RVW--1-50

2 Benzyl alcohol is classified as a preservative.  Preservatives prevent the growth of microorganisms and prevent deterioration of pharmaceutical DFs.  

• The ideal preservative must have the following characteristics:
• --effective against a broad spectrum of microorganisms
• --stable for the lifetime of the product
• --nontoxic
• --soluble
• --palatable in taste and odor
• --compatible with other ingredients in the formulation

• Commonly used preservatives:
• --phenol
• --benzyl alcohol
• --thimerosal
• --cresol
• --benzoic acid
• --chlorobutanol
• --benzalkonium
• --cetylpyridinium

3 Cold cream is an example of W/O emulsion.  it is a biphasic liquid DF in which the dispersed phase and the dispersion medium are liquids.  

• Emulsions are classified by five different categories:
• --W/O:  Oil is the continuous phase and water is the dispersed phase i.e. lotions and liniments
• --O/W:  Water is the continuous phase and oil is the dispersed phase i.e. most oral emulsions to mask oily taste of medication
• --Microemulsion:  Unlike emulsions, microemulsions are transparent with a small particle size.  It is believed to be thermodynamically unstable.  The particle size of microemulsion lies between 10 to 200 nm.  It is generally used for the solubilization of the drug in pharmaceutical dosage form.
• --Nanoparticles:  As the name suggests, the particle size of this kind of emulsion is limited to nanograms.  They are useful for the preparation of globulins and toxoids.  Tetanus toxoid and human IgG are examples of nanoparticle emulsions.
• --Multiple emulsions:  W/O/W or O/W/O.  The W/O/W emulsions are generally more preferable in the preparation of pharmaceutical DFs.  They are used to prolong the duration of action of various drugs, to localize a drug in the body, and to prepare cosmetics.

1 Egg yolk or egg white is useful as an emulsifying agent.  It lowers the interfacial tension between the dispersed phase and dispersion medium.  It can be classified as natural or synthetic.

• Commonly used emulsifying agents:
• --Acacia
• --Gelatin
• --Pectin
• --Spans
• --Tweens
• --SLS
• --Tragacanth
• --Methylcellulose
• --Agar

3 The transfer of a drug from a high concentrated area to a low concentrated area is defined as diffusion.

The addition of a levigating agent into a solid to blend to make a paste is defined as levigation i.e. the addition of glycerine to the sulfa powder.

2 The most suitable route for administration of insulin is SC since it has been found that absorption of insulin via this route is slow and therefore the chance of acute hypoglycemia is very rare.

2 The Noyes-Whitney equation helps to find the rate of dissolution of a drug.  The rate of dissolution is a rate-limiting step in the drug's bioavailability.