Preservatives are chemical substances used to prevent microbial growth and increase the shelf life of drugs and cosmetics. They work by inhibiting microbial growth through various mechanisms like acting as antioxidants, antimicrobial agents, or chelating agents. The effectiveness of preservatives can be influenced by factors like pH, concentration, microbial susceptibility, interference from other ingredients, and interaction with solid particles. Common preservatives include parabens, benzoic acid, sodium benzoate, and phenoxyethanol which are used in pharmaceutical and cosmetic products to inhibit bacteria, molds, and yeasts.

1. PRESERVATIVES
MISS. RUCHITA RAVINDRA BHAGWAT.
M.PHARM FIRST YEAR
PHARMACEUTICS

2. DEFINITION
A chemical substance used to
preserve organic substance from
decay or spoilage by preventing
microbial attack .
 Preservatives are the chemical
substances used to improve or
amplify shelf life of drugs by
decreasing or lowering the oxidation
of active and Excipients and by
reducing microbial production

3. NEEDS FOR PRESERVATIVES
 To protect our drug from microbial
attack .
 To enhance activity and efficacy of
drug .
 To increase shelf life of our product .
 To stabilize our product.
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4. MERITS-
Prevent the bacterial growth, spoilage.
Keeps the product fresh for longer time.
Improves the appearance of cosmetic
product.
Combination of esters exhibit increased
activity.
DEMERITS-
Can be toxic in larger concentration.
Sometimes interact with the formulation.
Incompatible with some proteins
Some non-ionic emulsifiers reduce the
activity.
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MECHANISM OF
ACTION
ANTIOXIDANTS
ANTIMICROBIAL AGENTS
CHELATING AGENTS
SOURCE
NATURALLY OBTAINED
SYNTHETICALLY
PREPARED

6. ANTI-OXIDANTS:
Anti oxidants are used to reduced the
oxidation of active compound and excipients
due to formation of free radicals by using their
self reducing activity in finished product .
TYPES OFANTIOXIDANTS
 TRUE ANTIOXIDANTS
 REDUCING AGENT
 ANTIOXIDANTS SYNERGISTS

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TRUE
ANTIOXIDANTS
REDUCING
AGENT
ANTIOXIDANTS
SYNERGISTS
• These are thought to block chain
reactions by reacting with free
radicals.
• Example- Butylated
hydroxytoluene
• These have a lower redox
potential than the drug or
excipients they are protecting
• Example- Ascorbic acid
• These enhance the effect of
antioxidants
• Example- Sodium edetate

8. ANTI-MICROBIAL PRESERVATIVES
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 It is added in product to minimize risk of spoilage and to kill low levels of
contaminants introduced during storage or repeated use of a multi-dose container .
 These agents mainly work by inhibiting the cell wall, cell membrane growth or other
bacterial organelles which may attack our product.
PREPARATIONS REQUIRED ANTI- MICROBIAL PRESERVATIVES:
Preparations which contain water are at risk of microbial spoilage such as:
 Solutions
 Suspensions
 Emulsions
 Topical preparation e.g creams
 Injectable
 Eye drops etc

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EXAMPLES-
BENZOIC ACID
It is used as a food preservative It inhibits the growth of microbes including mould, yeast and some
bacteria. Used as antiseptic also
METHYLPARABENS
It is a white crystalline powder, characteristic odor, freely soluble in water and alcohol It is used as
antiseptic and preservative in various pharmaceutical preparations. It is also used in cosmetic
preparations susceptible to decomposition.
SODIUM BENZOATE:
It is a white crystalline solid, soluble in water and alcohol It is used extensively as food and
pharmaceutical preservatives. It is not a bactericidal, only a bacterio- static agent along with
fungistatic activity
ALCOHOLS -CHLORO BUTANOL:
It is used as preservative and bacterio-static agent.
MERCURIAL COMPOUNDS
PHENYLMERCURIC NITRATE: It is used as bacterial preservative in pharmaceutical preparation
and also used as topical antiseptic.

10. CHELATING AGENTS
Chelating agents act as preservatives and
protect product by forming complex with
it preventing its deterioration.
Examples include:
 EDTA
Citric acid etc
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11. NATURAL PRESERVATIVES
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These drugs are obtained by natural sources that is plant, mineral sources, animal
etc.
Examples-Neem oil ,salt (sodium chloride),Lemon, Honey.
ARTIFICIAL PRESERVATIVES
These preservatives are man made by chemical synthesis active against by various
micro-organism in small concentration .
Examples-Benzoates, Sorbates,Propionets,Nitrates.

12. A. Dissociation and Ph
B. Concentration
C. Susceptibility of organisms
D. Interference by ingredients of
cosmetics
E. Influence of solid particles
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FACTORS AFFECTING
MICROBIAL
PRESERVATIVE EFFICACY

13. DISSOCIATION AND PH
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 An ideal preservative should be effective in wide range of pH. However, in practice,
majority of preservatives are active in acidic range than in alkaline range.
 Preservatives which are active in both acidic and alkaline pH ranges have the disadvantage
of being highly reactive in nature. For example, formaldehyde and formaldehyde releasing
compounds. These compounds can react with other ingredients of formulation.
 There are many preservatives which are greatly influenced by pH. For example, weak
acids.
 Activity of weak acids depend on their undissociated amount of acid which in turn
depends on the dissociation constant and pH of the system.
 Simon has demonstrated that effectiveness of weak acids is influenced in a regular manner
by changes in pH.
 On the other hand, there are preservatives which are active only in dissociated from. For
example, cationics.
 Quaternary ammonium compounds are effective in higher pH (alkaline) but these become
ineffective in lower pH (acidic).
 Some preservatives may be pH dependent because of the stability problem. For example,
2-nitro-2-bromo-propanediol(Bronopol) start deteriorating at pH higher than 7.

14. CONCENTRATION
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Some materials used in cosmetic formulations have antimicrobial action and,
therefore, concentration of preservatives required may be very less.
There may be ingredients in cosmetics which promote growth of micro-
organisms, for example, mucilages of natural gums. Concentration of
preservatives, obviously will be more in such products.
Recommended effective concentration range from as little as 0.001% (organic
mercury compounds) to 0.5-1.0% (weak acids).
Availability of preservatives to micro-organisms is more important than
overall concentration of preservatives which may depend upon permeability
across cell wall, diffusion rate, and degree of absorption and partition
coefficient of the preservative depending on the mechanism of action.
Concentration of preservatives may be reduced if more than one preservative
is used in combination.

15. SUSCEPTIBILITY OF ORGANISMS
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 Hydroxy benzoates are active against moulds, fungi and yeasts but less active against bacteria.
 Chlorobutanol has antibacterial and anti-fungal activities.
 Phenyl mercuric nitrate is active against bacteria, fungi, moulds and yeasts.
INTERFERENCE BY INGREDIENTS OF COSMETICS
Several non-ionic surfactants such as Tween 80,Polyethylene glycol 1000 monocetyl ether,
Polyethylene glycol400 laurate interfere with activity of preservatives by exerting protective effect
on micro- organisms..
Soaps and anionic surfactants in lower concentrations promote growth of Gram-negative bacteria.
Hydrophilic polymers like polyethylene glycols, gum tragacanth, methyl cellulose, carboxy-methyl
cellulose and polyvinyl-pyrolidone have only marginal effect in reducing efficiency of majority of
anti- microbials.
 Addition of certain materials to the aqueous phase of emulsions help in minimizing adverse effect
of non-ionic surfactants on preservatives.
Materials like propylene glycol, glycerin and hexylene glycol have been found useful in this respect.

16. INFLUENCE OF
SOLID PARTICLES
Some of the insoluble solid particles
are kaolin, chalk, zinc oxide, talc and
pigments.
Preservatives can be adsorbed on the
surface of solid particles.
The extent of adsorption will depend
on nature of solid particles and pH of
the preparation.
Preservatives can also interact with
plastics.
Phenolic and quaternary ammonium
compounds have been reported to
react with polyurethane.
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