Preservatives

Author:Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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DefinitionThis section has been translated automatically.

Substances used for the preservation of microbially susceptible ointment bases. Although they are not "medicinally active ingredients", they are, according to the prevailing interpretation, "effective other ingredients" of a formulation. Therefore, in contrast to excipients, which do not have a pharmacological effect of their own or do not influence it, they should not be added without the consent of the physician if possible.

Field of application/useThis section has been translated automatically.

Formulations which contain water in their external phase (oil-in-water lotions, oil-in-water creams, water-in-oil lotions, water-in-oil creams, see also creams, lotions) and are intended to be preserved over a longer period of time.

Notice!

Preparations with an alcohol content > 20% are not at risk. Formulations with a low water content (powders, oils or fatty ointments) are only susceptible to germ multiplication if the container is constantly opened.

Notice! Preservatives are common contact allergens (Kathon CG by 4%, benzalkonium chloride, thiomersal and parabens by 2% each), so whenever possible, one should try to do without preservatives (recipe of small amounts, storage in the refrigerator)!

TablesThis section has been translated automatically.

Overview of the most common substances used for the preservation of externals

Preservative

Concentration

Use

Benzoic acid

0,1-0,2%

Benzyl alcohol

1-2% and above

Benzalkonium chloride

0,002-0,02%

especially for eye, nose and ear drops

Chlorbutanol

0.3-0.5% (unstable at pH > 5)

Chlorhexidine diacetate

0,005-0,1%

especially for eye, nose and ear drops

Chlorhexidine digluconate

0,005-0,01%

especially for eye, nose and ear drops

5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-iso-thiazolin-3-one, Kathon CG

mainly cosmetics

Ethanol

> 15%

Glycerol

> 30%

p-Hydroxybenzoic acid methyl ester, nipagine, solbrol

0,06%

ethyl p-hydroxybenzoate

0,07%

p-Hydroxybenzoic acid propyl ester, Nipasol, Solbrol P

0,04%

Imidazolinyl urea, Germall 115

mainly cosmetics

Potassium sorbate

0,1%

Sodium benzoate

0,1-0,2%

Phenoxyethyl alcohol

1-1,5%

phenyl mercury compounds, such as -borate, -nitrate, -acetate

0,002-0,005%

especially for nose and ear drops as well as rectally and vaginally applicable external preparations

1,2-propylene glycol

> 15%

Sorbic acid and its salts

0.1-0.15% (unstable at pH > 5)

Sorbitol

> 70%

Thiomersal

0,002-0,015%

especially for eye, nose and ear drops


Preservative

available concentration [%]

Effectiveness against Gram-positive pathogens

Effectiveness against Gram-negative pathogens

Efficacy against yeasts

Effectiveness against fungi

Chlorbutanol

0,5

very effective

very effective

weakly effective

weakly effective

Benzyl alcohol

1,0

very effective

weakly effective

weakly effective

weakly effective

Phenylethyl alcohol

1,0

very effective

very effective

weakly effective

weakly effective

Phenol, cresol

0,3

very effective

very effective

weakly effective

weakly effective

PHB methyl ester

1,18

very effective

very effective

not effective

not effective

PHB propyl ester

0,02

very effective

very effective

weakly effective

not effective

PHB mixture M + P

0,2

very effective

very effective

weakly effective

weakly effective

PHB mixture M + P + benzyl alcohol

0,2 + 0,5

very effective

very effective

very effective

very effective

Benzoic acid

0.1 (only in the pH 6 range)

not effective

not effective

very effective

very effective

Sorbic acid

0.2 (only in the pH 6 range)

not effective

not effective

very effective

very effective

Chlorhexidine

0,005-0,1

very effective

very effective

weakly effective

weakly effective

Benzalkonium chloride

0,01

very effective

weakly effective

very effective

very effective

Phenylmercurinittate

0,001

very effective

very effective

very effective

very effective

Thiomersal

0,02

very effective

very effective

very effective

very effective


Preservative

Optimal pH range

2

3

4

5

6

7

8

9

10

Chlorbutanol

very effective

very effective

very effective

very effective

not effective

not effective

not effective

not effective

not effective

Benzyl alcohol

very effective

very effective

very effective

very effective

weakly effective

weakly effective

not effective

not effective

not effective

Phenol, cresol, p-chloro-m-cresol

very effective

very effective

very effective

weakly effective

weakly effective

weakly effective

weakly effective

weakly effective

weakly effective

PHB methyl ester

very effective

very effective

very effective

very effective

very effective

weakly effective

weakly effective

weakly effective

not effective

PHB propyl ester

very effective

very effective

very effective

very effective

very effective

weakly effective

weakly effective

weakly effective

not effective

Sodium sulphite

not effective

not effective

not effective

not effective

not effective

very effective

very effective

very effective

not effective

Benzoic acid (pKa value 4.194)

very effective

very effective

very effective

very effective

very effective

not effective

not effective

not effective

not effective

Sorbic acid (pKa value 4,76)

very effective

very effective

very effective

very effective

very effective

not effective

not effective

not effective

not effective

Chlorhexidine

not effective

not effective

not effective

very effective

very effective

very effective

very effective

not effective

not effective

Benzalkonium chloride

not effective

very effective

very effective

very effective

very effective

very effective

very effective

weakly effective

weakly effective

Phenylmercurinitrate

not effective

not effective

not effective

not effective

not effective

very effective

very effective

very effective

very effective

Thiomersal

very effective

very effective

very effective

very effective

very effective

very effective

not effective

not effective

not effective

Phenylethyl alcohol

very effective

very effective

very effective

very effective

very effective

very effective

not effective

not effective

not effective

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Last updated on: 29.10.2020