Russell, Hugo & Ayliffe’s
`Principles and
`Practice of
`Disinfection,
`Preservation &
`Sterilization
`
`Nalox1214
`Nalox-1 Pharmaceuticals, LLC
`Page 1 of 33
`
`

`

`Russell, Hugo & Ayliffe’s
`Principles and
`Practice of
`Disinfection,
`Preservation &
`Sterilization
`
`EDITED BY
`Adam P Fraise MB BS FRCPath
`
`Consultant Medical Microbiologist and Director
`Hospital Infection Research Laboratory
`City Hospital
`Birmingham, UK
`
`Peter A Lambert BSc PhD DSc
`
`Reader in Microbiology
`Pharmaceutical and Biological Sciences
`Aston University
`Birmingham, UK
`
`Jean-Yves Maillard BSc PhD
`
`Senior Lecturer in Pharmaceutical Microbiology
`School of Pharmacy and Biomolecular Sciences
`University of Brighton
`Brighton, UK
`
`FOURTH EDITION
`
`Nalox1214
`Nalox-1 Pharmaceuticals, LLC
`Page 2 of 33
`
`

`

`© 1982, 1992, 1999 by Blackwell Science Ltd
`© 2004 by Blackwell Publishing Ltd
`Blackwell Publishing, Inc., 350 Main Street, Malden, Massachusetts 02148-5020, USA
`Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK
`Blackwell Publishing Asia Pty Ltd, 550 Swanston Street, Carlton, Victoria 3053,
`Australia
`
`The right of the Author to be identified as the Author of this Work has been asserted in
`accordance with the Copyright, Designs and Patents Act 1988.
`
`All rights reserved. No part of this publication may be reproduced, stored in a retrieval
`system, or transmitted, in any form or by any means, electronic, mechanical,
`photocopying, recording or otherwise, except as permitted by the UK Copyright,
`Designs and Patents Act 1988, without the prior permission of the publisher.
`
`First published 1982
`Second edition 1992
`Reprinted 1994 (twice)
`Third edition 1999
`Fourth edition 2004
`
`Library of Congress Cataloging-in-Publication Data
`
`Russell, Hugo & Ayliffe’s Principles and practice of disinfection,
`preservation and sterilization / edited by Adam P. Fraise, Peter A.
`Lambert, Jean-Yves Maillard. —4th ed.
`p. ; cm.
`Rev. ed. of: Principles and practice of disinfection, preservation, and
`sterilization, 1999.
`Includes bibliographical references and index.
`ISBN 1-4051-0199-7
`1. Disinfection and disinfectants. 2. Sterilization. 3. Preservation
`of materials.
`[DNLM: 1. Disinfection —methods. 2. Sterilization —methods.
`3. Anti-Infective Agents. 4. Preservatives, Pharmaceutical. WA 240 R963
`2004] I. Title: Principles and practice of disinfection, preservation
`and sterilization. II. Russell, A. D. (Allan Denver), 1936–. III. Hugo,
`W. B. (William Barry). IV. Ayliffe, G. A. J. V. Fraise, Adam P.
`VI. Lambert, Peter A. VII. Maillard, J.-Y. VIII. Principles and practice of
`disinfection, preservation, and sterilization. IX. Title.
`RA761.P84 2004
`614.4¢8 —dc22
`
`2003017281
`
`ISBN 1-4051-0199-7
`
`A catalogue record for this title is available from the British Library
`
`Set in 9.5/12 Sabon by SNP Best-set Typesetter Ltd, Hong Kong
`Printed and bound in the United Kingdom by CPI Bath
`
`Commissioning Editor: Maria Khan
`Managing Editor: Rupal Malde
`Production Editor: Prepress Projects Ltd
`Production Controller: Kate Charman
`
`For further information on Blackwell Publishing, visit our website:
`http://www.blackwellpublishing.com
`
`Nalox1214
`Nalox-1 Pharmaceuticals, LLC
`Page 3 of 33
`
`

`

`Chapter 14
`Preservation of medicines and cosmetics
`
`Sarah J Hiom
`
`1 The nature of medicines and cosmetics
`2 The consequences of microbial contamination
`3 The effect of formulation parameters on microbial
`contamination and spoilage
`4 Attenuation of preservative efficacy
`5 Enhancement of preservative efficacy
`6 Prediction of preservative efficacy
`
`7 Adverse reactions of users to preservatives
`8 Regulatory aspects of the preservation of medicines and
`cosmetics
`9 The use of preservatives in medicines and cosmetics
`10 Alternatives to conventional preservatives
`11 References
`
`1 The nature of medicines and cosmetics
`
`Medicines are formulated to assist in the adminis-
`tration of drugs to treat or prevent diseases or to
`alleviate symptoms in patients. Medicines can be
`delivered by a wide variety of routes, from relative-
`ly non-invasive topical applications to highly inva-
`sive injections. Cosmetics, however, are designed to
`deliver agents that enhance personal appearance,
`modify body odour or assist in body cleansing.
`Application is largely restricted to the skin, although
`such products as toothpaste or those for ‘feminine
`hygiene’ may come into contact with mucous mem-
`branes. Eye-area cosmetics may also come into sec-
`ondary contact with the cornea and conjunctiva.
`Although the intended outcomes for medicines
`and cosmetics are fundamentally different, there
`are many similarities in the nature of the formula-
`tions created and the uses (and abuses) to which
`both can be subjected, including common microbi-
`ological problems. In order to create elegant prod-
`ucts that are also efficacious, stable and safe to use
`throughout their intended shelf life, it is often neces-
`sary to include several other ingredients in addition
`to the specific therapeutic agent or that producing
`the cosmetic effect. While a few formulations may
`be simple aqueous solutions or dry powders, many
`are extremely complex, both in the number of
`ingredients used and in their physicochemical
`complexity. Some indications of this variation and
`complexity of medicinal and cosmetic formulations
`
`484
`
`can be obtained from the reviews of Friberg (1984),
`Eccleston (1990), Frick (1992), Pena et al. (1993)
`and Lund (1994).
`The possibility that microorganisms might cont-
`aminate medicines and cosmetics during manufac-
`ture, storage or use must be addressed to ensure the
`continued stability and safety of the product. The
`complex chemical and physicochemical nature of
`many formulations is often found to be conducive
`to the survival and even multiplication of such con-
`taminants, unless specific precautions are taken to
`prevent it. Such survival, and even growth, may
`result in appreciable damage to the product and/or
`the user. The consequences of this damage will in-
`creasingly be reflected in loss of remuneration and
`prestige for the manufacturer as strict product-
`liability legislation continues to come into opera-
`tion. Good manufacturing practices should provide
`adequate control of contamination from raw mate-
`rials and processing activities (see Chapter 21;
`Clegg & Perry, 1996; Anon., 1997a; Beaney, 2001).
`One procedure adopted to limit the establishment
`of microbial contamination after manufacture is to
`include antimicrobial preservatives in the formula-
`tions, although other protective techniques can be
`used instead of, or in combination with, these
`agents. Selection of a preservative system is a com-
`plex issue. It is essential to understand and fully
`evaluate the preservative needs and problems of in-
`dividual products and to be aware of how potential
`antimicrobial agents may behave in that formula.
`
`Nalox1214
`Nalox-1 Pharmaceuticals, LLC
`Page 4 of 33
`
`

`

`The ideal properties required of a preservative
`have been described (Beveridge, 1998) together
`with monographs of available agents (Steinberg,
`1996; Kibbe, 2000; BP, 2001). Very few preser-
`vatives are able to meet all the required criteria
`and it is often a case of ‘best choice under current
`circumstances’. However, the selection process
`will include consideration to the properties of
`the formulation, preservative and likely challenge
`microbes, together with an evaluation of the intend-
`ed use of the product and the associated contamina-
`tion risks.
`
`2 The consequences of microbial
`contamination
`
`Micro-organisms possess diverse metabolic activi-
`ties and are likely to present a variety of hazards
`(eg. infection, toxicity and degradation of the for-
`mulation) both to the user and to the stability of
`the products, if allowed to persist. The British
`Pharmacopoeia (BP, 2001) sets limits for the pres-
`ence of microorganisms in medicines, which vary
`depending on the product and its intended use.
`However, microbial contamination over and above
`these pharmacopoeial levels is still reported in dis-
`tributed UK medicines (Baird, 1988, Bloomfield,
`1990), although stricter regulatory controls have
`improved the situation compared with that of the
`pre-1970 period (Beveridge, 1975). Other indica-
`tions that the risk of microbial contamination is still
`a problem include reports that 20% of the UK drug
`alerts since October 2001 were due to an inability
`to provide microbial assurance to the required
`level (Defective Medicines Report Centre) and that
`7.1% of Medicines Control Agency (MCA) inspec-
`tion deficiency reports (1998–99) were associated
`with the potential for microbial contamination
`(Taylor et al., 2000). In-use contamination hazards
`also continue to be a problem, particularly for mul-
`tidose eye-drops (Geyer et al., 1995; Brudieu et al.,
`1999; Tasli & Cosar, 2001) and multidose injec-
`tions (McHugh & Roper, 1995). In the USA, con-
`cern currently centres around the microbial hazards
`that accumulate during the use of cosmetics (Anon.,
`1992a; Tran & Hitchins, 1994). Few recent pub-
`lished data have been found for cosmetic contami-
`
`Preservation of medicines and cosmetics
`
`nation in the UK, although anecdotal evidence sug-
`gests a similar situation to that in the USA.
`The most commonly reported microbial hazards
`found in liquid medicines and cosmetics are
`pseudomonads and their related Gram-negative
`rods, with spores (bacterial and fungal) predomi-
`nating in dry tablets, capsules and cosmetic
`powders. Shared-use cosmetics accumulate human
`microflora, such as Staphylococcus epidermidis,
`Staphylococcus aureus and corynebacteria, as well
`as pathogenic fungi, yeasts and bacterial spores.
`Those which contain water or become wet during
`use reveal pseudomonads and related bacteria.
`The clinical and pharmaceutical significance of
`such contamination of medicines has been reviewed
`by Ringertz & Ringertz (1982), Martone et al.
`(1987) and Denyer (1988) and for cosmetics by
`Sharpell & Manowitz (1991). The implications for
`product spoilage of both have been discussed by
`Spooner (1996) and Beveridge (1998).
`The risk (likelihood of harm actually occurring)
`associated with delivery of contaminated products
`is less clearly determined. It will depend upon the
`type of microorganism present, the infective dose
`(dependant on the ability of the formulation to
`encourage microbial survival and the level of pre-
`servative protection built into it), the route of
`administration of the product and the hosts resis-
`tance to infection (including immune status or de-
`gree of tissue damage at site of application). Prior to
`the 1960s, incidents of infection attributed to cont-
`aminated products seemed to be regarded as unfor-
`tunate but isolated occurrences, these included
`severe eye infections from contaminated oph-
`thalmic solutions (Theodore & Feinstein, 1952)
`and tetanus infection of newborn children from
`contaminated talc dusting powders (Tremewan,
`1946). During the 1960s, a number of key investi-
`gations demonstrated the existence of a much wider
`problem. Ayliffe et al. (1966) reported on an exten-
`sive UK outbreak of severe eye infections, traced to
`traditional but wholly inadequate official guide-
`lines for the preservation and manufacture of oph-
`thalmic solutions. The ‘Evans Medical disaster’, in
`which contaminated infusion fluids caused serious
`injury and contributed to some deaths, precipitated
`public awareness and led to an official inquiry
`(Clothier, 1972). In Sweden, Kallings et al. (1966)
`
`485
`
`Nalox1214
`Nalox-1 Pharmaceuticals, LLC
`Page 5 of 33
`
`

`

`Chapter 14
`
`linked an outbreak of salmonellosis to contaminat-
`ed thyroid tablets, and eye and other infections to a
`range of contaminated pharmaceuticals. Bruch
`(1972) in the USA similarly reported links between
`microbial contaminants in medicines and cosmetics
`and infections. Wilson, in a series of papers leading
`to those published by Wilson & Ahearn (1977),
`and Baker (1959) clearly implicated contaminated
`eye-area cosmetics with severe eye infections. The
`more general role of opportunistic pathogens, such
`as the pseudomonads, and their implication in
`nosocomial infections was also becoming more
`recognized at this time. These reports stimulated
`an appreciable tightening of regulatory controls in
`many countries, and it is generally believed that the
`present situation is greatly improved. Comprehen-
`sive reviews of the earlier work have been made for
`medicines by Fassihi (1991) and for cosmetics by
`Sharpell & Manowitz (1991). Appreciable num-
`bers of reports are still, however, being published of
`causal links between contaminated products and
`patient damage, of which a limited recent selection
`is now given.
`Although evidence of acute pathogenic infections
`from medicines has always been rare, a syrup
`diluted with contaminated water in a West African
`hospital pharmacy was implicated in an outbreak
`of cholera (E.G. Beveridge, personal communica-
`tion, 1993).
`There are still difficulties in preventing the build-
`up of pathogenic contaminants in multidose
`eye-drop containers during use (Tasli & Cosar,
`2001).The limited range of preservatives which are
`not damaging to the eye is also creating problems
`in controlling microbial proliferation, for example
`in contact lens maintenance (Hay et al., 1996;
`Sweeney et al., 1999). Additionally, there are cur-
`rently small but serious outbreaks of protozoal in-
`fections by Acanthamoeba, for which effective and
`safe preservatives are difficult to find (Seal, 1994;
`Lim et al., 2000). Total parenteral-nutrition infu-
`sions, compounded aseptically from sterile compo-
`nents, are conducive to microbial growth but
`cannot contain preservatives, due to their large vol-
`ume (Anon., 2001a). Recent cases of fatal infec-
`tions from contaminated units indicate an urgent
`need for improved systems for dispensing and
`protecting them from contamination (Freund &
`
`486
`
`Rimon, 1990; Pharmaceutical Journal, 1995;
`Allwood et al., 1997; Langford, 2000; Bethune
`et al., 2001). Patients whose resistance has been
`weakened by trauma, chemotherapy, tissue damage
`or other disease often succumb to infection by op-
`portunist contaminants which are unlikely to cause
`harm to ‘normal’ patients (Millership et al. 1986).
`The infection of haemophiliacs with human im-
`munodeficiency virus from human-derived factor
`VIII (Brown et al., 1995) and hepatitis C from
`blood-derived products
`(Anon., 1994c) has
`stimulated action on possible virus contamina-
`tion of other products derived from human or
`biotechnology-derived origin, as has the con-
`traction of Creutzfeldt–Jakob disease by patients
`treated with human growth hormone products
`from human origin (New Scientist, 1996a). Despite
`many well-publicized incidents, infection of pati-
`ents with burnt or otherwise damaged skin caused
`by using antiseptic cleaning solutions contaminated
`with Pseudomonas spp. continues (Norman et al.,
`1986; Arjunwadkar et al., 2001), as does infection
`from contaminated nebulizer solutions (Hamil
`et al., 1995; Dautzenberg, 2001).The liberation of
`endotoxins by growth of Gram-negative contamin-
`ants in large-volume intravenous infusions and
`peritoneal dialysis fluids remains a problem (Jarvis
`& Highsmith, 1984; Mangram, 1998). More re-
`cent are incidents of algal toxins, such as myco-
`cystins, surviving in process water and causing
`damage and even death when used for the dilution
`of kidney dialysates (New Scientist, 1996b). The
`implications of aflatoxin contamination in cosmet-
`ics has become of interest (El-Dessouki, 1992), with
`the suggestion that these toxins could penetrate the
`epidermis (Riley et al., 1985).
`With the link between infection and contamin-
`ated cosmetics long established (Bruch, 1972;
`Wilson & Ahearn, 1997), current concerns centre
`on the practice of in-store cosmetic multi-user
`testers. These have been shown to accumulate ap-
`preciable levels of contamination, including a vari-
`ety of hazardous bacteria, yeasts and fungi, which
`are able to initiate severe eye infections (Anon.,
`1992a; Tran & Hitchins, 1994) and infections asso-
`ciated with the use of contaminated hand creams
`and lotions (Anon., 1992a).
`Despite major advances in the quality of large-
`
`Nalox1214
`Nalox-1 Pharmaceuticals, LLC
`Page 6 of 33
`
`

`

`volume parenteral infusions, high numbers of
`localized and systemic infections occur which are
`directly attributable to the administration devices
`themselves, such as catheters and cannulae (Tebbs
`et al., 1996).
`Papers describing specific incidences of the mi-
`crobial deterioration of medicines and cosmetics
`used to be published regularly. However, these have
`been less frequently disclosed recently, possibly in
`keeping with the general concerns of both indus-
`tries about increasingly stringent product-liability
`legislation. There is good anecdotal and unattribut-
`able information to indicate that spoilage problems
`have not yet disappeared. Recent reviews of the
`spoilage aspects of microbial contamination of
`medicines and cosmetics have been made by Parker
`(1984), Spooner (1996) and Beveridge (1998).
`The weight of published evidence, both past and
`present, on the implications of microbial contami-
`nation for medicines and cosmetics demands that a
`careful and specific microbiological risk assessment
`is made for each individual product at its design
`and validation stages, using conventional risk-
`assessment techniques (Smith, 1984; McIntosh,
`1987; Begg, 1990; Rodford, 1996). These must
`take into account worst-case scenarios, such as the
`possibility that eye cosmetics may be applied whilst
`driving, where an applicator might scratch the
`cornea (Anon., 1991a), or that multidose eye-drop
`units may well receive varied and appreciable cont-
`amination during use by the lay public. Such assess-
`ments should take into account the highly critical
`expectations of the public concerning standards for
`medicines and other consumer products, which are
`usually far greater than those for their food.
`
`3 The effect of formulation parameters
`on microbial contamination and spoilage
`
`The inclusion of antimicrobial preservatives may
`not always be desirable or possible, or indeed able
`to offer adequate protection. In these circumstances
`it may be necessary to enhance their action, or re-
`place them, by subtle modification of various in-
`trinsic parameters in order to limit the risks of cont-
`amination and spoilage to acceptable levels. Such
`manipulations form the basis for the preservation
`
`Preservation of medicines and cosmetics
`
`and protection of many foodstuffs, where the
`ability to add antimicrobial preservatives is strictly
`limited by law. A wealth of basic and applied food-
`protection research is available for those who wish
`to assess these principles for application to medi-
`cines and cosmetics, and the reviews of Chirife &
`Favetto (1992), Dillon & Board (1994a), Gould
`(1996) and Roberts (1995) are recommended.
`Their application to pharmaceuticals and cosmetics
`has been considered briefly by Orth (1993b) and
`Beveridge (1998).
`The ultimate in-use contamination control
`would be to provide products as individually pack-
`aged, sterile, single-dosage applications. However,
`this is only cost-effective where there is a high infec-
`tive risk such as with eye-drops for hospital use or
`where preservatives cannot be used due to overrid-
`ing toxicity concerns. Possibly the worst-case sce-
`nario of in-use contamination is that of cosmetic
`tester kits provided in stores for repeated use by var-
`ious customers, resulting in appreciable and varied
`levels of contamination (Tran & Hitchins, 1994).
`The repeated use and dilution of mascara, eye-liner
`and eye-shadow with variously moistened applica-
`tors also results in a build-up of contamination and
`attenuation of preservative protection (Orth et al.,
`1992). Other attempts to reduce in-use contamina-
`tion include the replacement of wide-mouthed jars
`(having ready access for fingers) by flexible tubes
`for creams and ointments, the redesign of bottles to
`reduce the accumulation of liquid residues around
`the mouth and neck and the introduction of plastic
`‘squeezy’ eye-drop bottles instead of the conven-
`tional glass-dropper bottle (Allwood, 1990a).
`Brannan & Dille (1990) also found that slit-top and
`pump-action closures provided greater protection
`for a shampoo and skin lotion than a conventional
`screw-cap closure. Wet in-use bars of soap are also
`a known source of microbes (Brook & Brook,
`1993) and there is now a move towards liquid
`soap dispensers in an attempt to reduce hand
`contamination.
`The longer a product is in use, the greater the op-
`portunity for contamination to accumulate and the
`chance of growth and spoilage to ensue. Medicines
`prepared extemporaneously under section 10 ex-
`emption of the Medicines Act (1968) are dispensed
`with short shelf lives in an attempt to reduce the risk
`
`487
`
`Nalox1214
`Nalox-1 Pharmaceuticals, LLC
`Page 7 of 33
`
`

`

`Chapter 14
`
`of growth and contamination. Oldham and
`Andrews (1996) found that contamination could
`be held at reasonable levels in many types of unpre-
`served eye-drops for up to 7 days, provided they
`were also stored in a refrigerator.
`The response of contaminants to the physico-
`chemically complex environment of many phar-
`maceutical and cosmetic formulations will differ
`significantly from that in simple laboratory media
`(Beveridge, 1998), being markedly influenced by
`their spatial arrangement (Wimpenny, 1981) and
`the phase status of the systems (Verrips, 1989).
`There are many reports of modified behaviour of
`microorganisms at solid–liquid and liquid–liquid
`interfaces, but the evidence for increased resistance
`or longevity compared with freely planktonic
`situations is far from clear (van Loosdrecht et al.,
`1990). An increasing understanding of the survival
`strategies of microorganisms in sparse ecosystems
`(Roszac & Colwell, 1987) may provide an insight
`into the longevity of vegetative contaminants in
`seemingly unlikely products, e.g. Salmonella spp.
`in chocolate (Greenwood & Hooper, 1983) and
`thyroid tablets (Kallings et al., 1966) or vegetative
`bacteria in ‘dry’ powdered ingredients such as
`plant material, starch, hydroxymethylcellulose and
`gels such as aluminium hydroxide (Payne, 1990,
`Kneifel, 2002).
`The nutritional requirements of most sapro-
`phytic non-fastidious spoilage contaminants are
`likely to be well met in almost all pharmaceuticals
`and cosmetics, since many ingredients are easily
`biodegradable, and even the trace residues of non-
`specific chemical contaminants present in most
`commercial ingredients are likely to provide ample
`nutrients to permit growth. For example, even stan-
`dard distilled and demineralized water contains
`sufficient trace nutrients to permit ample growth of
`pseudomonads and related species (Favero et al.,
`1971). It is usually the physicochemical parameters
`of the formulation which are the determining fac-
`tors as to whether growth will or will not take place.
`The complex water requirements of micro-
`organisms (Gould, 1989; Wiggins, 1990) necessitate
`that, if they are to replicate, they must successfully
`compete for ready access to water against the other
`ingredients of a formulation that can also interact
`with it, often in strong and complex manners
`
`488
`
`(Beveridge & Bendall, 1988). Manipulation of
`product water activity (Aw, an indicator of the
`ready availability of water to contaminants) to a
`level below the minimum essential for growth offers
`a major potential for protection of some products.
`It is possible to reduce the Aw of tablets, pastilles,
`capsules and powders sufficiently by drying to
`provide their major mode of spoilage protection,
`although some contaminants may continue to sur-
`vive in a senescent state for a considerable time
`(Sommerville, 1981; Flatau et al., 1996). Friedel
`(1999) has proposed reducing the number of micro-
`biological attribute tests carried out on pharmaceu-
`ticals, based on information collated on the Aw
`content of different types of products and the ideal
`Aw growth requirements of the likely contaminat-
`ing microorganisms (Cundell, 1998). These figures
`may also be used to assist decisions concerning the
`need to include preservatives in a product. For ex-
`ample rectal ointments have an Aw of approximate-
`ly 0.26 and as no organisms are expected to
`proliferate below an Aw of 0.5, preservatives are not
`recommended in these type of preparations. The
`proposed reduction in Aw must be maintained
`throughout the life of the product, possibly by using
`water-vapour-resistant bottles or film-strip pack-
`ing, otherwise protection will be lost. The use of
`vapour-repellent film coatings (Whiteman, 1995)
`has been suggested to assist in the control of
`spoilage of bulk tablets intended for distribution to
`humid climates (Fassihi et al., 1978). The Aw of
`some aqueous systems can be lowered sufficiently
`to give useful protection by the addition of quite
`large amounts of water-binding low-molecular-
`weight solutes: sucrose (66% w/v, approx.
`Aw = 0.86) in, for example, reconstituted antibiotic
`syrups; sorbitol (> c. 35% w/v) for dentifrice pastes
`(Morris & Leech, 1996); glycerol (> c. 40%) for
`cosmetic lotions, and urea (10–20%) for some cos-
`metics (Jackson, 1993). Limtner (1997) described
`the use of polyacrylamide hydrogels in cosmetic
`creams to enhance formulation robustness, pre-
`sumably by very effectively lowering Aw. While
`even the most osmotolerant bacteria (micrococci)
`will require Aw levels in excess of c. 0.82 for growth,
`and few common fungi or yeast will grow below an
`Aw of 0.65 (Beuchat, 1983), one needs to be on
`guard against the rare, rogue, highly osmotolerant
`
`Nalox1214
`Nalox-1 Pharmaceuticals, LLC
`Page 8 of 33
`
`

`

`mould or yeast, for which antimicrobial preserva-
`tion may also be necessary. Strongly alcoholic
`formulations, such as perfumes, have a low Aw, as
`well as being antimicrobial in their own right.
`Condensed-moisture films can develop with suffi-
`ciently high Aw on the surfaces of waxy cosmetics,
`such as lipsticks, or highly viscous formulations,
`such as toothpastes, or on compressed cosmetic
`powders, to permit localized fungal growth, when
`they are persistently exposed to humid environ-
`ments, such as steamy bathrooms, or if moisture is
`regularly applied by mouth or applicator during
`use. Growth of contaminants has occurred in con-
`densed films under the tops of containers formed
`when hot aqueous products have been packed into
`cold containers. This effect can also result in appre-
`ciable dilution and loss of localized efficiency of
`any preservative present (Bhadauria & Ahearn,
`1980). Should sparse fungal growth be initiated
`on marginally dried products or those which have
`become damp during storage, such as tablets
`packed in bulk, water generated by respiration
`will create locally raised Aw levels and initiate a
`cycle of enhanced rates of growth, leading to appre-
`ciable levels of spoilage (Beveridge & Bendall,
`1988).
`The food industry’s wide use of pH reduction or
`gas environment modification of redox potentials
`to control spoilage is of limited application to med-
`icines and cosmetics. However, the pH of a product
`will influence the type of spoilage that might be
`initiated, although this itself may result in a pH
`change, allowing other contaminants to take over.
`Thus, the low pH of fruit-juice flavoured medicines
`may aid fungal spoilage but suppress bacterial
`growth, while the slightly alkaline antacid mixtures
`would favour growth of pseudomonads and related
`bacteria. It is unlikely that the redox potential
`of most pharmaceuticals or cosmetics will be low
`enough to favour anaerobic spoilage, as seen in
`some foodstuffs. However, Smart & Spooner
`(1972) reported that initial spoilage and depletion
`of oxygen tension in a pharmaceutical product by
`a pseudomonad then permitted establishment of
`a secondary anaerobic attack, with striking
`consequences.
`Low temperature storage (8–12 °C) is used to im-
`prove the short-term stability of some unpreserved,
`
`Preservation of medicines and cosmetics
`
`or weakly preserved, medicines, such as unpre-
`served eye-drops (Oldham & Andrews, 1996) and
`reconstituted antibiotic syrups. Short-term deep
`freezing (–20 °C) is used to further limit the risk of
`growth of any contaminants introduced during
`the aseptic dispensing of total parenteral nutrition
`(TPN) products, prior to use. Where dispensed
`products are to be ‘stored in a cool place’ during
`use, the growth-inhibitory effect of the reduced
`temperature needs to be balanced against the conse-
`quent, and often significant, reduction in efficacy of
`any preservative present.
`Preservative action in most complex formula-
`tions usually results in residual, quite low, levels of
`saprophytic contaminants, which are not consid-
`ered to be of significant risk. Apparent rebound
`growth and spoilage of products after a prolonged
`period of time has been noticed and explained as a
`slow adaption to a new environment (Orth & Lutes
`Anderson, 1985) and was dubbed the Phoenix
`phenomenon by Orth (1993c). However, some
`researchers would refute this explanation and
`describe clumps of microorganisms being pro-
`tected from the preservative and being ‘released’ by
`laboratory recovery techniques (Friedel, 2001).
`Additionally, there are an increasing number of re-
`ports of inherent and seemingly acquired resistance
`of contaminants to a wide variety of preservatives.
`These phenomena and indications of their implica-
`tions for the formulator have been discussed in de-
`tail by Russell & Gould (1988) and Gilbert & Das
`(1996). Chapman et al. (1996) reviewed the phe-
`nomenon as it relates to preservative resistance
`emergence in cosmetic formulations.
`
`4 Attenuation of preservative efficacy
`
`Replacement in the early 1950s of anionic emulsi-
`fiers and relatively simple, slightly alkaline, creams
`by non-ionic, readily biodegradable, surfactants
`and more sophisticated formulations of more neu-
`tral pH resulted in an increasing number of spoil-
`age problems and a growing realization that
`preservative molecules were doing appreciably
`more in these complex systems than merely reacting
`with microorganisms. Concurrent interest in the
`physicochemical characteristics of multiphase
`
`489
`
`Nalox1214
`Nalox-1 Pharmaceuticals, LLC
`Page 9 of 33
`
`

`

`Chapter 14
`
`formulations revealed a variety of interactive possi-
`bilities for preservatives (Wedderburn, 1964).
`Reviews by van Doorne (1990), Kostenbauder
`(1991) and Dempsey (1996) provide detailed and
`current accounts of these phenomena and the Cos-
`metic, Toiletry and Perfumery Association (CTPA)
`Guidelines place them in a practical context
`(Anon., 1993b).
`It is important to obtain information on the in-
`trinsic properties of any preservative under con-
`sideration, from sources such as this book,
`Wallhaeusser (1984), the CTPA Guidelines (Anon.,
`1993b) and Martindale (2002), in addition to that
`provided by manufacturers. Detailed monographs
`for those preservatives commonly used in medi-
`cines have been prepared by Kibbe (2000). The
`aqueous solubility of some commonly used preserv-
`atives is low and some form salts or complexes with
`very low-solubility products, which precipitate
`from solution. Thus, the usefulness of chlorhexi-
`dine is restricted by its ability to form insoluble
`products with chloride, sulphate, phosphate or cit-
`rate ions and anionic surfactants. Quaternary am-
`monium preservatives form insoluble complexes
`with anionic surfactants and a range of anionic in-
`organic ions. Benzoates and parabens form insolu-
`ble and discolouring complexes with iron salts,
`chlorocresol precipitates with phosphates, and
`phenylmercuric nitrate precipitates with chloride
`ions. Bronopol has formed complexes with unpro-
`tected aluminium in flexible tubes. Contrastingly,
`preservatives with a high vapour pressure, such as
`chloroform, become appreciably depleted when
`containers are repeatedly opened during routine
`use (Lynch et al., 1977).
`Preservative stability will be influenced by for-
`mulation pH, storage temperature, shelf-life and
`conditions of processing. Thus, isothiazolinones
`(Anon., n.d.) and bronopol (McCarthy, 1984) dete-
`riorate significantly if processing temperatures
`exceed 55 °C. Chlorobutanol is unstable around
`neutral or alkaline pH and suffers appreciable de-
`struction at autoclaving temperatures (Holdsworth
`et al., 1984). Unless light-proof containers are used,
`the photocatalysed deterioration of preservatives
`such as the phenolics and quaternary ammonium
`and organomercurial agents may become signifi-
`cant. Loss of parabens will occur by steam distilla-
`
`490
`
`tion at process temperatures approaching 100 °C
`and they have poor stability in slightly alkaline, and
`above, products (Reiger, 1994). Transesterification
`between parabens and polyols, such as sorbitol,
`may occur and result in significant loss of activity
`(Runesson & Gustavii, 1986). Alternatively, the
`formaldehyde-releasing agents depend on suitable
`condi