Preservatives preservative efficacy

The parabens are effective over a wide pH range and have a broad spectrum of antimicrobial activity, although they are most effective against yeasts and molds. Antimicrobial activity increases as the chain length of the alkyl moiety is increased, but aqueous solubility decreases therefore a mixture of parabens is frequently used to provide effective preservation. Preservative efficacy is also improved by the addition of propylene glycol (2-5%), or by using parabens in combination with other antimicrobial agents such as imidurea see Section 10. 

In view of these potentials for major reductions in preservative efficacy, considerable effort has gone into attempts to devise equations in which one might substitute variously derived system parameters such as partition coefficients, surfactant and polymer binding constants and oil water ratios in order to obtain estimates of residual preservative levels in aqueous phases. Although some modestly successful predictions have been obtained for very simple laboratory systems, they have proved of limited practical value as data for many of the required parameters are unavailable for technical grade ingredients or for the more complex commercial systems. 

The formulation scientist must be aware of interactions between preservatives and other components of a formulation that could compromise the efficacy of the preservative. For example, proteins can bind thi-merosal, reducing preservative efficacy. Partitioning of preservative into a micellar phase or an oil phase (in an emulsion) can also reduce the effective concentration of preservative available for bactericidal or bacteriostatic action. Preservative efficacy testing should be done on the proposed formulation to assure an effective preservative concentration. 

Since the organic mercurials offer an alternative to quaternary ammonium preservatives, and since preservative efficacy of ophthalmic solutions is essential, the choice among these alternatives should be based on a benefit-to-risk analysis as long as a ban is not imposed on the use of these organometallic preservatives. 

Surfactants. The use of surfactants is greatly restricted in formulating ophthalmic solutions. The order of surfactant toxicity is anionic > cationic >> nonionic. Several nonionic surfactants are used in relatively low concentrations to aid in dispersing steroids in suspensions and to achieve or to improve solution clarity. Those principally used are the sorbitan ether esters of oleic acid (Polysorbate or Tween 20 and 80), polymers of oxyethylated octyl phenol (Tyloxapol), and polyoxyl 40 stearate. The lowest concentration possible is used to perform the desired function. Their effect on preservative efficacy and their possible binding by macromolecules must be taken into account, as well as their effect on ocular irritation. The use of surfactants as cosolvents for an ophthalmic solution of chloramphenicol has been described [271]. This com-... 

The choice of the excipients and their concentration, including their function (e.g., antimicrobial preservatives, antioxidants. ..). In the case of antimicrobial preservatives, data are expected on the preservative efficacy in products on storage, including after reconstitution or dilution and during the period of use. 

Where a large pack size is provided, it might be necessary to undertake more extensive in-use testing and/ or to restrict the in-use shelf life once the container has been opened. In addition to preservative efficacy testing the chemical stability of antimicrobial preservatives should also be investigated over the unopened and in-use shelf lives of the product. 

Where antioxidants or antimicrobial preservatives are used, the finished product release specification will need to include identification tests and assays for these two types of excipient. The shelf life specification should also include a specification for assay for antimicrobial preservatives. Stability data will be required for both antioxidants and antimicrobial preservatives in the finished product, and in addition the preservative efficacy of the formulated product should be examined over its shelf life and by means of appropriate in-use stability tests. Preservative efficacy data should also be presented at the lower limit of the preservative assay. 

Aqueous products that are at greatest risk from microbial spoilage include solutions, suspensions, and emulsions for repeated oral, parenteral, or external use and include critical products such as multidose injections and eye drops. Unpreserved products without adequate antimicrobial efficacy should not be presented in containers intended for use on more than one occasion unless justified. When antimicrobial preservatives are used, their efficacy has to be demonstrated using the Ph Eur test for antimicrobial preservative efficacy. Factors to be taken into account in designing a preserved product include the nature of the preservative, its concentration in the product, the... 

The preservation efficacy aspects of parenteral products are particularly important for those products that are permitted to contain preservatives. This is not allowed for large-volume injections or for any product gaining access to the cerebrospinal fluid or for intra- or retro-ocular injection (according to the Ph Eur). Unpreserved products should be labeled to state this unequivocally. 

The availability of unpreserved and preserved dosage forms is considered. Mention is made of formulation changes necessitated by multidose products. The need for adequate antimicrobial preservative efficacy can be discussed if this was an issue during product development. 

Chemical products should be designed to preserve efficacy of function while reducing toxicity. 

Storage and preparation of polyclonal and monoclonal antibodies are very important for successful immunostaining. When a new antibody arrives in a laboratory, special attention should be paid to its storage instructions and optimal temperature. Detailed records of arrival and expiry dates, and whether it needs to be aliquoted to maintain efficacy by avoiding ffeeze-thaw effects, should be kept. Attention to these details will preserve the efficacy of the antibody and its shelf hfe, prevent damaging freeze-thaw cycles, and will make optimization of the immunohistochemical procedures easier, ft is often necessary to aliquot antibodies, especially when storage below 4°C is required. 

A stability-indicating presrvative assay can be justified only at all time intervals as a substitute for the USP Antimicrobial Effectiveness Test by confirming preservative efficacy at 50, 75, and 100% of the lower shelf-life specification. 

A sample of a standard calcium carbonate slurry was received from a large manufacturer in the USA. This sample was subjected to preservative efficacy testing according to the ASTM E 723-91 test protocol. Preservative treated samples were inoculated with a mixed bacterial inoculum containing organisms with a known tolerance or resistance to BIT (l,2-Benzisothiazolin-3-one). Untreated controls were included for reference purposes. The test procedure is outlined below. 

Figure 2 Preservative efficacy of Bronopol in a calcium carbonate slurry using the ASTM E723-91 test procedure...

Figure 6 Preservative efficacy of Bronopol and DBDCB alone and in combination in a water-based paint using a multiple challenge test procedure...

The main objective of validation of an analytical procedure is to demonstrate that the procedure is suitable for its intended purpose. The procedures presented in this SOP provide basic guidelines for the validation of methods for microbiological assay, estimation of the number of microorganisms, detection of indicators of objectionable microorganisms, validation of preservative efficacy testing, and validation of the sterility testing and endotoxin test (LAL test). 

The objective is to provide standard procedure for performing the preservative efficacy test for nonsterile and sterile dosage forms. 

Product categories under preservative efficacy test (Table 1) Table 1 Product Categories... 

Media perform growth promotion test for all media used in preservative efficacy test... 

Parabens are approved for use in oral solution and suspensions at a concentration of 0.015% to 0.2% w/v. Due to their low solubility, the sodium salts of parabens are often used in aqueous formulations. The parabens are most effective in the pH range of 2 to 6, and their antimicrobial activity decreases with increasing pH. Additionally, they are very unstable at pH 8 or above in solution. Methyl paraben has also demonstrated incompatibility with sorbitol and may show some discoloration in the presence of iron. The absorption of methylparaben by plastics has been reported with the amount absorbed being dependent upon the type of plastic and vehicle. However, no absorption has been reported for low density polyethylene (LDPE) or high density polyethylene (HDPE) containers. Certain coloring agents such as yellow iron oxide, ultramarine blue, and aluminum silicate can extensively absorb ethyl paraben in simple aqueous systems, thus reducing its preservative efficacy. 

Akers MJ, Boand AV, Binkley DA. Preformulation method for parenteral preservative efficacy evaluation. J Pharm Sci 1984(Jul) 73(7) 903-905. 

Nguyen NAT, Wells ML, Cooper DC. Identification of factors affecting preservative efficacy and chemical stability of lamivudine oral solution through statistical experimental design. Drug Dev Ind Pharm 1995 21 1671-1682. 

Any differences between the release and shelf-life acceptance criteria for antimicrobial preservatives should be supported by the results of preservative efficacy testing. 

Preservative efficacy testing Preparation, review, approval, and revision... 

With drug products containing preservatives, the stability protocol should include preservative efficacy testing. Microbial challenge testing should be conducted at appropriate intervals—at least once a year unless significant losses are observed earlier as a result of assay procedures. 

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