Preservatives in Liquid
`Pharmaceutical Preparations
`
`Chawki Boukarim,* Sarah Abou Jaoudé, Rita Bahnam, Roula Barada,
`Soula Kyriacos
`
`Department of Pharmaceutical Sciences, School of Pharmacy, Lebanese American University,
`Byblos, Lebanon.
`
`KEY WORDS: Preservatives, sodium
`benzoate, potassium sorbate, methyl-
`paraben, quality control.
`
`ABSTRACT
`Sodium benzoate, potassium sorbate,
`and methyl hydroxybenzoate are com-
`monly used as preservatives in liquid
`pharmaceutical preparations. The pur-
`pose of this study is to determine the
`amount of the aforementioned preserva-
`tives in pharmaceutical products, as
`some recent studies have reported seri-
`ous side effects associated with the
`ingestion of these substances. The con-
`tent of 37 liquid pharmaceutical prod-
`ucts were simultaneously determined by
`high performance liquid chromatogra-
`phy. Preparations were analyzed in trip-
`licate for their preservative content
`using a sensitive and reproducible
`HPLC method modified in our laborato-
`ry. Preservative levels were found to fall
`outside the typical allowed concentra-
`tion range for 70% of the samples, with
`some exhibiting significantly higher con-
`centrations. The reason behind such
`findings is unclear, and could be due to
`poor quality control or to intentionally
`extend the shelf-life of the products.
`These findings highlight issues related to
`quality control and to patient’s safety.
`Consequences on patient health need to
`be evaluated, especially since most liq-
`14
`
`uid pharmaceutical products are admin-
`istered to the pediatric population.
`
`INTRODUCTION
`Preservatives have been commonly used
`as additives in pharmaceutical products,
`cosmetics, and food. Liquid preparations
`are particularly susceptible to microbial
`growth because of the nature of their
`ingredients. Such preparations are pro-
`tected by the addition of preservatives
`that prevent the alteration and degrada-
`tion of the product formulation.1
`Preservatives are mainly effective in
`controlling mold, inhibiting yeast
`growth, and protecting against bacterial
`proliferation. Their antimicrobial and
`antifungal properties make them an
`integral part of the product formulation.
`Among the most commonly used
`preservatives in the conservation of liq-
`uid pharmaceutical preparations are
`sodium benzoate, potassium sorbate, and
`methyl hydroxybenzoate (methyl-
`paraben). Their typical allowed concen-
`trations range respectively from
`0.1-0.2%, 0.1-0.2%, and 0.1-0.25%
`(w/w).1 The purpose of this study is to
`determine the amount of the former
`preservatives in liquid pharmaceuticals
`for quality assurance purposes as well as
`for patient safety. Accrued interest is
`given to preservatives as recent studies
`have reported serious side effects associ-
`ated with these substances. Skin reac-
`
`Vol. 9, No. 1 & 2, 2009 • The Journal of Applied Research
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`Figure 1: Concentration (%w/w) of Sodium Benzoate in labeled samples.
`
`tions such as rash, urticaria,,and contact
`dermatitis have been reported after top-
`ical application of potassium sorbate,-
`methylparaben,- and sodium benzoate-
`containing products.1, 2, 3 Other side
`effects have been reported after inges-
`tion of medications containing these
`preservatives such as the allergic poten-
`tial and estrogenic potential of
`parabens,2, 4 or the genotoxic activity
`potential of sodium benzoate.3
`
`MATERIALS AND METHODS
`Thirty seven liquid pharmaceutical
`preparations were purchased from ran-
`domly selected pharmacies in Lebanon.
`Not all preparations were labeled with
`respect to their preservative content: 19,
`8, and 1 preparation(s) were labeled for
`their methylparaben, sodium benzoate,
`and potassium sorbate content respec-
`tively, while 14 preparations were unla-
`beled with respect to one or more
`preservatives. Commercial brands of the
`liquid preparations were coded using
`letters (A to AL).
`Acetonitrile (HPLC grade) and sodi-
`um acetate (analytical grade) were pur-
`chased from Sigma, Germany. Sodium
`benzoate, potassium sorbate, and
`methylparaben standards were pur-
`chased from Fluka, UK. Standards were
`
`used to prepare standard working solu-
`tions using distilled water, to obtain
`stock solutions of 1 g/L concentration.
`Stock solutions were used to prepare
`solutions of lower concentrations (50,
`100, 200, and 400 mg/L) to build the cali-
`bration curve. The correlation coeffi-
`cients were above 0.999 in all cases.
`Preparations were analyzed in tripli-
`cate for their preservative content using
`a sensitive and reproducible HPLC
`method 5-8 modified in our laboratory.
`The HPLC system consisted of LC-10
`pump (Shimadzu), a variable ultraviolet
`detector monitor set at 229 nm
`(Shimadzu, SPD-10), and a Chromatopac
`Shimadzu (C-R8A) integrator.
`Separation was done using a pre-packed
`stainless steel column (15 cm x 0.46 cm)
`filled with Shimpack C18 10 µm Silica
`(Waters, Germany), and the flow rate
`was set to 1.5 mL per minute for sodium
`benzoate and potassium sorbate and 2
`mL/min for methylparaben. The preci-
`sion of the assay method was determined
`by calculating the relative standard devi-
`ation (inter- and intra-days) of the peak
`areas obtained after repeated injections
`(n=3) of all standard solutions. The rela-
`tive standard deviations of the areas
`were found to be less than 3.5%, which
`confirms the precision of the method.
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`The Journal of Applied Research • Vol. 9, No. 1 & 2, 2009
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`Figure 2: Concentration (%w/w) of Sodium Benzoate in unlabeled samples.
`
`One gram of each of the samples was
`accurately weighed and transferred to a
`100 mL volumetric flask. Mobile phase
`was added to volume and mixed. The
`mobile phase was an aqueous solution
`of acetonitrile 0.02 M sodium acetate
`buffer (20:80, v/v), adjusted to a pH 4.3
`with acetic acid. The mobile phase was
`filtered through a 0.45 Ìm filter and
`degassed before use. Twenty microliters
`of the filtrate were injected into the
`HPLC.
`The retention times for sodium ben-
`zoate, potassium sorbate and methyl-
`paraben were 5.2, 6.7, and 7.6 minutes,
`respectively.
`
`RESULTS AND DISCUSSION
`In the eight samples labeled as contain-
`ing sodium benzoate as a preservative,
`concentrations of the latter ranged
`between 0.012 - 0.85 % (w/w). Two sam-
`ples (A and G) included sodium ben-
`zoate in amounts significantly exceeding
`the typical allowed concentrations (up
`to four-fold difference) whereas two
`other products had a sodium benzoate
`concentration slightly exceeding that
`range (Figure 1).
`After screening the 12 unlabeled sam-
`ples, six were found to contain sodium
`benzoate in concentrations ranging from
`
`0.05-0.48 % (w/w). Only Product K con-
`tained the preservative in concentrations
`above the typical allowed concentrations
`(Figure 2). Two products exhibited sodi-
`um benzoate concentrations below typi-
`cal allowed concentrations. Additionally,
`as much as 50% of the pharmaceutical
`products containing sodium benzoate are
`formulated at a pH>5, at which the pre-
`servative is ineffective.
`As for potassium sorbate, the only
`labeled product included a higher
`amount of preservative. Many unlabeled
`samples were found to contain potassi-
`um sorbate as a preservative. As shown
`in Figure 3, products E and O exceeded
`the typical allowed concentrations for its
`use.
`Nineteen samples were labeled as
`having methylparaben as a preservative.
`It was found in concentrations ranging
`from 0.03-0.55 % (w/w). Only one
`labeled product included methylparaben
`in concentration exceeding the maximal
`allowed amount and 14 out of the 19
`samples had concentrations below the
`allowed range (Figure 4). None of the
`unlabeled samples exhibited concentra-
`tions exceeding the typical allowed
`range (Figure 5). All, however, had their
`methylparaben concentration below the
`allowed range.
`
`16
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`Vol. 9, No. 1 & 2, 2009 • The Journal of Applied Research
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`CONCLUSION
`Preservatives levels were found to fall
`outside the typical allowed concentra-
`tion range for 70% of the samples, with
`some exhibiting significant higher con-
`centrations. The present study highlights
`the high amount of preservatives that
`may be found in some liquid pharma-
`ceutical preparations. The reason behind
`such finding is unclear and could be due
`to poor quality control or to intentional-
`ly extend the shelf life of the products.
`Consequences to patients’ health need
`to be evaluated, especially since most
`liquid pharmaceutical products are
`administered to the pediatric popula-
`tion.
`
`ACKNOWLEDGEMENTS
`This work was supported by a grant
`from the Research Council at the
`Lebanese American University.
`
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