Preservatives Flashcards
Tell me about the Preservative Efficacy Test
A preservative is essential to help prevent microbes (bacteria, mould, and yeast) growing. Preservatives stop growth by acting on spores when they germinate and killing cells (usually by disrupting cell membranes) or by making the product hostile to growth.
Preservative efficacy test to prove the efficacy of the chosen preservative against a number of challenge organisms.
The product is spiked with each of the challenge organisms at a concentration of 103 to 106
Measurements are taken over a period of time - 7, 14, 21 and 28 days, possibly sample periodically throughout the shelf life depending on risk assessment
Challenge organisms include Yeast, Mould, Gram neg, Gram Positive and n objectionable.
Aspergillus brasiliensis - mould, Staph Aureus - people skin Gram positive, Pseudomonas aeruginosa - water Gram negative, Candida Albicans - yeast, E. Coli Gram negative objectionable organism from the gut
Looking for a minimum of a 3 log reduction at 14 days and no regrowth
What is a preservative?
A Preservative is a natural or synthetic compound which inhibits or kills contaminating microorganisms. Preservatives are used in product formulations to prevent “in-use” contamination of the product.
* An Antimicrobial refers to any compound inhibiting or killing all or some microorganisms, but without therapeutic effect.
* Phenols are widely used in household cleaning products as a disinfectant in low concentrations. Phenol is used in mouthwash. Phenol may have been the first surgical antiseptic.
* Bacteriostasis means the agent inhibits bacterial growth without organism destruction. The bacteria is in a stationary phase of growth.
Bactericidal means that the agent kills bacteria.
Ideally a preservative system is
- Acceptable to all Regulatory Authorities
- Kills bacteria rather than reducing numbers
- Effective at low concentrations
- Active against all relevant organisms
- Fast acting
- Chemically stable
- Compatible with excipients and packaging materials
- Colorless and odourless
- Safe
- Present in the aqueous phase
- Cost effective
Basic Expectations of a preservative system are
that it addresses the ideal characteristics of the product, it allows the product to give a true result in the pharmacopeia Preservation Efficacy Test, known as PET, and that it has a toxicity profile suitable for the intended route of administration.
The choice of preservative is also a compromise between
any microbiological activity between the preservative and the expected organism, compatibility with the formulation and pack, as well as long term stability needs. Use of combinations can widen the range of the organisms affected. One preservative may potentiate the effects of another. It is essential to maintain the concentrations of each element of the combined system and to consider any long-term effects such as on expected degradation profiles. Choose the minimum concentration required to inhibit growth which will vary from organism to organism. Compatibility with formulation and pack is critical.
Consideration must be given to whether the preservative system is affected by:
- Any preservatives that are being used in combination
- The aqueous phase of the product
- Adsorption or binding to solids or to the pack, and
- Any effects of excipients
The patient, or user, of multi dose large packs presents a risk of repeatedly contaminating the product each time they use it. This risk can be lowered by reducing the size of the pack or changing the pack itself, for example to small volume tubes.
Preservation Efficacy Testing (PET)
The testing required to confirm non-therapeutic antimicrobial compound effectiveness is not straightforward.
* There is no single test method that distinguishes between the activity required for disinfectant or preservative use of the same compound
* There are millions of types of microorganisms (species, types, variants, serotypes etc.) against which the compound might have to be effective
* Test organisms must be used as homogeneous suspensions of single cells. This is an unnatural state for organisms which are generally found in colonies or clumps
* Use of different media may give different results
* We expect antimicrobials to be effective in many different environments such as the presence of dirt, hard or soft water As a result many tests have been developed in attempts both to “improve” the reliability of the test itself and its relevance to all situations.
PET test method
- Preparation of inocula
- Product inoculation
- Product incubation
- Result interpretation
There key stages of preservative testing are the
- Test Inoculum, and the
- Removal of Anti-microbial Activity
- Dilution
- Neutralization
- Filtration
PET test organisms
The test inoculum is typically performed with a range of organism types, at known number, representing the main flora found in the pharmaceutical production environments, including: Aerobic and anaerobic Gram-positive bacilli, such as Bacillus subtilis or Clostridium sporogenes, as well as Gram-positive cocci skin-type organisms like Staphylococcus aureus. Oxidative and fermentative Gram-negative bacilli typifying water borne or gut organisms – for example Pseudomonas aeruginosa and E coli, Yeasts, such as Candida albicans, and Molds, such as Aspergillus niger. If the antimicrobial preservative system is not entirely bactericidal, the microbiologist will need to assess the extent of the preservative’s ability to kill the microbes, the must first perform the removal of any remaining Antimicrobial Activity in the test sample before attempting to count any possible survivors. This is done through some form of neutralization by using one or a combination of the following techniques: Dilution, Neutralization, and/or Filtration.
