Tests with antimicrobial formulations

Tests with antimicrobial formulations containing Triclosan ... 

Microbiological protection of multiple-dose presentations such as liquid inhalations, nasal sprays, oral liquids, creams, and lotions is more complex. Once opened they are susceptible to microbiological contamination. If they are aqueous-based, they are in principle susceptible to proliferation of these new contaminants. To avoid this, they are formulated with antimicrobial agents or preservatives and are expected to be able to comply with preservative efficacy standards specified in the pharmacopeias. Preservative efficacy tests (not harmonized) are described in Section 51 of the USP and Section VIII. 14 of the PhEur (Fig. 3). 

Example 2.10 Suppose the researcher exposed agar plates inoculated with Escherichia coli to forearms of human subjects that are treated with an antimicrobial formulation, as in an agar-patch test. In the study, four plates were attached to each of the treated forearms of each subject. In addition, (me inoculated plate was attached to untreated skin on each forearm to provide baseline determinations of the initial microbial population exposure. A random selection schema was used to determine the order in which the plates would be removed from the treated forearms. Two plates were removed and incubated after a 15 min exposure to the antimicrobially treated forearms, two were removed and incubated after a 30 min exposure, two were removed and incubated after a 45 min exposure, and the remaining two after a 60 min exposure. Two test groups of five subjects each were used, one for antimicrobial product A and the other for antimicrobial prcxluct B, for a total of 10 subjects. The agar plates were removed from 24 h of incubation at 35°C 2°C, and the colonies were counted. The duplicate plates at each time point for each subject were averaged to provide one value for each subject at each time. 

The selection of the preservative system for multiuse new products is the responsibility of the R D formulation group. Typical shelf specifications are 80 to 120% of label specifications. The appropriate preservative system for the particular formulation should be demonstrated to be effective by microbial challenge to at least 75% and preferably 50% of the target concentration. It is recommended that during development the product be formulated with preservative concentrations of 100, 75, and 50% of the labeled amount and be subjected to antimicrobial effectiveness testing to determine the lowest effective preservative concentration. 

Patents have been granted for innovations involving the preparation and activities of broad-spectrum antimicrobial emulsions from 1977 (Sippos) to 2000 (Baker). All of these patents claim antibacterial activity, but all involve additives in the non-aqueous phase of the emulsion that are known to be antibacterial alone and before emulsification. Wide spectrum applications for these nanoemulsions have been claimed with positive results for bacteria, fungi, and viruses. The term nanoemulsion is used in US patents discussed below, but the generic term for the product of an emulsification (Gooch 2002, 1980) of a liquid within a liquid is an emulsion. United States patents 6,015,832 and 5,547,677 were examined and formulations in key claim statements were reproduced, and tested using standard methods for effectiveness. Additional patents listed in the reference section were reviewed as part of this study. 

Preservatives should not usually be included in parenteral formulations except where a multidose product is being developed. The Committee for Proprietary Medicinal Products (CPMP) Notes for Guidance on Inclusion of Antioxidants and Antimicrobial Preservatives in Medicinal Products states that the physical and chemical compatibility of the preservative (or antioxidant) with the other constituents of the formulation, the container and closure must be demonstrated during the development process. The minimum concentration of preservative should be used, which gives the required level of efficacy, as tested using pharmacopoeial methods. Certain preservatives should be avoided under certain circumstances, and preservatives should be avoided entirely for some specialised routes. The guidelines also require that both the concentration and efficacy of the preservative are monitored over the shelf life of the product. In multidose injectable products, the efficacy of the preservative must be established under simulated in-use conditions. Table 9.2 shows some of the most commonly encountered preservatives in licensed products and their typical concentrations. 

Healthcare personnel handwashes on the market today are predominantly liquid detergent formulations with sufficient active antimicrobial ingredient levels to achieve targeted organism reductions in both in vitro and in vivo tests as specified in the 1978 TFM. The most commonly used active ingredients are PCMX (0.24-3.75%) and triclosan (up to 1%) [58], Formulations are typically optimized systems rather than plain soap to which an antimicrobial agent has been added. 

Although all methods were initially comparable, with bacterial reductions of greater than 99%, recolonization of a test site was significantly reduced after 60 minutes when prepared with an alcohol and iodophor drape, compared with the other methods. Jeng and Severin investigated the performance of a povidone-iodine gel alcohol (5% povidone-iodine and 62% ethanol in gel form) as a 30-second, one-time application preoperative skin preparation [20]. The povidone-iodine gel alcohol formulation delivered rapid and persistent antimicrobial activity against a broad spectrum of bacteria, both in vitro and in vivo, and was found to be an effective skin preparation formulation for use in a single-step 30-second application. 

Figure 3 Test data for two different antimicrobial body wash treatments, povidone iodine (7.5%, PVPI) or a novel alcohol-based formulation (TSPN), followed with a preoperative preparation of like composition painted onto the test subjects immediately following the time = 0 hours sampling. Note that with the PVPl-based treatment regimen, the minimum 3 logio reduction from baseline microbial counts at 0.17 hours (10 min) is not obtained, whereas with the TSPN system the required reduction is obtained at both the 0.17-hour sampling as well as the 6-hour (end of typical surgical procedure) sampling. The average baseline microbial count for the subjects in this study was 5.4 logio organisms per cm" (n = 13).

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