscible solvent in which the substance is also soluble
cosolvency
Why does the solubility change with pH?
Degree of ionisation can affect solubility of the drug. The more ionised species there are, the better the solubility of the drug.
How is solubilisation achieved?
Addition of a surfactant above the critical micellar concentration.
Large excess of surfactants can make the drug toxic.
Factors that affect the choice of solubilising agents?
toxicity and irritancy
miscibility with solvent system
compatibility with other components
odour and taste
Which types of alcohols are for external use only?
Industrial methylated spirit (ethanol with 5% methanol as denaturant)
isopropanol
Is ethanol able to be used for internal, external use or both?
both
Which polyhydric alcohols can be used for both internal and external preparations?
Glycerol, propylene glycol and polyethylene glycols of low MW
Which polyhydric alcohol cannot be used for internal preparations due to toxicity
Dipropylene glycol, diethylene glycol, ethylene glycol.
What is liquid paraffin classified under, and can what types of preparations can it be used for?
mineral oils
internal and external
emulsions
Why is vegetable oil preferred over mineral oil?
Due to the oiliness and tacky nature of mineral oils.
True or False: These are only for external use
Xylene
Ethyl ether
isopropyl myristate, isopropyl palmitate
dimethylsulphoxide, dimethylformamide, dimethylacetamide
kerosene
True
What are common additives in pharmaceutical preparations?
buffers colours sweetening agents flavours and fragrances preservatives antioxidants isotonicity modifiers density modifiers
Use of buffer?
resist any change in pH when an acid or alkali is added to the solution.
good for injections, eye drops and nasal drops.
Difference between natural and synthetic colours
Natural colours are less stable than synthetic colours
Natural colours are more widely accepted
Synthetic colours are brighter.
What is a disadvantage of artificial sweetener?
Tendency to impart bitter or metallic after-taste
One example of density modifiers for solutions.
For spinal anaesthetics
How are pharmaceutical solutions evaluated for quality?
For all preparations: Drug content
Density, tonicity, viscosity, clarity/particulate matter, colour, sterility
Tonicity is important for large volume infusion.
How are pharmaceutical solutions manufactured?
Easiest, use propeller, turbine or paddle mixers
Viscous mixtures use turbine and paddle better.
How to determine the maximum drug concentration for a certain amount of surfactant?
Plot the optical density vs drug concentration curve. Vary the amounts of drug added into vials with constant concentration of surfactant.
maximum drug concentration that produces a clear solution is obtained from the graph.
How to determine the minimum surfactant concentration required to solubilise a certain drug?
Find MDC values of different concentrations of surfactants, a plot of MDC vs surfactant concentration is plotted.
Minimum surfactant concentration required to solubilise a certain drug concentration can be determined.
From this plot, we can also determine the critical micellar concentration.
How does complexation increase apparent solubility of compounds?
involves the interaction of a poorly soluble drug with a soluble material to form a soluble complex.
Complex formation should be easily reversible as most complexes are macromolecules which tend to be inactive.
How does chemical modification increase apparent solubility of compounds?
Synthesising soluble salts of the drug can help allow better dissolution. The salt can easily dissociate into the ions in aqueous solution.
i.e sodium succinate salt of chloramphenicol.
How does particle size reduction increase apparent solubility of compounds
Size and shape of very small particles < 1 micron can affect the solubility.
size reduction usually done via milling. This method is less commonly employed to improve solubility
What are examples of solvents of non-aqueous solutions, and what are they commonly used for?
Fixed oils of vegetable origin, alcohols, polyhydric alcohols, mineral oils
They are usually used for drugs that are unstable in water and used to prepare intramuscular injection of drugs for depot therapy (used for suspension as well)
Examples of fixed oils of vegetable origin?
Almond, arachis, olive, corn, soya, castor, cottonseed, sesame, coconut oil.
Tasteless and odourless fixed oils are used for _____ preparations?
oral
