Water for injection (wfi) and Types of Water for injection(wfi)
Water is a universal solvent and is used as a vehicle in many pharmaceutical preparations due to following reasons
1.Easy to administer
2.Well tolerated by body
3.Considered as safe vehicle in use
Normal water contains microbes , electrolytes (reacts with the medicament), particulate matter,carbondioxide and cholrine gases in dissolved form .Hence , It cannot be used as a vehicle for parenteral preparations as it causes the contamination of parenteral preparations.
To avoid this problem water which is free from all these contaminants is used.This pyrogen free distilled water is termed as Water For Injection (wfi).It need not be sterile but it must be pyrogen free.
Types of Water for Injection(wfi)
Various types of Water for Injection(wfi) are as follows-1.Bacteriostatic Water for Injection.
This is sterile water which is pyrogen free and contains one or more antimicrobial agents.This water is not used in preparation of large volume parenterals as bacteriostatic agent present may become toxic .Hence,Used in preparation of small volume parenterals.
It should not be packed in containers larger than 30ml capacity.
2.Sterile Water for Injection.
This is distilled water which is free from pyrogens and does not contain any bacteriostatic agent or additives in it.It contains leached out glass constituents during sterilization and storage in glass lined containers.
Sterile Water for Injection is used as vehicle , solvent ,diluents for reconstitution of already sterilized or packaged parenteral preparations.
3.Water for injection free from dissolved air.
Many drugs are sensitive to air and may undergo oxidation when they come in contact with the air.This effects stability of the compound.To avoid this issue it is mandatory to make water for injection free from dissolved air. This is achieved by boiling it for 10 minutes .The space present above the drug solution in container is replaced with inert gas(Example:Nitrogen N2)
4.Water for injection free from carbondioxide (CO2 ).
Sulfonamides and Barbiturates are slightly soluble in water due to their weak acidic nature.Their salt forms have more solubility in water .When these salt form are dissolved in Water for injection containing dissolved carbondioxide it causes drug precipitation.Hence to avoid this issue water for injection must be free from carbondioxide.
This is achieved by boiling water for injection for 10 minutes and it is filled in well sealed containers.
Authored by
S.M.Imroz , M.Pharm (Pharmaceutics).,
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