PRESERVATIVES
A biodegradable, broad- spectrum antibacterial
Anna Gripp, Christine Abbastante - Vertellus
When it comes to formulating personal care products, it is critical to select the most effective anti-bacterial agent. Especially when it comes to preservation, no single preservative is equally effective against all types of microorganisms. Cetylpyridinium chloride (CPC, Figure 1)
is a quaternary ammonium compound that a literature search shows to be biodegradable and which offers effectiveness against many organisms. In the US, it may be used as a preservative and the FDA lists it as an antimicrobial agent. Outside the US, it may be used as an antibacterial agent. CPC has also been used widely in in over-the-counter products including mouthwash, throat lozenges, generally at 0.1-0.2%, nasal sprays and antiseptic (first aid) creams and lotions. Vertellus offers CPC in two forms: powder
and liquid. The trade name for the liquid form is ‘Freshstat™ Cetylpyridinium Chloride’ and it is a 40% CPC in propylene glycol solution. This form provides formulation ease and production flexibility. Our CPC is made in the USA, comes in US and European Pharmacopeia forms, and also in technical grades.
TABLE 1: CPC MICROORGANISM ACTIVITY Class
Active
Parabens Phenolic
Formaldehyde donors Isothiazolinones Halogenated
Acids Quats
Methyl, Ethyl, Propyl, Butyl Phenoxyethanol DMDM Hydantoin Imidazolidinyl urea Diazolidinyl urea MIT
MCT IPBC
Chlorphenesin
Benzoic, Sorbic, Dehyroacetic BAK CPC
TABLE 2: LOG REDUCTION OF BACTERIA USING CPC Odour-causing bacteria
Corynebacterium jeikeium Corynebacterium xerosis
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√/- √ √ √ √ √ - -
√/- √ √
0.38% of 40% CPC in propylene glycol in a deo gel stick
>99.9% >99.9%
Anti-microbial activity CPC is effective against common gram- positive bacteria, including many types of Staphylococci and Streptococci, notably the pathogens Staphylcococcus aureus and Streptococcus pyogenes.1,2,3,4
It is also
reported be to be effective against Listeria monocytogenes in food products. As a general rule, actively-growing
Figure 1: Structure of CPC Based on common knowledge of commonly
used preservatives, Table 1 compares a 40% CPC solution in propylene glycol to a variety of commonly used preservatives, i.e. methylparaben, ethyl paraben, propylparaben, butylparaben, phenoxyethanol, imidazolidinyl urea and chlorphenesin. This shows that CPC is effective over a broad pH range and exhibits broad anti-microbial efficacy against gram- positive and gram-negative bacteria, broad spectrum activity, where the others have activity against fewer of these microorganisms.
Efficacy Bacteria
Gram + √
Gram - -
√ √ √ √ √ √ - -
√/- √/- √
Yeast √
- - -
√/- - √ √ √ √ √ √
Fungi
Mold √
- - -
√/- - √ √ √ √ √ √
0.5% of 40% CPC in propylene glycol in a deo roll-on
>99.9% >99.9%
gram-positive bacterial cells are sensitive to CPC and are rapidly killed (bactericidal effect) at relatively low concentration (at around 15 mg/L). The literature also suggest that gram-positive bacteria may be inhibited (bacteriostatic effect) at even lower concentrations of CPC. CPC is effective against mycobacteria when used at high concentrations. Mycobacteria are relatively insensitive to the effects of most quaternary ammonium compounds, including CPC. This specialised group of gram-positive bacteria – including the pathogens responsible for tuberculosis and leprosy – has cells with tough, waxy walls which make them more difficult to inactivate.2,6,7 In addition, CPC and similar quaternary ammonium compounds can be highly effective in preventing the growth of bacterial spores. It is sporistatic rather than sporicidal since it inhibits the outgrowth of the bacterial spore during germination.8 CPC is somewhat less effective against
common gram-negative bacteria than it is against gram-positive bacteria. For most gram-negative bacteria, the amount required is an average of 25 mg/L.1,2,3
A notable
exception is Pseudomonas, a common aquatic environmental bacterium which is especially insensitive to the effects of CPC, requiring up to 172 mg/L to provide a lethal concentration.2,13,14 It is generally recognised that gram-negative
bacteria are moderately sensitive to quaternary ammonium compounds, including CPC.6
Their
effectiveness can be increased by the use of a chelating agent such as EDTA.9 CPC is also effective against other microbes, mostly yeast-like and filamentous fungi.1,10
It is
typically effective at a use level of approximately 14 mg/L, the anti-fungal effects of quaternary ammonium compounds such as CPC are generally regarded as fungistatic. It is generally accepted that CPC, like
other quaternary ammonium compounds, is less effective against viruses without an outer envelope (bacteriophage F116 and
February 2022 PERSONAL CARE
39
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