Clinical Ophthalmology
`
`Open Access Full Text Article
`
`Dovepress
`
`open access to scientific and medical research
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`REvI Ew
`
`Development of a non-settling gel formulation
`of 0.5% loteprednol etabonate for anti-
`inflammatory use as an ophthalmic drop
`
`Martin J Coffey1
`Heleen H DeCory2
`Stephen S Lane3
`1Pharmaceutical Product
`Development, Bausch and Lomb, Inc,
`Rochester, NY, USA; 2Global Medical
`Affairs, Pharmaceuticals, Bausch
`and Lomb, Inc, Rochester, NY, USA;
`3Associated Eye Care, Stillwater, MN,
`USA
`
`Correspondence: Martin J Coffey
`Pharmaceutical Product Development,
`Bausch and Lomb, Inc, 1400 N Goodman
`St, Rochester, NY 14607, USA
`Tel +1 585 338 6679
`Fax +1 585 338 0737
`Email martin.coffey@bausch.com
`
`Abstract: The eye has protective barriers (ie, the conjunctival and corneal membranes) and
`defense mechanisms (ie, reflex tearing, blinking, lacrimal drainage) which present challenges
`to topical drug delivery. Topical ocular corticosteroids are commonly used in the treatment of
`anterior segment diseases and inflammation associated with ocular surgery, and manufacturers
`continually strive to improve their characteristics. We describe the development of a novel
`ophthalmic gel formulation of loteprednol etabonate (LE), a C-20 ester-based corticosteroid with
`an established safety profile, in the treatment of ocular inflammatory conditions. The new LE gel
`formulation is non-settling, eliminating the need to shake the product to resuspend the drug, has
`a pH close to that of tears, and a low preservative concentration. The rheological characteristics
`of LE gel are such that the formulation is instilled as a drop and transitions to a fluid upon
`instillation in the eye, yet retains sufficient viscosity to prolong ocular surface retention. The new
`formulation provides consistent, uniform dosing as evidenced by dose extrusion studies, while
`pharmacokinetic studies in rabbits demonstrated rapid and sustained exposure to LE in ocular
`tissues following instillation of LE gel. Finally, results from two clinical studies of LE gel in the
`treatment of postoperative inflammation and pain following cataract surgery indicate that it was
`safe and effective. Most patients reported no unpleasant drop sensation upon instillation, and
`reports of blurred vision were rare.
`Keywords: loteprednol etabonate, gel, drug delivery, clinical trial, ocular surface
`
`Topical corticosteroids are commonly prescribed in ophthalmology for the treatment
`of anterior segment inflammation due to their broad anti-inflammatory effects. For
`instance, they inhibit prostaglandin and leukotriene synthesis through inhibition of
`phospholipase A2 by promoting the synthesis of lipocortins that block phospholipase
`A2; they suppress capillary dilation, inhibit macrophage and neutrophil migration, and
`reduce T cells and B cells responsible for the inflammatory response; and they also
`stabilize intracellular and extracellular membranes.1,2 Corticosteroids mediate their
`effects primarily by binding to and modifying the activity of cytosolic glucocorticoid
`receptor (GR) at the genomic level.1,3,4 Corticosteroids bind to the GR in the
`cytoplasm, after which the corticosteroid-GR complex migrates to the nucleus and
`inhibits the expression of pro-inflammatory proteins while inducing the expression of
`anti-inflammatory proteins. The corticosteroid-GR complex also elicits non-genomic
`effects, such as inhibition of vasodilation, vascular permeability, and migration of
`leukocytes.2,4 In addition, corticosteroids mediate non-genomic anti-inflammatory
`effects by binding to membrane-bound GRs and through direct nonspecific interactions
`with cellular membranes.2,5
`
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`http://dx.doi.org/10.2147/OPTH.S40588
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`Clinical Ophthalmology 2013:7 299–312
`© 2013 Coffey et al, publisher and licensee Dove Medical Press Ltd. This is an Open Access article
`which permits unrestricted noncommercial use, provided the original work is properly cited.
`
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`This article was published in the following Dove Press journal:
`Clinical Ophthalmology
`12 February 2013
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`Table 1 Physical properties and composition of normal tear
`fluid11,13–16
`
`Characteristic
`
`Composition
`
`Proteins
`and enzymes
`
`Typical
`range
`7.3–7.5
`Physical properties pH
`300–350
`Osmolality (mOsm)
`1.3–5.9
`viscosity (cps)
`Surface tension (dynes/cm2) 40–50
`Sodium (mmol/L)
`Potassium (mmol/L)
`Chloride (mmol/L)
`Bicarbonate (mmol/L)
`Calcium (mmol/L)
`Total nitrogen (mmol/L)
`Me bomian oils (g/L)
`Total protein (g/L)
`Albumin (g/L)
`Lysozyme (g/L)
`Lactoferrin (g/L)
`
`Mean
`value
`7.4
`320
`2.9
`45
`146 ± 10
`16 ± 5
`128 ± 5
`26
`0.57
`113
`1.3
`8
`3.94
`1.7
`2.75
`
`20–40
`
`4.3–12.2
`
`Despite the availability of numerous topical
`corticosteroid preparations, there is a continued need to
`modify the formulations for improved ocular delivery
`into the anterior segment. We describe the development
`of loteprednol etabonate (LE) in a novel ophthalmic gel
`formulation for improved ocular delivery. The LE gel
`formulation has attributes intended to provide consistent
`dose uniformity, without the need to shake, and increased
`residence time of the drug on the ocular surface, as well
`as attributes intended to provide greater comfort for the
`patient. We begin with a brief review of the barriers to
`anterior segment delivery of a topically applied drug,
`before describing the development of LE in the novel gel-
`based formulation.
`
`Barriers to topical ocular drug
`delivery
`Topical ocular drug delivery is the preferred route for
`treating anterior segment diseases and inflammation
`associated with cataract and refractive surgery. Direct
`application of a small dose to the ocular surface typically
`provides a fast onset of action at the anterior segment
`with minimal systemic exposure. Tear fluid secretion, tear
`volume, and lacrimal drainage present the first barriers
`to topical ocular drug delivery.6,7 The anterior surface of
`the eye is continuously rinsed by tear fluid secreted by the
`lacrimal glands and the goblet cells. The basal secretion
`rate for tear fluid is about 1.2–1.5 µL/min, while the
`normal tear volume on the surface of the eye is about
`6–7 µL.7–9 At steady state, this means that the tear fluid
`has a mean residence time (τ = V/kdr) of 5–6 minutes on
`the surface of the eye. Instillation of a topical drop will
`increase the volume of liquid on the surface of the eye to a
`maximum capacity of about 25–30 µL as the formulation
`is mixed with the tear fluid.7,10 Excess fluid beyond the
`maximal capacity will overflow at the lacrimal lake or
`be splashed onto the eyelashes by reflex blinking, while
`nasolacrimal drainage will quickly return tear volume back
`to normal.6,11 Moreover, if the physical characteristics of the
`post-instillation tear fluid mixture cause any irritation or
`discomfort (eg, foreign body sensation, pH outside of the
`normal range, or osmolality outside of the 200–600 mOsm
`range), reflex tearing, reported to increase to as high
`as 300–400 µL/min, and reflex blinking will contribute
`further to lacrimal lake overflow and the dilution and loss
`of drug via nasolacrimal drainage.6,11,12 The approximate
`composition and properties of normal tear fluid are
`outlined in Table 1. The cornea is highly innervated,
`
`providing immediate feedback to the lacrimal glands and
`the muscles controlling blinking in the event that tear fluid
`composition is altered. As a consequence, most aqueous
`formulations have extremely short residence times on the
`surface of the eye. Common formulation approaches to
`prolong ocular residence time and enhance drug delivery
`include the use of viscous aqueous formulations (ie, gels),
`which thicken the tear fluid and reduce the tear fluid
`drainage rate from the surface of the eye, and ointment
`formulations, which are not miscible with the tear fluid and
`therefore also slow the removal of the formulation from
`the surface of the eye.
`The site of action for most topically applied drugs includes
`the tissues of the anterior segment – the cornea, conjunctiva,
`sclera, and iris-ciliary body. Drug penetration into the iris-
`ciliary body, of importance in the treatment of postoperative
`inflammation, is dependent on prior drug penetration through
`the cornea into the aqueous humor and/or penetration
`through the sclera followed by absorption into the iris-ciliary
`body. The cornea offers the major pathway for drug diffusion
`into the anterior chamber of the eye, especially for small
`molecules. Small lipophilic compounds generally penetrate
`through the epithelium via the intracellular route, while small
`hydrophilic compounds are limited to the paracellular route.
`The fraction of a lipophilic compound penetrating through
`the cornea is 20 times greater than a hydrophilic molecule of
`similar molecular size.17 A logD (log distribution coefficient
`at pH 7.65) of 2–3 for beta blockers was reported to provide
`optimal corneal permeation.18 Permeation through the
`conjunctival epithelium is limited by the tight junctions. The
`high conjunctival surface area of diffusion when compared
`
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`Development of loteprednol etabonate gel
`
`with the cornea (17:1) contributes to the importance of
`this route especially for hydrophilic compounds and large
`molecules.19 However, unlike the cornea, the sclera and
`conjunctiva are vascularized tissues. The presence of blood
`vessels in the conjunctiva can limit drug penetration to the
`sclera, carrying drug instead to the systemic circulation.7,10
`Compounds penetrating through the conjunctiva can continue
`passage into the eye through the sclera. Scleral permeation
`does not depend on the compound lipophilicity, but has
`been reported to be inversely proportional to the molecular
`radius.20 Drug molecules can be cleared directly from the
`aqueous humor through the aqueous humor drainage as well
`as through the blood vessels penetrating the vascularized
`tissues.
`For topical ocular drugs that are neither charged nor
`are weak acids or bases (eg, corticosteroids), absorption
`follows Fick’s first law of diffusion – namely, the rate of drug
`penetration across or into ocular anterior segment tissues is
`proportional to the drug concentration in the tear fluid and
`the permeability of the drug through the ocular tissues.
`Given that drug delivery to the ocular surface is limited
`by tear fluid secretion and turnover, it is not surprising that
`only 5% or less of a topically applied drug is estimated to
`penetrate the cornea and reach intraocular tissues.6 It follows
`that ocular therapy could be improved if the ocular surface
`residence time of a drug were increased without causing
`discomfort to the patient’s eye.
`
`Properties of loteprednol etabonate
`LE is an ester-based corticosteroid commonly prescribed
`for the topical treatment of various ocular inflammatory
`diseases as well as inflammation occurring after cataract
`surgery. Approved by the US Food and Drug Administration
`in 1998 in an aqueous suspension formulation (Lotemax®;
`
`Bausch and Lomb Incorporated, Rochester, NY, USA),
`LE differs from traditional corticosteroids in that it contains
`an ester group at the carbon 20 (C-20) position of the
`corticosteroid core structure in lieu of a ketone. Specifically,
`LE is a 17β-chloromethylester derivative of ∆1-cortienic
`acid, an inactive metabolite of prednisolone; LE also has
`a 17α-etabonate moiety (Figure 1). The ester substitution
`was the result of retrometabolic drug design, in which novel
`drugs are designed such that they are converted into inactive
`metabolites after exerting their therapeutic effects, thereby
`avoiding unwanted adverse effects.21,22 For ophthalmic use
`of corticosteroids, the primary side effect of concern is
`increased intraocular pressure (IOP),23 which is thought
`to result from structural and biochemical changes on the
`trabecular meshwork induced by corticosteroids, leading to
`increased resistance to aqueous outflow.24,25 As a function of
`its retrometabolic design, any LE not bound to GRs is rapidly
`metabolized to inactive carboxylic acid metabolites by tissue
`esterases (Figure 1), resulting in a decreased effect on IOP
`relative to traditional C-20 ketone corticosteroids.
`In addition to increased IOP, corticosteroids are also
`associated with the potential for cataract formation.23
`The presence of an ester function at the C-20 position in
`the LE molecule has the added advantage of decreased
`potential for cataractogenicity. Manabe et al demonstrated
`that topical corticosteroids such as prednisolone form
`Schiff base intermediates with lens proteins, a first step in
`cataractogenesis, through the ketone moiety at the C-20
`position.26 However, non-ketolic analogs are not able to form
`such adducts. LE is a non-ketolic C-20 ester corticosteroid,
`and presumably is also unable to form such adducts, although
`other mechanisms of cataractogenesis cannot be ruled out.
`LE has been shown to have the right balance of
`lipophilicity to aqueous solubility required for effective ocular
`
`C-20 ester
`function
`
`
`
`O
`
`Cl
`
`
`O
`
`O
`
`O
`
`O
`
`HO
`
`O
`
`OH
`
`O
`
`HO
`
`O
`
`"
`
`O
`
`HO
`
`O
`
`OH
`
`OH
`
`O
`
`O
`
`O
`
`Loteprednol
`etabonate
`
`∆1- cortienic acid
`etabonate
`
`∆1-cortienic acid
`
`Figure 1 Molecular structure of loteprednol etabonate and metabolism of loteprednol etabonate to inactive metabolites.
`Notes: Loteprednol etabonate has an ester function at C-20 position and is metabolized by esterases to ∆1-cortienic acid etabonate and then to ∆1-cortienic acid. Both
`metabolites lack glucocorticoid activity.
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`tissue penetration. The lipophilicity of LE and other steroids
`was calculated according to their retention characteristics
`by reversed phase high pressure liquid chromatography
`(HPLC). The lipophilicity of LE (log K = 3.04) was found
`to be seven times greater than that of dexamethasone (log
`K = 2.19).27 While its water solubility is relatively low
`(0.5 µg/mL), early studies demonstrated that its solubility
`could be increased by inclusion of solubilizing agents
`(eg, propylene glycol or cyclodextrin) and permeability
`enhancers in the formulation.27 Druzgala et al were the first
`to demonstrate that LE readily penetrates ocular tissues.28
`Instillation of 14C-labelled LE (three 50-µL drops of 0.5%
`LE in a 1% hydroxypropyl methylcellulose test formulation
`at 5-minute intervals) in the eyes of rabbits led to high
`concentrations in the conjunctiva and cornea, followed by the
`iris–ciliary body and aqueous humor, at 30 minutes following
`instillation. The authors attributed the relatively low aqueous
`humor concentration to the rapid metabolism of unbound LE
`to inactive metabolites by esterases. Inactive metabolites of
`LE were found in all three tissues, with the highest ratio of
`metabolites to unchanged drug in the cornea, suggesting that
`the cornea is the primary site for metabolism. More recently,
`Glogowski and Proksch studied the ocular tissue penetration
`of LE following instillation of a single 50-µL drop of either
`the 0.5% marketed suspension formulation (povidone-based)
`or ointment formulation in rabbits with corneal inflammation
`and likewise found high concentrations in the conjunctiva
`and cornea and low levels in the aqueous humor.29 Maximal
`concentrations (Cmax) in the conjunctiva, cornea, and aqueous
`humor were 7.77, 3.00, and 0.06 nmoles/g, respectively,
`following instillation of the suspension formulation and
`
`4.41, 2.48, and 0.16 nmoles/g, respectively, following
`instillation of the ointment formulation.29 In both studies,
`the concentration–time profile of LE in the aqueous humor
`closely paralleled that in the cornea, suggesting that LE in the
`aqueous humor originates primarily from the cornea.
`Preclinical research showed that LE has a high affinity
`for the cytosolic GR, an affinity 4.3 times stronger than
`that of dexamethasone, when tested in rat lung type II GR
`binding studies.30 Additional preclinical studies by Bodor
`and colleagues, reviewed in 2000 by Bodor and Buchwald,
`showed that the therapeutic index of LE was more than
`20-fold better than that of other corticosteroids including
`hydrocortisone 17α-butyrate, betamethasone 17α-valerate,
`and clobetasone 17α-propionate, based on the cotton pellet
`granuloma test and thymolysis potency.22 Thus, LE was
`predicted to have potent anti-inflammatory activity along
`with decreased side-effect potential.
`Clinical studies demonstrated the efficacy and safety
`of LE in a suspension formulation for the treatment of
`numerous ocular inflammatory conditions including, but not
`limited to, anterior uveitis, giant papillary conjunctivitis, and
`seasonal allergic conjunctivitis,31–35 and in both suspension
`and ointment formulations in the treatment of inflammation
`and pain following cataract surgery.36–38 Consistent with its
`retrometabolic design, the incidence of clinically significant
`elevations in IOP ($10 mmHg) was similar between
`LE-treated patients and vehicle-treated patients in most
`studies and less than that observed in prednisolone-treated
`patients.39,40 Additional safety studies, including studies in
`steroid responders, demonstrated a significant difference in
`the incidence of IOP elevation in favor of LE compared with
`
`Steroid, anti-inflammatory
`
`Table 2 Comparison of 0.5% loteprednol etabonate suspension and gel formulations
`Ingredients
`Function
`Active substance
` Loteprednol etabonate
`Excipients
`Suspending and/or viscosity-increasing agent
`Povidone
`Suspending and/or viscosity-increasing agent
`Polycarbophil
`Tonicity agent/humectant
`Glycerin
`Tonicity agent/humectant
`Propylene glycol
`Tonicity agent
`Sodium chloride
`Buffer/antimicrobial enhancer
`Boric acid
`Surfactant and/or wetting agent
`Tyloxapol
`Chelant/antimicrobial enhancer
`Edetate disodium dihydrate
`Antimicrobial preservative
`Benzalkonium chloride
`pH adjuster
`Sodium hydroxide and/or HCl
`vehicle
` water for injection
`Note: The + sign indicates the presence of excipient in the formulation.
`Abbreviations: LE, loteprednol etabonate; ppm, parts per million; qs, sufficient quantity.
`
`LE suspension 0.5%
`
`LE gel 0.5%
`
`5.00 mg/mL
`
`5.00 mg/g
`
`+
`
`+
`
`+
`+
`100 ppm
`qs to pH 5.5
`qs to 1 mL
`
`+
`+
`+
`+
`+
`+
`+
`30 ppm
`qs to pH 6.5
`qs to 1 g
`
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`Development of loteprednol etabonate gel
`
`the C-20 ketone steroids prednisolone, dexamethasone, and
`fluorometholone.40–45
`
`A non-settling gel formulation
`of loteprednol etabonate 0.5%
`Current marketed formulations of LE 0.5% include a
`suspension (Lotemax®) and an ointment (Lotemax®
`ointment). The LE suspension formulation is a low viscosity
`suspension containing povidone and glycerin, both sometimes
`used as active ingredients for the relief of dry eye symptoms
`in over-the-counter products.46 It is preserved with 0.01%
`benzalkonium chloride (BAK), a quaternary ammonium
`preservative widely used in ophthalmic formulations for its
`potent antimicrobial efficacy and chemical stability. Despite
`its established efficacy, a drawback of the LE suspension
`formulation, or any other steroid suspension formulation,
`is the need to shake vigorously prior to dosing to assure
`a consistent dose of medication. In a study of patient
`compliance, Apt et al showed that less than one-third of
`patients shake their topical ophthalmic medication prior
`to instillation,47 underscoring the benefit of developing
`non-settling formulations. While ointment formulations
`do not need to be shaken, the LE ointment formulation has
`disadvantages common to all ophthalmic ointments – namely,
`blurred vision, due to refractive index difference between the
`tears and the ointment, and the potential for inaccurate dosing
`due to difficulty instilling a precise ribbon of ointment.48
`The newly developed ophthalmic gel formulation of
`LE 0.5% provides sufficient structure such that LE stays in
`suspension and the formulation does not need to be shaken
`prior to dosing. LE 0.5% gel behaves as a semisolid gel in
`the bottle, shear-thins to a liquid when being dispensed from
`the dropper bottle, and converts to a liquid when mixed
`with tear fluid on the surface of the eye, while maintaining
`sufficient viscosity for ocular surface retention. All gels have
`a measurable yield stress (in Pascal [Pa]), or minimum stress
`that must be applied to initiate flow. Until a force greater
`than the yield stress is applied to the gel, it will not flow,
`and hence, particles in suspension will not settle. In the case
`of LE gel, when the bottle is tipped and squeezed, the force
`applied exceeds the yield stress and the gel is able to flow,
`like a liquid, and be expressed as a drop. LE gel has also
`been formulated in such a way as to result in minimal visual
`distortion compared with other ophthalmic gels, due to the use
`of a gelation polymer that becomes significantly less viscous,
`transitioning to a fluid after mixing with tears in the eye. This
`stands in contrast to so-called in situ gel-forming solutions
`which are designed to transition from a solution to a gel upon
`
`instillation in the eye and mixing with tears (eg, Timoptic-XE;
`[Merck and Co, Inc, Whitehouse Station, NJ, USA] and the
`generic Timolol Gel Forming Solution [Timolol GFS]). The
`composition of the new LE ophthalmic gel is compared with
`the LE suspension in Table 2. The gel formulation replaces
`the povidone suspending agent with polycarbophil. It is the
`polycarbophil polymer that provides the gel structure to the
`formulation to prevent sedimentation of LE. Polycarbophil
`also functions as a mucoadhesive and viscoelastic suspending
`agent. The specific level of polycarbophil in the formulation
`provides a sufficient yield stress to prevent settling of the LE
`in the dropper bottle but also provides viscosity low enough
`to allow delivery as a drop when the bottle is squeezed. From
`a clinical perspective, the new non-settling LE gel formulation
`is expected to deliver consistent, full doses of LE to the ocular
`surface for reliable drug delivery and subsequent clinical
`effect. For patients, these attributes translate into a formulation
`that does not need to be shaken prior to instillation, not unlike
`an ointment, yet having a delivery ease and simplicity similar
`to that of an aqueous drop formulation, and without expected
`blurred vision.
`Rheology studies demonstrated that LE gel behaves as
`a semisolid gel at low shear and a fluid-like suspension at
`high shear.49 Figure 2 shows the viscosity of the LE gel as
`a function of applied shear stress. Below a yield stress of
`4 Pa, the gel does not flow and, hence, allows no settling
`or sedimentation of drug particles. At higher shear stress
`(ie, .30 Pa), the viscosity is less than 0.1 Pa ⋅ s or 100
`centipoise (cps) and the product can be easily expressed as
`a liquid drop through a dropper tip. The conversion from
`a gel at rest to a liquid under high shear and back to a gel
`at low shear was found to occur in less than one second.49
`Because the gel adapts to different shear forces almost
`instantaneously, LE particle sedimentation will not occur
`during use of the formulation. Figure 3 illustrates how, after
`delivery from the dropper bottle, LE gel immediately regains
`a gel structure, remaining at the site of delivery. In contrast,
`the lower viscosity of LE suspension causes it to flow away
`from the administration point.
`LE gel rheological characteristics were reflected in
`sedimentation studies. The concentration of LE suspended
`in the unshaken gel following 16 months of stability
`testing (upright storage at 25°C and 40°C) ranged from
`100.4%–107.6% of label and did not differ whether sampled
`near the top or near the bottom of the bottled test samples.49
`Furthermore, LE did not sediment out of the gel formulation
`under accelerated conditions. Figure 4 presents the visual
`sedimentation results following exposure of LE suspension
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`Development of loteprednol etabonate gel
`
`LE suspension
`
`LE gel
`
`Figure 3 Delivery of LE 0.5% suspension and LE 0.5% gel from the dropper bottle.
`Notes: Both formulations were delivered as an eyedrop to a glass plate (held at
`a 45 degree angle). After delivery, the gel formulation immediately regained its
`gel structure and remained where it was delivered. In contrast, the suspension
`formulation flowed away from the administration point. Photograph taken
`immediately after administering the drop of LE 0.5% suspension and approximately
`1 minute after administering the drop of LE 0.5% gel.
`Abbreviation: LE, loteprednol etabonate.
`
`with tears, is expected to increase the ocular surface contact
`time of the formulation, potentially increasing bioavailability.
`Thus, even after mixing with tears, the polycarbophil in the
`tear fluid mixture continues to affect viscosity. Figure 6
`compares the viscosity of LE gel formulation with that
`of the current LE suspension and ointment formulations
`at low shear rates before and after dilution with tear fluid.
`Undiluted LE gel has a viscosity much greater than that of
`the LE suspension formulation but lower than that of the
`LE ointment formulation (Figure 6A). Diluting LE gel with
`simulated tear fluid at a ratio of 3:1 (the ratio expected when
`a normal drop is instilled in the eye and mixes with tear
`fluid) resulted in the LE gel transitioning to a mucoadhesive
`fluid with viscosity higher than that of the LE suspension
`formulation (Figure 6B) but low enough to prevent any
`potential discomfort to the patient.
`The pH of the LE gel formulation has been adjusted to
`be closer to that of normal tears (pH 7.4), from 5.5 in the LE
`suspension formulation to 6.5 in the LE gel formulation. For
`many patients, the natural buffering capacity of tears, mainly
`due to dissolved carbon dioxide and bicarbonate, will readily
`accommodate this small difference in pH with little noticeable
`difference. The osmolality of LE gel, 280–300 mOsm, is
`consistent with that of normal tear fluid (302–350 mOsm)11,13
`and has been reported by patients to be comfortable.
`As a further improvement, the concentration of BAK
`required to provide antimicrobial preservation has been
`reduced by 70%, from 0.01% (100 ppm) in the LE suspension
`
`LE suspension
`
`LE gel
`
`LE gel layered
`over gel vehicle
`
`Figure 4 Sedimentation of LE 0.5% suspension and LE 0.5% gel formulations under 120× g at 1000 rpm (116–145× g) for 24 hours using a LUMiSizer dispersion analyzer
`(LUM GmbH, Berlin, Germany).
`Notes: LE particles settled out of suspension within 20 minutes from the suspension formulation while remaining suspended in the gel formulation. Even when the LE 0.5%
`gel formulation was placed above additional placebo vehicle (clear), LE particles did not migrate under centrifugation.
`Abbreviation: LE, loteprednol etabonate.
`
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`with $2 log kills at 6 hours and $3 log kills by 24 hours,
`while also producing $2 log reductions in fungi at
`7 days (Bausch and Lomb, Inc., data on file, 2012).
`The LE gel formulation contains both glycerin and
`propylene glycol. Glycerin and propylene glycol are listed
`as over-the-counter ocular lubricants for treatment of dry
`eye.46 These ingredients also function as humectants to retain
`moisture on the surface of the eye53 and are expected to
`contribute to patient comfort. Formulated together, glycerin
`and propylene glycol have been found to perform better than
`either humectant agent alone.56 The glycerin and propylene
`glycol also act as tonicity agents, contributing to the final
`osmolality of 280–300 mOsm.
`Glogowski and Jiang evaluated the ocular and systemic
`pharmacokinetics of LE gel following a single 35-µL
`topical ocular instillation in healthy rabbits.57 LE was rapidly
`absorbed and distributed within the eye, with measurable
`concentrations observed in ocular tissues within 5 minutes
`after dosing. Maximal concentrations (Cmax) of LE were
`achieved within 0.5 hours in ocular tissues following a
`single, topical ocular dose with minimal levels in the plasma.
`Maximum concentrations of LE were highest in tear fluid
`(3.34 µmol/g), followed by bulbar conjunctiva (8.63 nmol/g),
`cornea (4.67 nmol/g), iris/ciliary body (0.35 nmol/g), and
`aqueous humor (0.03 nmol/mL), with a mean residence time
`of more than 9 hours in both the bulbar conjunctiva and cornea.
`Thus, it appears that formulating LE in a polycarbophil-based
`gel led to an increase in the Cmax of LE in conjunctival and
`corneal tissues of approximately 10% and 50%, respectively,
`compared with the less viscous LE suspension formulation.
`Perhaps more importantly, the overall exposure, as measured
`by the area under the concentration time curve from 0 to
`24 hours (AUC(0–24)) for conjunctival tissue and cornea was
`39.0 nm ⋅ h/g and 11.6 nm ⋅ h/g, respectively, with the new LE
`gel formulation compared with 13.1 nm ⋅ h/g and 7.07 nm ⋅ h/g
`for the LE suspension formulation, representing a 200% and
`65% increase in penetration into these tissues, respectively.
`These data suggest that the increased viscosity of the LE
`gel–tear fluid mixture due to polycarbophil may indeed provide
`greater ocular surface contact time for increased bioavailability.
`Because the tear fluid turnover rate in rabbits is about half that
`reported in humans (0.53 µL/min versus 1.2 µL/min),58 it has
`been reported that rabbit models may underestimate the benefit
`of viscosity increases on retention and drug delivery of topical
`ophthalmic formulations.59,60 It follows that the improvement
`in ocular surface contact time with LE gel may be even greater
`in humans. While these results are promising, head to head
`pharmacokinetic studies comparing the LE gel formulation
`
`B
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`250
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`200
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`150
`
`100
`
`50
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`LE per drop (µg)
`
`Coffey et al
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`45
`
`40
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`35
`
`30
`
`25
`
`20
`
`A
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`Drop weight (mg)
`
`Unshaken
`bottles
`
`Shaken
`bottles
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`Unshaken
`bottles
`
`Shaken
`bottles
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`0123456
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`C
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`µg/mg
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`Unshaken
`bottles
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`Shaken
`bottles
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`Figure 5 Drop weight (A), amount of dose delivered per drop (B), and resulting
`drop potency (C) of a representative lot of LE 0.5% gel.
`Notes: Data represent the mean ± standard deviation for three test bottles, with
`six individual drops expressed per bottle. Bottles that were shaken were inverted
`ten times in rapid succession immediately prior to drop expression.
`Abbreviation: LE, loteprednol etabonate.
`
`formulation to 0.003% (30 ppm) in the LE gel formulation.
`BAK has been reported to be toxic in static cell cultures.51,52
`Although there is ongoing controversy about the relevance
`of these in vitro findings to the clinical setting, the amount
`of BAK added to the LE gel formulation has been reduced
`by inclusion of boric acid (buffering agent) and disodium
`edetate (EDTA, a chelant) in the formulation. While neither
`boric acid nor EDTA provides preservation on its own, both
`are able to enhance the preservation provided by the lower
`concentration BAK. Ophthalmic products sold in the United
`States and Japan are required to demonstrate antimicrobial
`activity against pathogenic bacterial test organisms and
`stasis against fungal organisms.53,54 The requirements in
`Europe are more stringent and require a measurable level
`of antifungal efficacy as well.55 The LE gel formulation was
`evaluated against the more stringent preservative efficacy
`requirements as outlined in Europe and found to pass
`European Pharmacopoeia A standards, with a concentration
`of 30 ppm of BAK. Specifically, LE gel containing 30 ppm
`BAK reduced all required bacterial challenge organisms
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`Clinical Ophthalmology 2013:7
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`Eye Therapies Exhibit 2037, 8 of 14
`Slayba