3. LEARNING OBJECTIVES
At the end of this topic, students will be able to:
Define Preservatives.
List the criteria for selecting a suitable preservative.
Classify preservatives as antimicrobial and
antioxidants.
Discuss the properties of alcohol, Acids, Esters &
Quaternary Ammonium compounds as preservatives.
4. Preservatives
Preservatives are substances that are commonly
added to various foods and pharmaceutical products in
order to prolong their shelf life.
The addition of preservatives to such products,
especially to those that have higher water content, is
essential for avoiding alteration and degradation by
microorganisms during storage.
5. Microbes will grow in an
aqueous solution.
Therefore, it is necessary
that formulator should add
a preservative to the
product to decrease the
probability of product
contamination.
6. SELECTION OF PRESERVATIVE
The major criteria that should be considered in
selecting a preservative are as follows:
1- Effective against a wide spectrum of
microorganisms.
2- Stable for the shelf life of the formulation.
3- Nontoxic.
4- Non-sensitizing.
5- Relatively free of taste and odour.
6- should not be Adsorbed on to the container
7- should be compatible with other formulation
additives.
8- Its efficacy should not be decreased by pH.
8. Antimicrobial preservatives
Antimicrobial preservatives are
included in the preparations to kill or
to inhibit the growth of micro-
organisms inadvertently introduced
during manufacture or use.
They are used in sterile
preparations such as eye drops and
multidose injections to maintain
sterility during use.
9. They may be also added to aqueous
injections that cannot be sterilized in
their final containers and have to be
prepared using aseptic precautions.
Preservatives are also used in
cosmetics, foods, and non sterile
pharmaceutical products such as oral
liquids and creams to prevent
microbial spoilage.
10. Antimicrobial preservatives are classified into two main
sub-groups:
Anti-fungal preservatives.
Anti-bacterial preservatives.
11. ANTI-FUNGAL PRESERVATIVES
Anti-fungal preservatives include compounds such as
benzoic acid, ascorbic acids and their salts.
phenolic compounds, methyl, ethyl, propyl and butyl p-
hydroxybenzoate (parabens).
13. Antioxidants
Antioxidants are included in the pharmaceutical products
to prevent deterioration from oxidation.
Examples
ascorbic acid
citric acid
potassium and sodium salts of sulphurous acid.
14. Types
Preservatives may be grouped into a number of classes
depending upon their molecular structure, including:
Alcohols
Acids
Esters
Quaternary Ammonium compounds
15. 1) Alcohols
Ethanol is useful as a preservative when it is
used as a solvent; however, its dose need a
relatively high concentration to be effective.
13-50%
16. 1) Alcohols
Propylene glycol is also used as a solvent in
oral solutions and topical preparations, and it
can function as a preservative in the range of
15 to 30%.
17. 1) Alcohols
Chlorobutanol and phenylethyl alcohol are
used in lower concentrations of about 1% for
preservative action.
18. 2) Acids
Benzoic acid has a low solubility in water. (1 g/300
mL) of water
0.1 to 0.5%.
Benzoic acid/sodium benzoate is ineffective in solutions
with a pH above 5.
Benzoic acid/sodium benzoate is widely used as a
preservative, especially in foods. It has most of the
properties of an ideal preservative. Its biggest drawback
is the pH dependence of its effectiveness.
19. 2) Acids
Sorbic acid has also a low solubility in water. (1 g/400
mL) at 30°
Patassium sorbate
Sorbic acid is widely used as a preservative in food in
conc. of 0.05 to 0.2%.
20. 3) Esters
Parabens are esters of p-hydroxybenzoic acid and
include the methyl, ethyl, propyl and butyl derivatives.
These compounds are used widely in Pharmaceutical
products and are effective and stable over a pH range of
4 to 8.
0.2%
21. Parabens
Sometimes used in combination to exhibit a wide
spectrum of activity.
The most widely used preservatives are mixture of
Methyl parahydroxybezoate in a 0.2% concentration and
Propyl parahydroxybenzoate in a 0.02% concentration.
They are suitable for both external and internal use.
22. 4) Quaternary Ammonium compounds
Benzalkonium chloride is used at relatively low
concentration, 0.002 to 0.02%, depending on the nature
of the pharmaceutical product.
This class of compounds has an optimal activity over the
pH range of 4 to 10 and is quite stable at room
temperature.
It is used generally in preparations for external use or those
solutions that come in contact with mucous membranes.
