Pharmaceutical Aids And Necessities - Pharmaceutically Acceptable Glass

The chemistry of glass is extremely complicated.The word "glass" is a generic term referring to vitreous material (material which softens gradually over a temperature range rather than melting sharply).Most commercial glasses are vitreous silicates with some type of additives which confers special properties.Boron decreases the coefficient of expansion in PYREX Glass.Potassium gives a brown light-resistant glass.The rare earths selectively absorb light of certain wavelengths.

Glass may be considered as SODIUM SILICATE (Na₄SiO₄).

Aqueous solutions may slowly become alkaline upon standing for prolonged times in soft glass containers.It is shown by the reaction given below:

4Na⁺ + SiO₄^-4 + 3H₂0 ⟶ H₃SiO₄^- + 4Na⁺ + 3OH^-

The compendia usually specify the type of glass container if the drug is base-sensitive.The water for injection must be stored in glass of TYPE Ⅰ or Ⅱ as the above reaction is greatly speeded up during heat sterilization.Both the U.S.P and N.F. define the same four glass types and their alkalinity limits.

1)TYPE 1 : The TYPE 1 glass to describe is a a highly resistant Borosilicate glass.It is type of powdered glass which is used for buffered and unbuffered solution.

2)TYPE 2 : The Type 2 Glass is TREATED SODA-LIME GLASS.It is a type of water attack glass.Type 2 glass is used for oleaginous solutions,dry powders and buffered aqueous solution with pH below 7.0

3) TYPE 3 : The TYPE 3 Glass is SODA-LIME Glass which is powdered glass and is used for dry powders and oleaginous solutions.

4) TYPE NP : This type of glass to described is general purpose soda lime glass which is also a powdered type.This type of glass is not for parenterals use.It is used for tablets,ointments,oral solution and external liquids.

Certain drugs must be protected from light.There are numerous types of containers - colourless,opaque and coloured available for packing.The opaque container would be superior light-protective containers,but,except for ointments,clear containers are preferred for dispensing,if for no other reason than that the patient likes to see what he/she is buying,the amount left in the bottle and ease of pouring.

There are four types of clear containers available : Colourless,Green,Blue and Amber.Since most light-catalyzed degradation is due to ultraviolet radiation,this is the area of electromagnetic spectrum that must be excluded.For the most part Blue glass does not confer much protection.Green glass may or may not,depending upon the type and intensity of green.Amber glass will usually screen-out ultraviolet radiation very effectively and is usually the colour recommended for protection from light.Both U.S.P and N.F. have identical standard for percent transmission of light in 290 to 450 nm region,dependent upon the thickness of the glass.It is assumed that radiation below 290 has been screened out by atmosphere.