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Belgium Corresponding author. Magnus A Atemnkeng: eb. This article has been cited by other articles in PMC. Abstract Background Artemisinin-derivative formulations are now widely used to treat falciparum malaria. In addition to the active compound, the presence of a suitable preservative in these medicines is essential. In this study, an evaluation of the preservative content and efficacy in some dry suspensions available on the Kenyan market was performed.
After reconstitution of the powders in water, the dissolution of the preservatives was followed for 7 days. Antimicrobial efficacy of the preservatives was assessed by conducting a preservative efficacy test PET following the European pharmacopoeia standards. Results Four different preservatives were identified namely methylparahydroxybenzoate MP , propylparahydroxybenzoate PP , benzoic acid and sorbic acid. The other products did not conform.
Conclusion These results show that paediatric antimalarial dry powder formulations on the market may contain ineffective or incorrect amounts of preservatives. This is a potential risk to the patient. Studies conducted on the dry powder suspensions should include the analysis of both the active ingredient and the preservative, including the efficacy of the latter. Background The artemisinin-derivatives, artemether, artesunate, arteether and dihydroartemisinin, are currently the most potent antimalarial medicines on the market.
They are widely available in the different pharmaceutical dosage forms including tablets, injections, suppositories and dry powders [ 1 ]. Since artemisinin and its derivatives are poorly water-soluble and are not very stable in solution, the preparations have to be formulated in the dry form for subsequent reconstitution into a wet suspension with water just before use.
Of 18 spices tested against L. The most inhibitory fraction of the rosemary was -pinene. Hefnawy et al. Allspice was next most effective inactivating the microorganism in four days. In foods, both rosemary and sage have significantly reduced activity. Sensitivity of B. Sweet basil Ocimum basilicum essential oil has limited antimicrobial activity with linalool and methyl chavicol the primary antimicrobial agents. Against 33 bacteria, yeasts and molds in an agar well assay, basil essential oil extract was active against certain fungi, including Mucor and Penicillium species, but had little activity against bacteria Lachowicz et al.
Wan et al. Again, the compounds demonstrated limited activity against most microorganisms except Mucor and Penicillium. In contrast, methyl chavicol 0. Vanillin 4-hydroxymethoxybenzaldehyde is a major constituent of vanilla beans, the fruit of an orchid Vanilla planifola, Vanilla pompona, or Vanilla tahitensis.
Vanillin is most active against molds and non-lactic grampositive bacteria Jay and Rivers, Cerrutti et al. Many other spices have been tested and shown to have limited or no activity.
They include anise, bay laurel , black pepper, cardamom, cayenne red pepper , celery seed, chili powder, coriander, cumin, curry powder, dill, fenugreek, ginger, juniper oil, mace, marjoram, nutmeg, orris root, paprika, sesame, spearmint, tarragon, and white pepper Marth, ; Davidson and Naidu, It was first isolated from Streptomyces natalensis, a microorganism found in soil from Natal, South Africa Anonymous, Natamycin is active against nearly all molds and yeasts, but has little or no effect on bacteria or viruses.
Most molds are inhibited by 0. Most yeasts are inhibited by 1. Natamycin inhibits the production of mycotoxins by molds. Lodi et al. Adding natamycin to the cottage cheese dressing was even more effective in extending shelf life.
In addition to cheese, research with natamycin has shown it to be effective to inhibit fungal growth on fruits, meats and baked goods Ayres and Denisen, ; Shirk and Clark, ; Ayres et al. Nisin has a narrow spectrum inhibiting only grampositive bacteria, including Alicyclobacillus, Bacillus cereus, Brochothrix thermosphacta, Clostridium botulinum, C.
Against bacterial spores, nisin is sporostatic rather than sporicidal Delves-Broughton et al. Nisin does not generally inhibit gram-negative bacteria, yeasts, or molds. The spectrum of activity of nisin can be expanded to include gram-negative bacteria when it is used in combination with chelating agents e. Nisin activity generally increases with decreasing pH and decreased initial numbers of microorganisms. The presence of food components such as lipids and protein influence nisin activity Scott and Taylor, Nisin was less active against L.
This was probably due to binding of nisin to fat globules Jung et al. The primary mechanism of nisin is believed to be the formation of pores in the cytoplasmic membrane that result in depletion of proton motive force and loss of cellular ions, amino acids, and ATP Crandall and Montville, The application of nisin as a food preservative has been studied extensively Hurst and Hoover, ; Montville et al.
Based upon its target microorganisms, nisin application falls into one of three categories: 1 prevent spoilage by sporeforming bacteria, 2 prevent spoilage by lactic acid bacteria and related microorganisms or 3 kill or inhibit grampositive pathogenic bacteria, e. Somers and Taylor , studied the use of nisin to prevent C. Nisin was an effective antibotulinal agent at The higher The use of natural antimicrobials 17 nisin levels allowed for the safe formulation of cheese spreads with higher moisture content and lower salt concentration.
Delves-Broughton reported that nisin levels of 6 to Dean and Zottola found that nisin decreased L. Budu-Amoako et al. Nisin has shown some potential for use in selected meat products.
For example, Scannel et al. Nisin also has been suggested as an adjunct to nitrite in cured meats for the purpose of preventing the growth of clostridia Caserio et al. Although nisin appears to be more effective than nitrites at preventing the growth of some pathogenic and spoilage microorganisms in cured meats, it is yet to be shown to prevent C.
Since nisin is effective against most lactic acid bacteria but is inactive against yeasts, there is potential use for nisin in alcoholic beverages to prevent growth of spoilage lactic acid bacteria Ogden et al. Nisin has been evaluated for use as a component of antimicrobial packaging Ming et al.
Two limitations for the application of nisin to foods are losses during processing and during storage Thomas et al. Many of these compounds could potentially be used as food antimicrobials but, at the present time, few are approved by regulatory agencies to be added to foods in their purified form.
One approach to using these compounds has been to grow bacteriocin-producing starter cultures in a medium such as whey, non-fat dry milk or dextrose.
The fermentation medium is then pasteurized and spray-dried which kills the starter culture but retains the active antimicrobial. AltaTM at 0. Degnan et al. Counts of Listeria monocytogenes decreased 0. In an in vitro system, a number of variables or factors concerning the antimicrobial can be evaluated.
It is very important to evaluate the activity of a potential antimicrobial against multiple strains of pathogen since strain variation may occur. Another important variable is the initial number of microorganisms in the system. Since most antimicrobials are bacteriostatic rather than bactericidal, the higher the initial number, the shorter the shelf life of the product. The agar diffusion method has probably been the most widely used method for determination of antimicrobial activity throughout history.
In the test, antimicrobial compound is added to an agar plate on a paper disk or in a well. The compound diffuses through the agar resulting in a concentration gradient which is inversely proportional to the distance from the disk or well. Degree of inhibition, which is indicated by a zone of no growth around the disk or well, is dependent upon the rate of diffusion of the compound and cell growth Barry, Therefore, the antimicrobial evaluated should not be highly hydrophobic, as the compound will not diffuse and little or no inhibition will be detected.
Results of this test are generally qualitative. Agar and broth dilution assays are generally used when quantitative data are desired. In both methods a single statistic, known as the minimum inhibitory concentration MIC , is generated.
In the dilution assays, a number of containers are prepared to contain a single concentration of antimicrobial in a microbiological medium. A test microorganism is exposed to the antimicrobial and incubated for a specified period, usually at least 24 hr.
The MIC is generally defined as the lowest concentration of an antimicrobial that prevents growth of a microorganism after the specified incubation period. These methods provide little information concerning the effect of an antimicrobial on the growth or death kinetics of a microorganism. Concentrations of an antimicrobial which are below the MIC may still cause an increased lag phase, reduced growth rate or even initial lethality followed by growth.
In food products, total inhibition of a pathogen or spoilage microorganism is not always required. An increased lag phase, especially under conditions of severe abuse, is often sufficient to protect the consumer. Therefore, to determine the effect of a compound on the growth or death The use of natural antimicrobials 19 kinetics of a microorganism, a method is required that produces an inhibition curve using a colony count procedure. This method is versatile but has some disadvantages including the fact that no single statistic is produced to compare treatments such as MIC and it is labor intensive and expensive.
A second method for determining antimicrobial effectiveness over time is to measure turbidity increases with a spectrophotometer. A major disadvantage to this type of analysis is sensitivity of the instrument.
Spectrophotometers generally require log 6. This may create a situation in which no growth i.
Many researchers have made claims concerning the potential effectiveness of natural antimicrobials based solely upon data from testing in microbiological media only to find that a compound is much less effective or ineffective in a food system. Application testing can be very complex and include a number of variables including microbial, food-related intrinsic , environmental extrinsic and process Gould, Because of the variation in characteristics and activities among naturally occurring compounds, it is somewhat difficult to generalize regarding methods for applying the compounds.
Even among regulatory-approved antimicrobial compounds, such as benzoic acid or sorbic acid, there are no standard methods for evaluating activity or application procedures. Applying the antimicrobial to a food involves either a model food system or the actual food. A great deal of information can be gained by using model systems that contain a percentage of a food in a buffer or microbiological medium.
These systems demonstrate potential interferences by food components but allow for easier sampling by the researcher. The microorganism or microorganisms utilized should be a natural contaminant bioburden or a pathogen of interest and incubation conditions should reflect use and abuse. Success of application testing may be determined by increased shelf life or reduction of potential health hazards. Much 20 Food preservation techniques of the early research, particularly on microbially derived antimicrobials focused on activity in microbiological media only.
As has been stated previously, many compounds are effective in microbiological media but have reduced or no activity in foods. Other excipients, or the active pharmaceutical ingredient API may enhance or weaken the efficacy of the preservative system by a variety of mechanisms.
It may also be possible, at product design stage to formulate the product such that desired pH is aligned with optimal preservative efficacy.
Many pediatric liquid formulations particularly those containing antibacterial agents are formulated so that pH is in the range of 4. Historically, the parabens were always utilized when the target pH of the formulation was between pH A recent article29 on the assessment of the antimicrobial efficacy of two preserved eye drop formulations highlighted some of these key issues.
The author29 described an anti-histamine eye drop product, where the preservative, i. BKC was present at 0. In contrast, in an anti-inflammatory eye drop formulation, the preservative, i. BKC was present at a much lower level 0.
These two formulations were challenged using the five standard pharmacopeial organisms see The Preservative Challenge Test Antimicrobial Effectiveness Test and Burkholderia cepacia, a well-established objectionable organism. The AET data demonstrated an acceptable kill rate for all organisms, except Pseudomas aeruginosa in the anti-histamine formulation. Interestingly, despite BKC being present in this formulation at 5x the level of the other formulation it was ineffective at killing this pharmacopoeial challenge organism.
As BKC is effective over a very broad pH range 33 it is very unlikely that differences in formulation pH, per se, will have impacted on its comparative efficacy.
The likely reasons for preservation failure are twofold, i synergistic combinations of preservatives are often required before they are effective; as certain bacteria can be resistant to single preservative systems, e. BKC,34 and ii other excipients can potentiate the activity of preservatives by reducing the water activity of the formulation e.
PVP35, polyols,35 etc. A decision can then be made to include those organisms in the preservative efficacy testing programs; with the caveat that the pharmacopeial methodology will not be optimized for this additional organism. Discussion It will be evident from the performance criteria outlined in Table 2, and the supplementary strictures on use of some agents that the current limited list of acceptable preservatives is likely to be further reduced in the future.
Physicochemical and organoleptic properties also limit choice, as do possibilities for interactions with the active ingredient or excipients particularly those with large surface areas or the pack or delivery system.
For example, propylparaben has significantly decreased aqueous solubility compared to methylparaben, which can cause problems during the manufacture of the oral liquid product. In addition, the USP38 and Ph. As indicated earlier, the list may be supplemented by additional resistant organisms that may be associated with a particular process, facility or material, e.
Burkholderia cepaceia an opportunistic pathogen often isolated in manufacturing environments, or Bacillis subtilis, a spore-forming bacteria. Zygosaccharomyces rouxii is also a useful test organism in formulations with high sugar or polyol content. Acceptance criteria for USP39 and JP41 are broadly similar with some differences between product type and presentation.
All require satisfactory reduction for each challenge organism with no subsequent increase from the initial count after and days. It is widely recognized that the criteria of the Ph.
The Ph. Scheler et al. All preparations, even those without sorbic acid, met the criteria for oral products with aqueous bases according to USP and JP, which define no increase from the initial count at 14 and 28 days. However, the Ph. AET tests form part of the preservative optimization studies. Some regulatory authorities may also require confirmation that the product is adequately preserved during its in-use period, when it is being routinely opened, dispensed and closed and the potential for microbial contamination is at its highest.
As part of process development activities, most companies will also challenge the preservative system at the extremes of pH, preservative concentration, etc.
Techniques include ATP bioluminescence, electrical impedance and chemiluminecence. Inevitably, much development, validation and corroboration would be required before adopting a replacement technique. Meanwhile, some issues could be addressed to ensure a more pragmatic approach is taken with the current requirements. Eur requirements42 with attendant cost and delays to product development , it would be beneficial for the Pharmacopeial Discussion Group PDG to consider AET harmonization initiatives.
Align Test Duration with Product Usage Some oral liquid products are manufactured as solids that are constituted with water prior to use. Shelf life in the solution state is typically constrained by drug instability, as such, 7 or 10 day in-use periods are common. Performance criteria for preservatives in such products should reflect the in use period. Running the test for 30 days, when the product may fail the test for other reasons e.
These initiatives fuel demands that preservatives be omitted from medicinal products, particularly pediatric formulations. At the same time, many materials that are used as excipients, are of biological provenance and cannot realistically be sold as sterile. Furthermore, their nature or physical properties ensure that they cannot readily be sterilized before or during incorporation into multiuse oral liquid products.
Terminal sterilization may not be feasible for the same reasons. The presence of low levels of microbes cannot be obviated in such cases and, if the vehicle allows or encourages microbial growth over the necessarily long shelf life that pharmaceutical products must possess the inclusion of a preservative in the product is simply a prudent way to assure an important quality attribute and safeguard the patient. In practical terms, removing preservatives from a medicinal product even if technically feasible would require a comprehensive re-think of quality systems throughout manufacture to provide a product that is essentially microbe-free i.
Product manufacture in a microbe-free environment, i. In some cases it may be possible to reduce or eliminate contamination by procedures during or at end of manufacture, as is possible with some food and confectionary products.
However, there is a general regulatory reluctance to use preservatives to address poor manufacturing practices, to reduce viable microbial population of a non-sterile product or to control the bio-burden prior to sterilization of a multi-dose sterile product. Product is packaged in units that maintain closure integrity during shelf life e. BFS ampoules. Single-use units e. Several preservation-free intranasal devices are available for commercialization,46 but there are relatively few multi-use preservativefree nasal commercial products.
Some companies are developing a multi-use nasal device with self-sealing nozzle that could maintain sterility after repeated microbial challenge tests.
Many pharmaceutical products already utilize such approaches. The in-use period where patients use the product still remains the Achilles heel, when the closure needs to be broached or penetrated so that a dose can be withdrawn and more importantly where there is potential for microbial contamination. There is no universally reliable way that this can be achieved for each and every product type.
Non-inclusion can result in serious patient health consequences. There are a limited number of regulatory-approved preservatives that can be included in these multi-use medicinal oral or topical products and the number is constrained even further in parenteral products.
In the nearly 6 years since our first review, additional preservatives, e. However, as industry typically develops multi-national products aimed at all of the major market, the strictest regulatory hurdles drive decision making. Thus it is very unlikely, that companies would develop multi-use products preserved with parabens for just the US market. Furthermore, it may be time to revisit the tests and performance requirements that products must undergo before being considered to be adequately preserved; although for exactly the reasons already outlined it is the Ph.
Preservative-free approaches are still in their infancy and much more research is required before they can be considered on an equal footing with preserved approaches. However, several preservativefree intranasal and ophthalmic devices are available and offer some promise.
Finally, there is increasing regulatory expectation particularly in the US that additional challenge organisms, particularly the opportunistic pathogen, B. References Moreton, C.