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`Suegnatronal journaf of pharm.
`‘ General Collection
`W1 |NT71T
`V- 384, no. 1_2
`Jan. 15 2010
`
`15 JANUARY 2010
`'
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`[SSN 0373'5173
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`PHARMACEUTICS
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`NAN OTECHNOLOGY
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`VOL. 384,41—2 (2010)
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`

`

` International Journal of Pharmaceutics
`
`As.
`55$
`
`-J‘.'
`
`'
`
`
`[SEVIER
`
`International Journal of Pharmaceutics 384 (2010) 1—3
`
`
`Contents lists available at ScieneeDireet
`
`journal homepage: www.clsavier.comllocatelijpharm
`
`
`
`IaR
`
`eview
`
`Transungua] drug delivery: Current status
`
`Rania Elkeebashl, Ali AliKhan bv‘. Laila Elkeeb 5‘. Xiaoying Hui“, Howard 1. Maibacha
`a Department ofDermatology. School ofMedicine. University ofColifamia. San Francisco, CA 94 l43-0989. USA
`b School of Medicine. University of California, Do M's. CA. USA
`‘ Department ofDennoiology. School ofMedicine. University of California. more. CA. USA
`
`ARTICLE INFO
`
`
`Article history:
`EEEE ignlgie 2:10;)
`22 September‘ggfle 0””
`Accepted 1 enabler 2mg
`Manama Dnl‘lneg October 2009
`
`
`ABSTRACT
`
`
`Topical therapy is highly desirable in treating nail disorders due to its localized effects. which results
`in minimal advctsc'sy'stemic events and possibly improved adherence. However. the effectiveness of
`topical therapies is limited by minimal drug permeability through the nail plate. Current research on nail
`permeation that focuses on altering the nail plate banner by means of chemical treatments. penetration
`enhancers as well as phystcal and mechanical methods is reviewed. A new method of nail sampling is
`examined. Finally [imitations ofcurrent ungual drug permeability studies are briefly discussed.
`(Q 2009 ElSEViEf BN. All rights reserved,
`
`Keywords:
`Ungual drugdelivery
`Onycl'lomycosis
`Nail penetration
`Antifungal
`Dnycl'iopharmacokinetics
`
`
`Contents
`
`5.2.
`
`Introduction ........................................................................................................................................ ..
`1.
`Topical drug delivery to the nail and available formulations .. .
`..
`2.
`
`3. Human nail ............................ ..
`. . ..
`4.
`Nail sampling . . . .
`. . .
`.
`.
`.
`.
`.
`.
`. . .
`. .
`.
`. .
`.
`
`5.
`Enhancing nail penetration ....... ..
`5.1. Mechanical methods to enhance nail penetration. .... ...................... ..
`
`5.1.1.
`Nail abrasion .......................... ..
`
`5.1.2.
`Nail avulsion .......................... ..
`
`Chemical methods to enhance nail penetration .............. . .
`5.2.1. N-acetyl-L-cysteine and mercaptan compounds .... ..
`
`.
`.
`.
`.
`..
`5.2.2.
`2—n—nony1—1.3—dloxolane .......................... . .
`
`Keratolytic enhancers ............................................................................................................ ..
`5.2.3.
`5.2.4.
`Keratinolytic enzymes ............................................................................................................ ..
`Physical methods to enhance nail penetration
`5.3.1.
`Iontophoresis . . . .
`.
`.
`.
`.
`. . . . . . . . . . . . . . . ..
`
`. . .
`. ..
`5.3.2.
`Etching . . . . . .
`. . .
`. . .
`. _ .
`. .
`. .
`.
`. .
`5.3.3.
`Carbon dioxide laser . .
`.
`. ..
`
`5.3.4. Hydration and occlusion .................. ..
`..
`
`New frontiers in physical penetration enhancement ...................................................................................... ..
`
`Lasers ................................................................. ..
`5.4.1.
`
`Phonophoresis ........................................................................... .
`.
`5.4.2.
`
`5.4.3. Ultraviolet light ............................................................................ . .
`. ..
`Photodynamic therapy ofonychornycosis with aminolevulinic acid ............................................................ . .
`5.4.4.
`
`5.3.
`
`5.4.
`
`2
`2
`2
`2
`3
`3
`3
`3
`3
`3
`3
`4
`4
`4
`4
`5
`5
`5
`6
`6
`5
`[5
`6
`
`“ Corresponding author at: CID Dr. tl.l. Maibach. Department ofDeri-natology. School of Medicine. UCSF. 90 Medical Center Way. San Francisco. CA 51414-0989,
`USA. Tel.: il M5 476 49971738 8523: fax: +1 415 753 5304.
`E-rnoil addresses: i'elkeeb@yalioo.com (R. Elkeeb). Maibacl11l®detmucsfiedu (H1. Maibacli).
`1 Rania Eliteeb. Ali Nikhan and laila Elkeeb have contributed equally to the work.
`
`0378—5173}! - see front matter © 2009 Elsevier B.V. All rights reserved.
`doiIIOJ 01Gi'j.ijpharm.2009.lf}.002
`
`Page 5 of 13
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`

`

`R. Elkceb et at. / lntcmationaljoumal ofPhonnoceutirs 384 (2010) 1—8
`
`Formulations may improve penetration ............................... ..
`5'
`
`7, New drugs .................................. . ._ .
`.
`.
`.
`.
`.
`............... ..
`3_
`Limitations otcurrent ungual drug permeability studies ............. __
`8 1. Use ofanimal hooves as a model for nail penetratiaan ________
`
`82,
`use or nail clippings as a model of nail penetration ____ ,,
`8.3.
`Super hydration method ........... .
`.I.......................... __
`8.4.
`Correlation ofin vitro to in vivo studies ....................... ..
`References ............................................................. ..
`
`
`
`
`
` ‘del-JGIGIGGT
`
`______ _.
`
`
`
`
`I. Introduction
`
`The importance of nail permeability to topical therapeutics
`has been realized. primarily in the treatment of onydiomycosis,
`which affects approximately 19% of the population {Gupta and
`Scher. 1998). Topical therapy is highly desirable due to its localized
`effects. which results in minimal adverse systemic events and pos-
`sibly improved adherence. Recent advances in topical transungual
`delivery have led to the development ofantifungal nail lacquers,
`However, the effectiveness of topical therapies is limited by mini-
`mal drug permeability through the nail plate (Baron and Kaoukhov.
`2005). Current research on nail permeation focuses on altering the
`nail plate barrierby means ofchemical treatments (Kobayash i et al..
`1998; Malhotra and Zatz, 2002) and penetration enhancers (Hui et
`al.. 2003). Physical and mechanical methods are also under exami—
`nation.
`
`2. Topical drug delivery to the nail and available
`formulations
`
`Mycotic nail infections infrequently resolve spontaneously. and
`may have a substantial impact on quality oflife. Current treatment
`modalities include surgery. as well as oral and topical antifun-
`gal agents. However, a meta-analysis of randomized trials found
`little high quality evidence that any topical therapy is effective
`(Crawford and Hollis. 200?). Topical therapy is indicated when the
`nail matrix is not involved [in ~74% of patients) [Effendy et .31.,
`2005). it is preferred in elderly patients or patients receiving mul-
`tiple medications. in order to minimize drug-drug interactions.
`Topical therapy is also preferred in patients with mild-to—moderate
`disease and for those unwilling to use systemic medications.
`Topical therapy minimizes adverse systemic drug reactions, like
`those associated with oral antifungal agents (Elewski and Hay,
`1996).
`Multiple classes of antifungal medications have been utilized;
`these include: polyenes (cg. nystatin) which have both fungistatic
`and fungicidal properties in vitro: imiclazoles (eg. clotrilnazole, tio—
`conazole, econazole, ketoconazole, miconazole. sulconazole. and
`oxiconazole). which have fungistatic properties in vitro; and ally-
`lamineslbenzylamines [e.g. naftifine, terbinafine, and butenafine),
`which have fungistatic and fungicidal properties in vitro (Turn and
`l(ane.1999),
`Only one topical therapy has been FDA approved for onycltomy—
`cosis: ciclopirox nail lacquer 8% solution. Ciclopirox inhibits the
`transport ofessential elements into the fungal cell, thus disrupting
`DNA. RNA. and protein synthesis. It is a broad—spectrum antifungal
`with activity against dermatophytes and some non-derma tophyte
`molds.
`Two randomized, controlled trials suggest that complete reso] u-
`tion occurs in approximately 7% oftreatcd patients compared with
`0.4% using placebo.Thus. onlyl oflfi patients usingthe lacquerwill
`have a favorable outcome which involved reaching a clinically and
`mycologically cured target nail (treatment cure). Treatment curc-
`comprised ofa negative cultu re and negative potassium hydroxide
`(KOH) as well as global evaluation score=cleared (100% clearance
`
`of clinical signs of disease): furthermore, recurrence is common
`after discontinuing therapy [Gupta et 3].. 2600).
`in Europe. amorolfine and ciclopirox (nail lacquer 8% solution)
`have been approved for onychomycosis treatment. Amorolfine,
`available as a nail lacquer. acts by inhibiting the biosynthesis of
`ergosterol, a component of the fungal cell membranes. Amorolfine
`is fungistatic and fungicidal and most effective against dermato-
`phytes, but can be used for yeast and molds with lesser efficacy
`(Haria and Bryson.1995).
`The clinical efficacy of amorolfinc therapy in 727 patients with
`toenail or fingernail onychomycosis was evaluated. A mycological
`and clinical cure was achieved in 45—50% of the patients treated
`with 5% amorolfine lacquer once or twice weekly for 5 months at 3
`months post—treatment (Zaug and Bergstraesser. 1992).
`
`3. Human nail
`
`The chemical composition of the human nail differs signifi-
`cantly from other body membranes. The plate. composed of keratin
`molecules with many disulphide linkages and low associated lipid
`levels, does not resemble any other body membrane in its bar-
`rier properties — it behaves more like a hydrogel than a lipophilic
`membrane.
`Drug transport into the nail plate is influenced by: physico-
`chemical properties of a drug molecule (size, shape, charge. and
`hyd rophobiciiyl. formulation characteristics ( nature of the vehicle
`and drug concentration), presence of permeation enhancers. nail
`properties (thickness and hydration). and interactions between the
`permeant and the keratin network of the nail plate. The chem-
`ical composition and some experimental evidence indicate that
`the aqueous pathway plays the dominant role in drug penetration
`through the nail. Furthermore, wateris the principle nail plasticizer.
`Once hydrated, the nail becomes more elastic and possibly more
`permeable to topically applied substances. However. the effects
`of hydration on nail permeation requires elucidation (Cunt and
`Kasting, 2006).
`
`4. Nail sampling
`
`Permeation studies with modified in vitro diffusion cells com-
`monly utilized for flux determination. Drug is initially applied to
`the nail dorsal surface. Permeation is measured by sampling the
`solution on the ventral nail plate at successive time points. and cal-
`culating drug flux through the nail. This method bears Similarities
`to skin penetration studies. However, skin penetration studies are
`not limited simply to determination of flux. but also include the
`separation of skin layers to quantify drug concentration in each
`layer.
`A novel technique developed by Hui ct al. enables the determie
`nation ofclrug concentration within the plate. where fungi reside.
`This method relies on a drilling System which samples the nail core
`without disturbing its surface (Fig. 1). This is achieved by the use
`ofa micrometer—precision nail sampling instrument that enables
`finely controlled drilling into the nail with collection ofthe powder
`created by the drilling process. Drilling of the nail occurs through
`
`Page 6 of 13
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`it. Elket'b et (ll. f internationalJournal of Pharmaceutics 384 (2010) [—8
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`3
`
`
`
`Fig. i. The sampling device.
`
`the ventral surface. The dorsal surface and ventrally—accessed nail
`core can be assayed separately. The dorsal surface sample con-
`tains residual drug. while the core from the ventral side provides
`drug measurement at the site ofdisease. This method permits drug
`measurement in the intermediate nail plate. which was previously
`impossible [Bronaugh and Maibach. 2005].
`
`S.l.l. Naif abrasion
`Simply stated. nail abrasion involves sanding of the nail plate
`to reduce thickness or destroy it completely. Sandpaper number
`150 or 180 can be utilized. depending on required intensity. Sand-
`ing must be done on nail edges and should not cause discomfort
`[Di Chiacchio et al.. 2003}. An efficient instrument for this proce—
`dure is a high—speed (350.000 rpm) sanding hand piece (Baran et al..
`2003). Additionally. dentist's drills have been used to make small
`holes in the nail plate. enhancing topical medication penetration
`(Di Chiacchio et al., 2003).
`Nail abrasion thins the nail plate. decreasing the fungal mass of
`onychomycosis. and exposing the infected nail bed. in doing so. it
`may enhance the action of antifungal nail lacquer. The procedure
`may be repeated for optimal efficacy {Ben}. 1973}.
`
`A
`I
`A
`5.1.2. Nailavtdsion
`Total nail avulsion and partial nail avulsron involve surgical
`removal of the entire nail plate or partial removal of the affected
`nail plate. and under local anesthesia.
`Keratolytic agents such as urea and salicylic acid soften the nail
`plate for avulsion. Urea or a combination of urea and salicylic acid
`have been used for nonsurgical avulsion (chemical avulsion} in clin-
`ical studies. prior to topical treatment ofonychomycosis (Hettinger
`and Valinsky. 1991]. Nail abrasion. using sandpaper nail files. prior
`to antifungal nail lacquer treatment may decrease the critical fungal
`mass and aid penetration (Di Chiacchio et al., 2003).
`
`5. Enhancing nail penetration
`
`5.2. Chemical methods to enhance nail penetration
`
`Physical. chemical and mechanical methods have been used
`to decrease the nail barrier. Within each of these broad cate—
`gories. many techniques exist to enhance penetration. Mechanical
`modes of penetration enhancement are typically straightforward.
`and have the most in vivo experience associated with them. in co n—
`trast. many of the chemical and physical methods discussed are
`still in the in vitro stages ofdevelopment: laboratory studies are
`currently examining these techniques using human nail samples.
`The goal of topical therapy for onychomycosis is drug pene-
`tration into deep nail stratums at amounts above the minimal
`inhibitory concentration (MIC). Effective penetration remains chal-
`lenging as the nail
`is believed by some to be composed of
`approximately 25 layers oi'tightly bound keratinized cells. TOO-fold
`thickerthan the stratum corneum [5C)(Hao and Li. 2008b}. Fu rther—
`more. De Berker et al. have observed increase in toe nail thickness
`along the nail. Mean nail plate thickness increased progressively
`along the entire length of the nail ranging between 590 pm and
`1080 pm (De Berkcr et al.. 1996). While there is disagreement on
`the exact thickness ofthe nail there is consensus that the nail strucw
`ture is difficult to penetrate. In addition. poor permeability and
`prolonged transport lag time contribute to disappointing topical
`efficacy in nail diseases [Hao and Li. 2008b}.
`Chemical and physical modes ofpenetration enhancement may
`improve topical efficacy. There are two main factors to consider;
`physicochemical properties ofthe druglpolar compounds are more
`permeable) and binding ofthe drug to keratin within the nail. Bindr
`ing to keratin reduces availability ofthe active (free) drug, weakens
`the concentration gradient. and limits deep penetration (Murthy et
`al., 2007b).
`
`Studies examining the efficacy of chemical compounds with
`transungua] penetration properties are currently underway. As
`would be expected. skin penetration enhancers do not usually have
`the same effect on nails (Walters et al., l985}. Thus far. only a few
`chemicals which enhance drug penetration into the nail plate have
`been described.
`
`I
`5.2.1. N—aceryl-i.-cysteine and mercoptan compounds
`Kobayashi et al. demonstrated that N—acetylnL-cysteine and 2—
`mercaptoethanol.
`in combination. enhanced permeability of the
`antifungal drugtolnaftate into nail samples(l<obayasln et al., 1998:),
`They suggested that these compOunds may be generally useful in
`enhancing drug permeation across the nail plate.
`I
`Hoogdalem et al. evaluated the penetrahon-enhancmg proper—
`ties ofN—acetyl-L—cysteine with the antifungal drug oxiconazole in
`vivo. N-acetyl-t—cysteine promoted oxiconazole l'EtEfltIUn [[1 upper
`nail layers (Hoogdalem et 3.1.. 1997].
`I
`‘
`Malhotra and Zatz screened nail penetration enhancers. includ-
`ing: mercaptan compounds. sulfites. bisulfites. keratolytic agents
`and surfactants in vitro. N12-n1ercaptopropionyl)glycine, demon—
`strated superior penetration enhancement to all other compounds,
`urea acted synergistically to increase nail permeation to the great—
`est extent (Mallmti-a and Zatz. 2002). However. postal-earment
`barrier integrity studies demonstrated that changes induced in
`the nail keratin matrix by these effective chemical modifiers were
`irreversible. It is believed that these enhancers act by breaking
`disulphide bondS. which are responsible for nail integrity thus pro.
`ducing structural changes in the nail plate (Malhotra and Zarz.
`2002: Murdan, 2007).
`
`5.]. Mechanical methods to enhance nail penetration
`
`Mechanical methods including nail abrasion and nail avulsion.
`have been used by dermatologists and podiatrists for many years -
`with varying results. Additionally. they are invasive and potentially
`painful. Thus. current research focuses on less invasive chemical
`and physical modes of nail penetration enhancement.
`
`5.2.2. 2-n—nonyi-1,3—(iioxoiune
`Hui et a]. have showed that 2—n—nonylwl.3adioxolane (SEPA‘E’)
`enhances penetration of econazole [from a lacquer formulation)
`into the human nail (Hui et al., 2003). They demonstrated that
`econazole penetrates the nail six times more effectively in a lacquer
`containing 2—n—nonyl—i.3—dioxolane titan in an identical lacquer
`without enhancer. Concentrations of econazoie in the deep nan
`
`Page 7 of 13
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`4 l
`
`ayer and nail bed were significa ntly higher in the 'enhancer‘ group
`than in the control group. Furthermore. in the ‘enhancer' group,
`econazole concentration in the deep nail layer was 14.000 times
`greater than the MIC necessary to inhibit fungal growth.
`
`R. Elkeeb er al. / loternationoljoumol ofPhonnaceutics 384 (20w) l—s
`
`lontophoresis
`5.3.1.
`lontophoresis involves delivery of a compound across a mem-
`brane using an electric field (electromotive force). The principle
`has been applied clinically for cutaneous anesthesia. hyperhidrosis
`management, antibiotic penetration. and herpes simplex treat-
`ment (Kassan et al.. 1996). Currently both LidoSite® [lidocaine
`HCllepinephrine topical iontophoretic patch) and GlucoWatch®
`(iontophoretic measurement of glucose in diabetics) are FDA
`approved. lontophoresis has been used for various applications
`different from transdcrmal ophthalmic. dental. orthopaedic. etc.
`(Homath-Winter et al.. 2005: Nowiclci et al.. 2002: Chen et al_,
`2008). Drug diffusion through the hydrated keratin ofa nail may
`be enhanced by iontophoresis.
`Several factors contribute to this enhancement: electrorepul—
`sionlelectrophoresis. interaction betwaen the electric field and
`the charge of the ionic permeant: electroosmosis. convective sol-
`vent flow in preexisting and newly created charged pathways;
`and permeabilizationlelectroporation, electric field-induced pore
`induction [Murthy et al.. 2007b; Han and Li. 2008b).While transport
`enhancement ofneutral permeants relies on electroosmosis, trans:
`port enhancement of ionic permeants relies on electrophoresis and
`electroosmosis.The effects ofelectric current on nails are reversible
`in vitro; nail plates will return to normal after iontophoresis treat~
`merit (I lao and Li, 2008b).
`Murthy et al. elegantly examined transport of salicylic acid
`(SA) across the human nail plate (Murthy et al.. 2007b).
`In
`vitro transport studies were performed using specifically-designed
`diffusion cells. Compared to passive transport. iontophoresis signifk
`icantly enhanced drug penetration through the nail. lontophoretic
`trans—nail flux improved with higher SA concentrations (up to
`2 mglml]. higher current density (up to 0.5 mAlcmz). higher buffer
`ionic strength [optimal strength at 50—100mm]. and higher pH.
`Murthy reported increased transungal glucose and griseofulvin
`flux with higher pH (pH>5) in anodal iontophoresis {Murthy et
`al., 2007a). pH dependent transport due to cathodal iontophore—
`sis followed the opposite trend (Le. lower pH correlated with
`increased flux). Griseofulvin transpart was enhanced mS-fold with
`iontophoresis.
`Hao and Li performed in vitro iontophoresis experiments
`on human nails with neutral and charged molecules. Anodal
`iontophoresis at 0.3 mA enhanced mannitol
`(MA) and urea
`(UR) transport compared to passive diffusion. Additionally, find—
`ings suggested only marginal contribution of electroosmosis in
`anodal iontophoretic transport of MA and UR using low elec-
`tric current (50.3 mt). Electroosmosis contribution increased with
`permeant molecular size and current strength (Han and Li.
`2008b].
`This group examined the effects of pH and ionic strength on
`clectroosmotic transungual transport of neutral compounds (Han
`and Li. 2008a). When pH was below the isoelectric point (pi)
`(pH<5}, the nail plates were positively charged. and clectroos-
`motic flow occurred from cathode to anode. Conversely, when pH
`was above pl (pH > 5]. the nail plates were negatively charged. and
`electroosmotic flow occurred from anode to cathode. Furthermore.
`clectroosmosis improved significantly from pH 7.4 to 9 in anodal
`iontophoretic transport. As discussed previously. electroosmosis
`contribution was greater in MA than UR due to increasad molecu-
`lar size. Additionally