Allergy to ophthalmic preservatives
`Jison Hong and Leonard Bielory
`
`UMDNJ 7 New Jersey Medical School, Newark, New
`Jersey, USA
`
`Correspondence to Leonard Bielow, MD, STARX
`Clinical Research Center, 400 Mountain Avenue,
`Springfield, NJ 07081, USA
`Tel: +1 973 912 9817; email: drlbielory@gmail.com
`
`Current Opinion in Allergy and Clinical
`Immunology 2009, 9:4477453
`
`Purpose of review
`The purpose of the present review is to examine the hypersensitivity reactions to
`preservatives in topical ophthalmic therapies.
`Recent findings
`Ocular hypersensitivity reactions to different types of preservatives in different chemical
`classes of topical ophthalmic treatments reviewed in the literature include lgE-mast cell
`mediated, cell mediated and toxic. Quaternary ammoniums (benzalkonium chloride) are
`most commonly (8% reported cases in OVID and PubMED based searches) associated
`with irritant toxic reactions whereas the organomercurials (thimerosal) and the alcohols
`(chlorobutanol) have the highest association (19% of OVID and 14% of PubMED
`based searches and 20% of OVID and 1 1% of PubMED searches), respectively, with
`allergic responses although the term allergy for the ‘alcohols’ appears to be actually an
`irritant effect whereas the organomercurials appear to truly interact with the immune
`system as neoantigens.
`Summary
`A large number of clinical and experimental studies reveal that preservatives in topical
`ophthalmic medications have been demonstrated to produce effects from inflammation/
`hypersensitivity to permanent cytotoxic effects involving all structures of the eye.
`
`Keywords
`eyedrops, hypersensitivity, ophthalmic, preservatives, topical, toxic
`
`Curr Opin Allergy Clin Immunol 9:4477453
`© 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
`152874050
`
`
`Introduction
`
`The use ofpreservatives in topical ophthalmic treatments
`is ubiquitous as they allow their use in compromised eyes
`with a poor defense against infection. However, although
`providing effective biocidal properties with well tolerated
`short-term use at low concentrations, preservatives can
`cause serious inflammatory effects on the eye with long-
`term use in chronic conditions, such as glaucoma or
`potentially ocular allergies. This study reviews the reac-
`tions associated with the most commonly used ophthal-
`mic preservatives in animal and human participants.
`
`
`
`Preservatives and hypersensitivity reactions
`in the eye
`There are many adverse reactions associated with topical
`ophthalmic medications. Most of these reactions are
`toxic and result from chemical
`irritation. Only about
`10% of all adverse reactions to topical ophthalmic drugs
`are truly allergic. Furthermore, allergies (IgE and cell
`mediated) are more commonly caused by the active
`pharmaceutical agents, such as neomycin or sulfa-based
`agents and rarely by preservatives or other additives [1,2].
`As the incorporation of preservatives in topical ophthal-
`mic solutions becomes more common,
`sensitization
`toward preservatives is increasing. The salts of benzalk-
`
`1528-4050 © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
`
`onium have been classified as being moderately aller-
`genic (4—11% skin test positive) whereas mercurial pro-
`ducts are strongly allergenic (1373770 of skin tests are
`positive). True allergic sensitization by other preserva-
`tives (chlorhexidine and chlorobutanol) is unusual.
`
`The different types of hypersensitivity reactions can be
`separated into the following categories: allergic reactions
`(lgE-mast cell mediated hypersensitivity), cicatrizing
`allergic conjunctivitis (type II and III hypersensitivities)
`due to antibody localizing to ocular tissue or immune
`complexes deposition and allergic contact conjunctivitis,
`a type IV hypersensitivity reaction (Table 1)
`[3—5].
`The term allergy in the ophthalmological literature is
`commonly used interchangeably with immunological
`responses of any type and does not necessarily denote
`an lgE-mast cell mediated process.
`
`
`Preservatives
`
`Nature and properties of the various preservatives: the
`different chemical classes (Table 2).
`
`
`Benzalkonium chloride
`a
`is
`Benzalkonium chloride,
`also known as BAC,
`quaternary ammonium, which is a highly hydrosoluble
`DO|:10.1097/AC|.ObO13e3283306990
`
`
`Copyright © :ippincott \Mlliams & Vlfilkins. Unauthorized reproduction of this article is prohibited.
`
`Argentum Pharm. LLC v. Alcon Research, Ltd.
`Case IPR2017-01053
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`

`448 Eye allergy
`
`Table 1 Hypersensitivity reactions in the eye and the associated preservatives
`
`Type of reaction Description
`
`Ocular manifestations
`
`Preservative association
`
`Type I
`hypersensitivity
`
`Triggered by the classical
`activation of the IgE-Mast
`Cell axis and its associated
`early phase and late phase
`responses with an inflammatory
`reaction characterized by infiltration
`of PMNs, eosinophils and
`mononuclear cells into the
`corneo-conjunctival tissues and
`are also known as anaphylactoid
`reactions.
`
`Type II–III
`hypersensitivity
`
`Antibody-mediated
`hypersensitivity
`reactions are also known
`as localized antibody-specific
`disease or immune
`complex mediated reactions.
`
`Type IV
`hypersensitivity
`
`Drug induced ocular allergies
`are most often the result of
`type IV hypersensitivity.
`Type IV hypersensitivity is
`cell mediated and also
`known as delayed-
`hypersensitivity reactions.
`(contact conjunctivitis)
`
`Characterized by acute itching, conjunctival
`hyperemia and chemosis and by edema of
`the eyelids either as urticaria (hives or wheals)
`in the superficial layers of the skin (epidermis
`and dermis) or angioedema (in the deeper
`subcutaneous tissues) or both, as well as
`production of significant quantities of mucus,
`edema and neovascularization of the cornea,
`and inflammation of the iris and infiltration of
`the anterior chamber [1]. Histopathologically,
`these reactions show edema of the eyelids
`and conjunctiva, dilation of the venules and
`capillaries and infiltration of lymphocytes,
`eosinophils and neutrophils.
`Cicatrizing allergic conjunctivitis
`(pseudopemphigoid) reaction is a response
`to topical medication that results in
`cicatrizing conjunctivitis resembling
`ocular cicatricial pemphigoid (OCP). It is
`characterized by scarring in the bulbar,
`forniceal, and palpebral conjunctiva that
`is worse inferiorly along with conjunctival
`keratinization and punctual occlusion.
`The progression of symptoms cease
`once the offending medication is
`discontinued [1].
`Many of the type IV hypersensitivity reactions
`occur at the eyelid level that often makes it
`difficult to differentiate from other causes of
`eyelid inflammation or contact dermatitis.
`These types of allergic reactions can be
`detected by skin tests.
`
`Allergic contact lens
`keratoconjunctivitis (CLK)
`reaction is a type IV delayed
`hypersensitivity reaction
`secondary to use of
`contact lens solution.
`
`The patient must be exposed to the preservative
`for several years before sensitization occurs.
`It is characterized by progressively increasing
`intolerance of contact lenses, punctuate
`staining along the limbus for 360 degrees
`and above the superior limbus, and a
`whorl-like staining over much of the cornea.
`There is also an associated fine papillary
`conjunctival reaction [1].
`
`Chlorhexidine: a 58-year-old male
`patient developed anaphylactic
`shock, possibly due to the use of
`chlorhexidine as an ophthalmic
`wash solution. He was successfully
`resuscitated without any sequelae.
`The patient had increased levels of
`both histamine and tryptase. The
`skin test for allergy resulted in
`strong positive to chlorhexidine.
`There have been many reports
`regarding severe adverse reactions
`associated with use of
`chlorhexidine [3].
`BAC, Kilp [4] report a case of
`a woman instilling artificial tear
`solution containing benzalkonium
`for treatment of dry eye syndrome,
`who developed a superficial
`keratitis which regressed after
`substitution with a preservative-free
`treatment [5].
`
`Thimerosal: the manifestations of the
`ocular delayed hypersensitivity
`reactions include conjunctival
`hyperemia, corneal infiltrates, and
`intolerance to lens wear with the
`use of soft contact lens solutions
`or other topical ophthalmic
`medications containing thimerosal.
`Delayed hypersensitivity to
`thimerosal can be demonstrated
`by an occlusive patch test or
`intradermal injection [5].
`The classic cause of CLK is
`thimerosal, although it can also
`be attributable to chlorhexidine
`gluconate or EDTA.
`
`PMNs, polymorphonuclear leukocytes.
`
`bipolar compound with surfactant properties. Their
`mechanism of action primarily involves its intrinsic deter-
`gent activities depending on its concentration (ranges
`from between 0.004 and 0.02% in most topical products)
`leading to dissolution of bacterial cell walls and mem-
`branes. The spectrum of activity is mainly focused on
`Gram-positive bacteria. BAC is used in a wide range
`of commonly used products, such as soaps, cosmetics,
`cleaning products, ophthalmic preparations, disinfec-
`tants, and spermicides. BAC is known to cause
`damage/toxicity in almost all ocular structures.
`
`Animal studies
`Although the use of BAC does not appear to interfere
`with the absorption of the therapeutic agent in animal
`models [6], Becquet et al. [7] performed a study using
`
`rats to demonstrate the toxic and immunoallergic reac-
`tions that take place in the corneo-conjunctival surface
`after subjecting the eyes to the application of various
`preservatives. They found that even at low concen-
`trations of a single instillation of BAC, toxic effects on
`the corneo-conjunctival surface were noted most likely
`due to its intrinsic detergent properties that can alter
`tear fluid stability, particularly in its lipid phase. In
`rats treated with various other preservative solutions
`(BAC 0.01%, methyl parahydroxybenzoate 0.05%, and
`thiomersal 0.004%) there was an infiltration of immuno-
`competent cells into the limbus and bulbar conjunctiva
`that expressed class II and CD11b membrane HLA
`antigens
`(leukocyte integrin). Similar
`results were
`reported later by Baudouin [8] in rats treated by timolol
`0.5% containing BAC (0.01%) with abnormal expression
`
`Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
`
`

`

`Allergy to ophthalmic preservatives Hong and Bielory 449
`
`searchcategorywiththenumberoftotalsearchresultsforthatpreservative.(e.g.,searchingchlorobutanolandirritantyields3results,3isthendividedby46,thetotalnumberofresultsforthetermchlorobutanol,3/46is7%).
`bThenumberofresultswhencombiningthepreservativewiththesearchterms‘irritant’,‘inflammatory’,or‘allergic’isshowninthetable.Thenumberofparenthesisisthepercentagefoundbydividingthenumberofresultsinthisnew
`resultfromcombiningthespecificpreservativewiththeterms‘ophthalmology’and‘preservative’.(e.g.chlorhexidineandpreservativeandophthalmology).
`aThenumberofresultsfromanOVIDorPubMEDsearchforthespecifictypeofpreservative(e.g.,BAC,chlorhexidine,chlorobutanol,etc.)isshowninthetable.Thenumberinparenthesisrepresentsthenumberofsearchitemsthat
`Allsearchtermsintheyearrange2004tocurrent.
`
`OH
`
`O
`
`allergic23(7%)
`inflammatory5(1%);
`Irritant3(0.9%);
`
`339(0)
`
`allergic40(10%)
`inflammatory17(4%);
`Irritant9(2%);
`
`381(0)
`
`fungiratherthanbacteria
`
`Activitytargetsmoldand
`
`O
`
`benzoicacid
`parahydroxy-
`
`Estersof
`
`Parabens
`
`‘allergic’%
`‘inflammatory’,
`‘Irritant’,
`
`‘ophthalmology’)
`‘preservatives’and
`PubMEDsearch(and
`
`‘allergic’b%
`‘inflammatory’,
`‘Irritant’,
`
`‘ophthalmology’)a
`‘preservatives’and
`OVIDsearch(and
`
`Propertiesofclass
`
`Table2Preservativescommonlyusedintopicalophthalmicagents
`
`allergic4(0.6%)
`inflammatory59(9%);
`irritant2(0.3%);
`allergic3(11%);
`inflammatory2(7%);
`Irritant0;
`
`640(0)
`phenylethanol
`27(3);
`
`Chlorobutanol
`
`allergic1(0.5%)
`inflammatory3(1%);
`irritant0;
`allergic9(20%);
`inflammatory8(17%);
`Irritant3(7%);
`
`phenylethanol221(1)
`Chlorobutanol46(3);
`
`allergic23(2%)
`inflammatory70(5%);
`Irritant3(0.2%);
`
`1499(0)
`
`allergic124(5%)
`inflammatory305(11%);
`Irritant65(2%);
`
`allergic42(14%)
`inflammatory9(3%);
`Irritant10(3%);
`
`309(1)
`
`allergic96(19%)
`inflammatory43(9%);
`Irritant19(4%);
`
`allergic-31(7%)
`inflammatory32(7%);
`Irritant37(8%);
`
`438(27)
`
`allergic99(19%)
`inflammatory114(21%);
`Irritant40(8%);
`
`chlorhexidine)
`(chlorobutanol,BAC,
`otherpreservatives
`whencombinedwith
`exhibitssynergisticactivity
`layer;Phenylethanol:
`crossthebacteriallipid
`lipidsolubilityandcan
`Chlorobutanol:increases
`
`fungistaticactivity
`negative;Alsohas
`bacteriaandsomegram
`cocciandgrampositive
`activitymainlyagainst
`andhasantimicrobial
`cytoplasmicmembrane
`permeablelayerofthe
`
`2685(3)
`
`Actsbydestroyingthesemi-
`
`Cl
`
`proteinatesofmercury
`proteinsbyforming
`toprecipitatebacterial
`sulfhydrilgroupsofproteins
`combiningwiththe
`ofthemercuricionby
`sulfur-removingproperties
`
`500(7)
`
`Actasaresultofthe
`
`cytoplasmiclayer
`thesemi-permeable
`membranesanddestroys
`bacterialwallsand
`activitiesbydissolvingthe
`
`593(25)
`
`Actmainlyviadetergent
`
`O
`
`O
`
`Cl
`
`Cl
`
`O
`
`ClOH
`
`phenylethanol
`and
`
`Chlorobutanol
`
`Alcohol
`
`CH
`
`NH
`
`NH
`
`NH
`
`NHNH
`
`NHNH
`
`NHNH
`
`NH
`
`Cl
`
`Hg
`
`S
`
`Chlorhexidine
`
`Amidine
`
`Na+
`
`O−
`
`O
`
`Thimerosal
`
`Organo-mercurial
`
`derivative
`
`Cl−
`
`N+
`
`Structure
`
`BAC
`
`preservative
`used
`Mostcommonly
`
`ammonium
`
`Quaternary
`
`Chemicalclass
`
`Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
`
`

`

`450 Eye allergy
`
`of antigens human leukocyte antigen-DR and clusters of
`designation 23.
`
`Human studies
`Human in-vitro studies performed by Becquet et al. [7]
`showed that unpreserved b-blockers showed no toxic
`effects on cultured human Tenon’s capsule fibroblasts,
`whereas preserved b-blockers showed toxicity and inhi-
`bition of fibroblast proliferation. Mietz et al. [9] also
`demonstrated that instillation of another b-blocker, meti-
`pranolol 0.3% preserved in BAC, produced deterioration
`of the composition of the extracellular matrix and the
`organization of the conjunctival stroma, combined with
`an increase in the number of activated subepithelial
`fibroblasts, in the deposits of collagen and the thickening
`of the basal membrane of the endothelium. In a tissue
`culture model utilizing immortalized corneal and con-
`junctival epithelial cells, toxicity was observed with all
`preservatives, but dependent upon concentration with
`the order of decreasing toxicity observed for thimerosal
`(0.0025%) more than BAC (0.025%) more than chloro-
`butanol (0.25%) more than methylparaben (0.01%) more
`than sodium perborate (0.0025%) [10]. Goto et al. [11]
`performed a study in which human lens epithelial cells
`were cultured in medium containing different dilutions
`of latanoprost, timolol maleate, and BAC and then
`assessed using phase-contrast microscopy after 7 days’
`culture to determine the morphological changes that take
`place. The experiment showed that there is a dose-
`dependent toxic effect of BAC induced by the expression
`of prostaglandin E2 (PGE2), IL-1a and IL-6, resulting in
`the inhibition of the proliferation and elongation of the
`human lens cell and then to cell death.
`
`The effects of preservatives on the eye are sometimes
`obscured by the chronic disease process, for which topical
`ophthalmic medications are used. A study performed by
`Hamard et al. [12] showed that BAC played a role in
`trabecular cell death in glaucoma patients from the
`chronic use of topical ophthalmic medications containing
`BAC. In the study, normal and glaucomatous trabecular
`cell lines were treated for 15 min with antiglaucoma drugs
`(1/100 and 1/10 dilutions): timolol BACþ or BAC,
`betaxolol BACþ or BAC, latanoprost BACþ or pure
`BAC. Apoptotic marker (Apo2.7) expression, annexin V
`binding and DNA content were evaluated by flow cyto-
`metry and confocal microscopy. They found that ben-
`zalkonium-containing b-blockers
`and prostaglandin
`analogue triggered mild expression of one out of three
`apoptotic markers, whereas the proapoptotic effect
`observed with BAC appeared to be largely hindered by
`active compounds in the preserved eyedrops. The use of
`BAC may be worse in patients with more chronic ocular
`disorders as patients with atopic dermatitis had an
`increased sensitivity to preservatives, such as thimerosal,
`parabens, and BAC [5]. However, when actually trying to
`
`assess the impact of BAC in cell-mediated responses, a
`recent study [13] tested 42 898 patients with BAC 0.1% in
`petrolatum (topical drugs, ophthalmics, and disinfectants;
`http://www.ivdk.org) between 1996 and 2006 demon-
`strated 0.6–1.5% reactions with a total of 41 stronger
`positive reactions.
`
`Although human in-vivo studies have generated rare
`reports of BAC induced IgE-mast cell type reactions, a
`recent study [14] demonstrated bronchoconstriction in
`asthmatics when challenged with BAC suggesting a non-
`specific trigger. Specifically relating to the eye, a study by
`Ishibashi et al. [15] evaluated preserved and nonpre-
`served topical timolol and noted that the NIBUT (non-
`invasive breakup time) of the precorneal tear film was
`significantly shortened. They evaluated precorneal tear
`film stability without fluorescein instillation that facili-
`tates the in-vivo noninvasive observation of precorneal
`tear film breakup and found that eye exposure to pre-
`served timolol resulted in significant instability in the
`precorneal tear film at 30 min after instillation, whereas
`the preservative-free timolol had no such effect suggest-
`ing that even a single exposure to 0.005% BAC may
`produce precornealtear film instability.
`
`Thimerosal
`Thimerosal, in its usual concentrations range from 0.001
`to 0.004%, is an organomercurial derivative that acts as a
`result of the sulfur-removing properties of the mercuric
`ion. They act by combining with the sulfhydryl groups of
`proteins to precipitate bacterial proteins by forming
`proteinates of mercury. The proteinates act as a neoanti-
`gen that causes the highest frequency of cell-mediated
`responses of the ophthalmic preservatives [10]. It is most
`commonly found in soft contact lens solutions and may
`cause ocular delayed hypersensitivity.
`
`Animal studies
`In 1991, a study [16] on ocular hypersensitivity to
`thimerosal in rabbits documented that the signs and
`symptoms observed included corneal edema, corneal
`infiltration and erosion,
`infiltration of
`the anterior
`chamber, iritis, conjunctival edema and hyperemia, and
`a significant increase in mucous production. They found
`that the IgG tear antibodies increased as a result of
`increased vascular permeability with the tear IgA titers
`increasing to a lesser extent than IgG during the ocular
`challenge. The major class of serum antibodies consisted
`of IgG, with IgA compromising approximately 5% of
`serum antibodies. Histologic analysis showed that the
`ocular
`inflammatory response was accompanied by
`both polymorphonuclear
`(PMN)
`and mononuclear
`cell infiltrates into the cornea and conjunctiva. Both
`serum and tear antibodies correlate with the severity
`of the ocular inflammatory response and support an
`
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`
`

`

`immune complex mediated or Arthus type of ocular
`hypersensitivity to foreign antigens. In another animal
`study utilizing rat model performed by Becquet et al. [7],
`thimerosal application to the eye resulted in hyperplastic
`changes to the corneo-conjunctival surface with increas-
`ing expression of Limbal class II antibody. In this study,
`anticlass II (RT1b) antibody was found to be the most
`reliable marker to locate and count inflammatory cells.
`
`Human studies
`Thimerosal has demonstrated in a concentration-depen-
`dent manner on human dendritic cells, inhibition of
`lipopolysaccharide (LPS)-induced proinflammatory cyto-
`kines including TNFa, IL-6, and IL-12p70 while having
`no effect on IL-10. These thimerosal-exposed dendritic
`cells induced increased TH2 (IL-5 and IL-13) and
`decreased TH1 (IFNg) cytokine secretion from the T
`cells in the absence of additional thimerosal added to the
`coculture [17]. In addition, there is a potential impact of
`thimerosal on limbal stem cells as documented in a recent
`case report [18].
`
`Tosti and Tosti [3] provides a case report of 36 patients
`with follicular allergic contact conjunctivitis induced by
`thimerosal. All of these patients report using eye drops
`containing thimerosal. Furthermore, 13 patients were soft
`contact lens wearers who became sensitized to their
`contact
`lens solution containing thimerosal. In the
`majority of these cases, the eyelids were spared. But in
`five patients, they also developed an allergic contact
`dermatitis of the eyelids. All of the 36 patients had a
`positive patch test reaction to thimerosal.
`
`Chlorhexidine
`Chlorhexidine is a cationic agent that belongs to the family
`of the bis-diguanides. It is used in the digluconate form,
`and acts by destroying the semi-permeable layer of the
`cytoplasmic membrane and produces its antimicrobial
`activity mainly against cocci and Gram-positive bacteria,
`Gram-negative bacteria as well as fungistatic activity.
`
`Human studies
`Although chlorhexidine has been associated with IgE-
`mast cell mediated reactions, such as anaphylaxis, the
`evidence for localized ocular allergy is lacking [19–22].
`Vaahtoranta-Lehtonen et al. [23] performed an exper-
`iment comparing ethyl-6-O-decanoyl-glucoside 0.005%
`(EDG) combined with 0.00025% chlorhexidine acetate
`(EDGC)
`to a commercial polyaminpropylbiguanide
`(PAPB) used daily as a cleaning and disinfectant agent
`for both ionic and nonionic contact lenses in 59 patients.
`The following symptoms were compared for each
`solution; blurred vision, dryness, foreign body sensation,
`redness, and dirty lenses. The following signs were also
`compared for each solution; conjunctival hyperemia,
`
`Allergy to ophthalmic preservatives Hong and Bielory 451
`
`papillary hypertrophy, corneal deposits, purulence, lim-
`bal vascularization, subepithelial scarring, visual acuity,
`bulbar hyperemia, and tear breakup time. After 8 weeks,
`52% of the participants in the EDGC group showed no
`evidence of corneal or conjunctival abnormalities. In
`contrast, only 19% of the participants in the PAPB group
`showed no abnormalities of the conjunctiva or cornea.
`After 8 weeks, 25% of the EDGC group showed evidence
`of papillary hypertrophy, whereas 50% of the PAPB group
`showed similar findings [23].
`
`In three consecutive cataract operations, chlorhexidine
`was inadvertently used as an intraocular irrigating solution
`as a result of inattentiveness of an assistant. In two of the
`three patients, corneal endothelium damage was so severe
`that penetrating keratoplasty had to be performed. Further
`effects included pronounced iris atrophy, anterior chamber
`applanation, and a retrocorneal membrane. In one case, an
`increase in intraocular pressure developed. No effects
`were observed in the retina or optic nerve [24].
`
`Chlorobutanol and phenylethanol
`Chlorobutanol is an alcohol that acts by increasing lipid
`solubility, and its antimicrobial activity is based on its
`ability to cross the bacterial lipid layer. Chlorobutanol is a
`widely used, very effective preservative in many phar-
`maceuticals and cosmetic products, for example, injec-
`tions, ointments, products for eyes, ears and nose, dental
`preparations, etc. It has antibacterial and antifungal prop-
`erties. Chlorobutanol is typically used at a concentration
`of 0.5% where it lends long-term stability to multi-
`ingredient formulations.
`
`Phenylethanol is an antimicrobial, antiseptic, and disin-
`fectant, which is used also as an aromatic essence and
`preservative in pharmaceutics and perfumery.
`
`Animal studies
`Two drops of a chlorobutanol-containing or BAC-contain-
`ing artificial tear were instilled into the right eye of six
`rabbits. At the same time six control animals received no
`eyedrops. The central region of the corneal epithelium was
`quantitatively assessed using a computer system. There
`were up to 5% exfoliating cells evident at the ocular surface
`in treated rabbits but with no difference between the two
`products. Controls had no cell exfoliation (<0.5%). The
`distribution of surface areas of the squamous cells in the
`treated eyes was shifted to slightly larger values than in
`the controls after use of the chlorobutanol-containing
`product but the number of epithelial cell craters/cell
`was unchanged from that of the controls. Cell surface areas
`were shifted to significantly smaller values than controls
`after use of the BAC-containing product and there were
`much fewer epithelial cell craters/cell. The results reveal
`differences in the effects of preservative-containing
`
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`
`

`

`452 Eye allergy
`
`artificial tears on the squamous cells of the corneal
`epithelium in a clinically relevant situation [25].
`
`Human studies
`Human in-vitro studies have been reported by Tripathi
`and Tripathi [26] who evaluated the cytotoxicty of BAC
`and chlorobutanol by exposing primary cultures of human
`corneal epithelial cells to a single dose of each preserva-
`tive. Control and experimental cultures were analyzed by
`continuous time-lapse videomicrographic recordings as
`well as by sequential phase-contrast microscopy. Both
`BAC at a concentration of 0.01% and chlorobutanol at
`0.5% caused immediate cessation of normal cytokinesis
`and mitotic activity, and epithelial cells degenerated
`within 2 and 8 h, respectively. A more recent version
`of this experiment demonstrated that the survival of
`corneal and conjunctival epithelia in culture with pre-
`servatives polysorbate and benzalkonium were highly
`cytotoxic with cell survival decreasing to 20% at the
`concentration estimated in commercial ophthalmic
`solutions as compared with 80% survival of cells exposed
`to chlorobutanol [27]. Although there have been limited
`human in-vivo studies that demonstrate any immediate
`reactivity through an IgE-mast cell mediated mechanism,
`Garcia-Medina et al. [28] describes a case of a woman who
`presented with intense ocular pruritus and conjunctival
`hyperemia with each instillation of Cloircusi fluotest
`(Alcon, El Masnou, Spain), containing chlorobutanol.
`Skin tests were all negative. Chlorobutanol was presumed
`as the reagent through elimination and positive conjunc-
`tival provocation test with purified chlorobutanol con-
`firmed the hypothesis [28].
`
`Parabens
`Parabens are esters of p-hydroxybenzoic acid. They act by
`targeting molds and fungi rather than bacteria. In an
`assessment of preservative sensitivity in the United King-
`dom, the results of patch testing using the extended British
`Contact Dermatitis Society Standard series, they found
`that parabens mix has the highest irritancy rate [29].
`
`Animal studies
`Becquet et al. [7] showed alteration of the rat conjunctival
`surface after 1 month of treatment with instillation of eye
`drops containing 0.05% methyl parahydroxybenzoate
`with increased number of epithelial cell layers, loss of
`goblet cells, and appearance of keratinization of the most
`superficial cell layers.
`
`Human studies
`There are few human studies performed recently
`because of their well established role in delayed hyper-
`sensitivity. Nagel et al. [30] presents a case report of
`bronchospasm and pruritus when a hydrocortisone prep-
`aration containing methylparaben and propylparaben is
`
`given intravenously to an asthmatic patient. Adminis-
`tration of the hydrocortisone preparation without the
`paraben preservative did not elicit the same response.
`Skin tests for immediate hypersensitivity to parabens
`were positive. They were able to conclude that parabens
`are capable of producing immunologically mediated,
`immediate systemic hypersensitivity reactions. Henry
`et al. [31] also describes the relationship of parabens
`and the development of contact urticaria.
`
`Preservatives and complications of chronic
`treatment
`The toxicity of preservatives manifest with prolonged use
`in the chronic treatment of ocular diseases. The cytotoxic
`effects increase with the concentration of the preservative
`and the duration of the exposure. As the widespread use of
`preservatives in many commonly used products continues,
`more studies such as those with contact lens formulations
`and ocular allergy treatments (as the ocular allergy ther-
`apeutic market has continued to increase by 10–20% per
`annum) will have to be done to study its effects [32],
`especially those that are adverse and compromise the
`safety of the consumer in order to better define the toxic
`from the immunologic/allergic adverse effects.
`
`Conclusion
`Many topical ophthalmic agents use preservatives as they
`are designed for ‘multiuse’ treatment regimens. Many
`clinicians commonly refer to the induction of the signs
`and symptoms of itchy, burning, gritty (dolor), red
`(rubor), and swollen (tumor) as an ‘allergy’. In actuality,
`it appears that many of these forms of ‘allergic conjunc-
`tivitis’ are associated with the continuous administration
`of the preservative in constant contact with the conjunc-
`tival surface and not a true allergy to the drug. Preserva-
`tives are present in almost all ophthalmic preparations
`and play an important role as they may cause adverse side
`effects, from mild irritation to severe toxic reactions.
`Continued study on the effects of these preservatives
`and other inactive ingredients is important to ensure that
`the therapeutic result of the ophthalmic preparations is
`not diminished by the adverse effects that preservatives
`may produce in the patient.
`
`References and recommended reading
`Papers of particular interest, published within the annual period of review, have
`been highlighted as:
`
`of special interest
` of outstanding interest
`Additional references related to this topic can also be found in the Current
`World Literature section in this issue (pp. 486–487).
`
`1 Wilson FM 2nd. Allergy to topical medications. Int Ophthalmol Clin 2003;
`43:73–81.
`
`2
`
`Uter W, Menezes de Padua C, Pfahlberg A, et al. Contact allergy to topical
`ophthalmological drugs: epidemiological risk assessment. Klin Monatsbl
`Augenheilkd 2009; 226:48–53.
`
`Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
`
`

`

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`16 Baines MG, Cai F, Backman HA. Ocular hypersensitivity to thimerosal
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`Kilp H. The dry eye and contact lens. Fortschr Ophthalmol 1986; 83:125.
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`Pellinen P, Lokkila J. Corneal penetration into rabbit aqueous humor is
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`dose (30 ml), the maximum concentrations at 45 min of tafluprost acid in aqueous
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`served tafluprost indicating that BAC does not affect corneal penetration in rabbit
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`
`7
`
`8
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`Becquet F, Goldschild M, Moldovan MS, et al. Histopathological effects of
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`10
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`Epstein SP, Ahdoot M, Marcus E, Asbell PA. Comparative toxicity of pre-
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`A study that is currently in the process of publication found that the order of
`decreasing toxicity at
`the most commonly used concentrations:
`thimerosal
`(0.0025%) more than BAC (0.025%) more than chlorobutanol (0.25%) more
`than methyparaben (0.01%) more than sodium perborate (0.0025%) approxi-
`mately EDTA (0.01%). The study was performed using a tissue culture model
`utilizing immortalized corneal and conjunctival epithelial cells and evaluating the
`potential toxicity of these common components and their comparative effects on
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`some degree of ocular tissue damage.
`
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`12 Hamard P, Blondin C, Debbasch C, et al. In vitro effects