Solutions

Question 1

Definition of solution

Answer 1

Homogeneous one-phase system consisting of 2 or more compounds

Can be aqueous or non-aqueous

Question 2

What the different quality of water for formulation?

Answer 2

potable water
purified water BP
water for injection BP
water free from carbon dioxide or air

Question 3

What are the various methods employed to increase apparent solubility of compounds in aqueous medium

Answer 3

Cosolvency
pH control
Solubilisation
complexation
chemical modification
particle size control

Question 4

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

Answer 4

cosolvency

Question 5

Why does the solubility change with pH?

Answer 5

Degree of ionisation can affect solubility of the drug. The more ionised species there are, the better the solubility of the drug.

Question 6

How is solubilisation achieved?

Answer 6

Addition of a surfactant above the critical micellar concentration.

Large excess of surfactants can make the drug toxic.

Question 7

Factors that affect the choice of solubilising agents?

Answer 7

toxicity and irritancy
miscibility with solvent system
compatibility with other components
odour and taste

Question 8

Which types of alcohols are for external use only?

Answer 8

Industrial methylated spirit (ethanol with 5% methanol as denaturant)
isopropanol

Question 9

Is ethanol able to be used for internal, external use or both?

Answer 9

both

Question 10

Which polyhydric alcohols can be used for both internal and external preparations?

Answer 10

Glycerol, propylene glycol and polyethylene glycols of low MW

Question 11

Which polyhydric alcohol cannot be used for internal preparations due to toxicity

Answer 11

Dipropylene glycol, diethylene glycol, ethylene glycol.

Question 12

What is liquid paraffin classified under, and can what types of preparations can it be used for?

Answer 12

mineral oils

internal and external
emulsions

Question 13

Why is vegetable oil preferred over mineral oil?

Answer 13

Due to the oiliness and tacky nature of mineral oils.

Question 14

True or False: These are only for external use
Xylene
Ethyl ether
isopropyl myristate, isopropyl palmitate
dimethylsulphoxide, dimethylformamide, dimethylacetamide
kerosene

Answer 14

True

Question 15

What are common additives in pharmaceutical preparations?

Answer 15

buffers
colours
sweetening agents 
flavours and fragrances
preservatives
antioxidants
isotonicity modifiers
density modifiers

Question 16

Use of buffer?

Answer 16

resist any change in pH when an acid or alkali is added to the solution.

good for injections, eye drops and nasal drops.

Question 17

Difference between natural and synthetic colours

Answer 17

Natural colours are less stable than synthetic colours

Natural colours are more widely accepted

Synthetic colours are brighter.

Question 18

What is a disadvantage of artificial sweetener?

Answer 18

Tendency to impart bitter or metallic after-taste

Question 19

One example of density modifiers for solutions.

Answer 19

For spinal anaesthetics

Question 20

How are pharmaceutical solutions evaluated for quality?

Answer 20

For all preparations: Drug content
Density, tonicity, viscosity, clarity/particulate matter, colour, sterility

Tonicity is important for large volume infusion.

Question 21

How are pharmaceutical solutions manufactured?

Answer 21

Easiest, use propeller, turbine or paddle mixers

Viscous mixtures use turbine and paddle better.

Question 22

How to determine the maximum drug concentration for a certain amount of surfactant?

Answer 22

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.

Question 23

How to determine the minimum surfactant concentration required to solubilise a certain drug?

Answer 23

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.

Question 24

How does complexation increase apparent solubility of compounds?

Answer 24

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.

Question 25

How does chemical modification increase apparent solubility of compounds?

Answer 25

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.

Question 26

How does particle size reduction increase apparent solubility of compounds

Answer 26

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

Question 27

What are examples of solvents of non-aqueous solutions, and what are they commonly used for?

Answer 27

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)

Question 28

Examples of fixed oils of vegetable origin?

Answer 28

Almond, arachis, olive, corn, soya, castor, cottonseed, sesame, coconut oil.

Question 29

Tasteless and odourless fixed oils are used for _____ preparations?

Answer 29

oral