JOURNAL OF
`
`harmacy and
`harmamlogy
`
`
`
`NUMBER 3
`
`MARCH 1997
`
`ISSN 0022-3573
`
`PHARM A53Y Ll§3;Bi-MY
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`6°!|]5E'E.B[:.Bl3
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`mummmwumlumur
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`i
`1
`
`Journal of Pharmacy and Pharmacology
`
`Published by The Royal Pharmaceutical Society of Great Britain
`1 Lambcth High Street, London SE1 7JN Telephone 0171-735 914]
`Telegrams Pharmakon London SE1
`E-Mail JPP@dial.pipex.con1
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`EDITOR
`
`Dr J. CHAMBERLAIN
`
`ASSISTANT EDITOR
`
`Dr A. L. SUGDEN
`
`EDITORIAL ASSISTANT
`
`G. M. MCMAHON
`
`EDITORIAL BOARD
`
`BoardMembers
`ProfessorB. W. BARRY,UniversityofBradford
`
`Professor E. BEUBLER, University of Graz, Austria
`Professor N. G. BOWERY, University of Birmingham
`Professor D. D. BREIMER, University of Leiden, The Netherlands
`Dr K. J. BROADLEY, Welsh School of Pharmacy, Cardiff
`Dr D. A. COWAN, Kings College, London
`Professor S. P. DENYER, University of Brighton
`Professor F. J. EVANS, School of Pharmacy, London
`Professor A. T. FLORENCE, School of Pharmacy, London
`Professor J. L. FORD, Liverpool John Moores University, Liverpool
`Professor D. GANDERTON OBE (Chairman), British Pharmacopoeia, London
`Professor P. G. JENNER, King’s College, London
`Professor T. M. JONES, Association of British Phannaceutical Industry, London
`Professor I. W. KELLAWAY, Welsh School of Pharmacy, Cardiff
`Dr W E. LINDUP, University of Liverpool
`Professor R. J. NAYLOR, University of Bradford
`Professor K. D. RAINSFORD, Sheffield Hallam University, Sheffield
`Professor B. TESTA, University of Lausarme, Switzerland
`Dr E. TOMLINSON, GeneMedicine Inc, Texas, USA
`Professor G. T. TUCKER, Hallamshire Hospital, Sheffield
`Dr B. WIDDOP, Poisons Unit, New Cross Hospital, London
`
`Secretary to the Board
`J. FERGUSON OBE
`
`COPYRIGHT © 1997 Journal ofPharmacy and Pharmacology.
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`

`
`Contents
`
`VOLUME 49 0 NUMBER 3 0 MARCH 1997
`
`Research Papers
`Pharmaceutics
`G ERTAN E KARASULU D DEMIRTAS M ARICI
`T GUNERI
`
`Release characteristics of implantable cylindrical
`polyethylene matrices
`
`Biopharmaceutics
`R P SHREWSBURY L W JOHNSON s R OLIVER
`Influence of moderate haemodilution with
`Fluosol or normal saline on carbaryl disposition
`in Sprague-Dawley rats
`D MERTIN B C LIPPOLD
`In-vitro permeability of the human nail and of a
`keratin membrane from bovine hooves:
`penetration of chloramphenicol from lipophilic
`vehicles and a nail lacquer
`
`241-245
`
`246-252
`
`Medicinal Chemistry
`V PEREZ—ALVAREZ M S MORALES-RIOS E HONG
`P JOSEPH-NAT]-IAN
`
`253-256
`
`257-262
`
`Synthesis of 3-amino-2-(3-indolyl)propanol and
`propanoate derivatives and preliminary
`cardiovascular evaluation in rats
`
`Drug Metabolism
`S KITAMURA K SUGIHARA M KUWASAKO
`K TATSUMI
`The role of mammalian intestinal bacteria in the
`reductive metabolism of zonisamide
`A NOMURA E SAKURAI N HIKICH.I
`Stereoselective N-demethylation of
`chlorpheniramine by rat-liver rnicrosomes and
`the involvement of cytochrome P450 isozymes
`M J THOMASON W RHYS—W]LLIAMS A W LLOYD
`G W HANLON
`Optimization of the chiral inversion of 2-
`phenylpropionic acid by Vérticillium lecanii
`P MEISEL S LANGNERW SIEGMUND
`In-vitro binding of propiverine hydrochloride and
`some of its metabolites to serum albumin in man
`M A C BENEDITO
`Fluorimetric determination of tissue distribution
`and diiferences between the activity of aspirin
`esterases I and II in mice and rats
`
`Pharmacokinetics
`M I BAZIN-REDUREAU C B RENARD
`J-M G SCI-[ERRMANN
`
`288-292
`
`293-295
`
`S PA BOOM S HOET F G M RUSSEL
`Saturable urinary excretion kinetics of famotidine
`in the dog
`M GANTENBEIN L ATTOLINI B BRUGUEROLLE
`Kinetics of bupivacaine after levcromakalim
`treatment in mice
`
`296-300
`
`Toxicology
`B M KARLSSON L M WAARA S-A FREDRIKSSON
`L~O D KOSKINEN
`
`The effect of the calcium antagonist nimodipine
`on the detoxification of soman in anaesthetized
`rabbits
`
`301-304
`
`Pharmacology
`M O M TANIRA B H ALI A K BASHIR F F EL—SABBAN
`M AL HOMSI
`
`Neuromuscular and microvascular changes
`associated with chronic administration of an
`extract of Teucrium stoc/csianum in mice
`G ECKER P CHIBA K-J SCHAPER
`
`305-309
`
`310-314
`
`315-318
`
`Estimation of the chemosensitizing activity of
`modulators of multi-drug resistance via
`combined simultaneous analysis of sigmoidal
`dose-response curves
`T ARAKI H KATO K SHUTO Y ITOYAMA
`
`Age-related changes in [3H]nimodipine and
`[3H]rolipram binding in the rat brain
`ZGGAOWYCUIBYLIUCGLIULWANG
`Anticholinergic activity and receptor-binding
`properties of a series of synthetic tropane
`derivatives
`
`319-321
`
`S GIACOMELLI L BRAGHIROLI A PONZIANELLI
`D W KOPPENAAL G DE FEO
`
`322-328
`
`329-331
`
`A sensitive assay for studying dopaminergic
`activity in cultures of rat pituitary cells
`SFSAADMTKHAYYALASATTIAESFSAAD
`Influence of certain calcium-channel blockers on
`some aspects of lorazepam-dependence in mice
`Natural Products
`C AHUMADAT SAENZ D GARCIA R DE LA PUERTA
`A FERNANDEZ E MARTINEZ
`The eifects of a triterpene fraction isolated from
`Crataegus monogyna Jacq. on different acute
`inflammation models in rats and mice. Leucocyte
`migration and phospholipase A2 inhibition
`
`332-335
`
`Analytical Biochemistry
`J SIAN D T DEXTER G COHEN P G JENNER
`C D MARSDEN
`
`Pharmacokinetics of heterologous and
`homologous immunoglobulin G, F(ab’)2 and Fab
`afier intravenous administration in the rat
`
`336-344
`
`M T MARINO M R URQUHART M L SPERRY J VON
`BREDOW L D BROWN E LIN T G BREWER
`Pharmacokinetics and kinetic—dynamic
`modelling of aminophenones as methaemoglobin
`formers
`
`Comparison of HPLC and enzymatic recycling
`assays for the measurement of oxidized
`glutathione in rat brain
`S C CONNOR M G HUGHES G MOORE C A LISTER
`S A SMITH
`
`Antidiabetic efficacy of BRL 49653, a potent
`orally active insulin sensitizing agent, assessed in
`the C57BL/KsJ db/db diabetic mouse by non-
`invasive ‘H NMR studies of urine
`
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`
`This material may be protected by Copyright law (Title 17 U.S. Code)
`
`I pharm. Pharmacol. 1997, 49: 241-245
`Received July 9, l996
`Accepted November 5, 1996
`
`© 1997 J. Pharm. Pharmacol.
`
`In-vitro Permeability of the Human Nail and of a Keratin
`Membrane from Bovine Hooves: Penetration of Chloramphenicol
`from Lipophilic Vehicles and a Nail Lacquer
`
`DIRK MERTIN AND BERNHARD C. LIPPOLD
`
`Department of Pharmaceutical Technology, Heinrich-HeineUniversity, Universitdtsstrasse 1, D-40225
`Dzisseldotf Germany
`
`Abstract
`
`Lipophilic vehicles and especially nail lacquers are more appropriate for topical application on the nail than
`aqueous systems because of their better adhesion. This work has, therefore, studied the penetration through the
`human nail plate of the model compound chlorarnphenicol from the lipophilic vehicles medium chain
`triglycerides and n—octanol and from a lacquer based on quaternary poly(methyl methacrylates) (Eudragit
`RL). The results were compared with data obtained with a keratin membrane from bovine hooves.
`If the swelling of the nail plate or the hoof membrane is not altered by use of lipophilic vehicles, the
`maximum flux of the drug is independent of its solubility in the vehicle and is the same as that from a saturated
`aqueous solution. These vehicles are not able to enter the hydrophilic keratin membrane because of their non-
`polar character and so cannot change the solubility of the penetrating substance in the barrier. If the
`concentration of the drug in the nail lacquer is sufficiently high, the maximum flux through both barriers
`equals that from aqueous vehicles or even exceeds it because of the formation of a supersaturated system.
`Penetration through the nail plate follows first order kinetics after a lag-time of 400 h. The course of penetration
`through the hoof membrane is initially membrane-controlled and later becomes a matrix-controlled process
`because of the membrane’s greater permeability. Chlorarnphenicol
`is dissolved in the lacquer up to a
`concentration of 31%. The relative release rates from these solution matrices are independent of the drug
`concentration but they decrease on changing to a suspension matrix.
`These results show that drug flux is independent of the character of the vehicle and that penetration of the
`drug is initially membrane-controlled and changes to being matrix-controlled as the drug content of the lacquer
`decreases.
`
`The nail plate and the bovine hoof membrane behave like
`hydrophilic gel membranes rather than lipophilic partition
`membranes (Mertin & Lippold 1997). The maximum flux of a
`drug through both barriers is primarily a function of its water-
`solubility. Because aqueous solutions are not important in the
`topical
`therapy of nail
`infections, due to their insufficient
`adhesion, lipophilic vehicles or nail lacquers were investigated
`to determine whether the flux from these reached the max-
`
`imum obtained from aqueous vehicles.
`Studies of the penetration of the antifungal agents ciclopirox
`(Héinel & Ritter 1990; Nolting & Seebacher 1993) and amor-
`olfine (Polak & Zaug 1990; Franz 1992; Polak 1992) show that
`active drug concentrations are obtained in the whole nail plate
`after a few days. Little is, however, known about the rela-
`lionship between flux and concentration in the lacquer. The
`Influence of the release on the kinetics of nail penetration have,
`moreover, not yet been described.
`According to Fick’s law (eqn 1) the penetration rate from an
`aqueous solution at sink conditions is directly proportional to
`‘ht? drug concentration in the barrier on the donor side (CED)
`(Mertin & Lippold 1997):
`
`dM/dt : DBACBD/hB
`
`(1)
`
`in Which dM/dt is the amount penetrating per unit time, DB the
`
`T C°1T8Spondence: B. C. Lippold, Department of Pharmaceutical
`4§°““°10gy, Heinrich-Heine-University, Universitatsstrasse
`1, D-
`225 Dusseldorf, Germany.
`
`effective diffusion coefficient in the barrier, A the diffusion
`area, and hB the thickness of the barrier. For a suspended
`substance in a given vehicle,
`the saturation concentration
`(CSBD) forms on the donor side owing to partition. Then the
`maximum concentration gradient causes the maximum flux:
`
`Jmax = dMmax/dtA = DBCsBD/hB
`
`As long as the vehicle does not change the barrier (e.g. by
`deswelling),
`the maximum flux from a suspension is inde-
`pendent of the vehicle (Lippold 1984). The swelling of
`hydrophilic gel membranes should be unchanged in contact
`with lipophilic vehicles as long as they also stay in Contact
`with an aqueous solution. Simulating the swelling of a living
`nail, which is ventrally supplied by the richly vasculated nail
`bed, by using an aqueous solution as acceptor and a lipophilic
`vehicle as donor, the flux from a saturated solution should
`equal the maximum flux from an aqueous suspension assuming
`an identical extent of swelling.
`the model compound chlor-
`To test
`this hypothesis,
`amphenicol was used because it is relatively highly soluble in
`water, which causes sufficiently high fluxes, and it is analyti-
`cally easy to determine, through both the nail plate and the
`hoof membrane. Its molecular size is, moreover, in the range of
`most antimycotics and the results can, therefore, be transferred
`to these drugs. Differences between the solubilities of chlor-
`amphenicol in pH 7-4 phosphate buffer on the one hand and
`in medium-chain triglycerides and n—octanol on the other
`
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`
`242
`
`DIRK MERTIN AND BERNHARD C. LIPPOLD
`
`Solubility of chloramphenicol in pH 7-4 phosphate buffer,
`Table l.
`n-octanol and medium-chain triglycerides at 32°C.
`
`Vehicle
`
`Phosphate buffer, pH 7-4
`n-Octanol
`Medium-chain triglycerides
`
`N = 3, mean :l: s.d.
`
`Solubility (mg L“)
`
`4520j:64
`23210 :l: 767
`2350 :l: 13
`
`(Table 1) seem to be large enough to indicate a possible
`influence of drug solubility in the Vehicle on the maximum flux
`through the barrier.
`Results obtained using lipophilic liquids should be trans-
`ferable to nail lacquers, assuming that membrane diffusion,
`and not release from the polymer, is the rate-limiting step. For
`both barriers, however,
`it must be investigated whether the
`penetration rate is controlled by the permeability of the barrier
`as well as the release of drug from the lacquer. The liberation
`of a substance which is suspended or dissolved in a nail lacquer
`should follow kinetics typical of a matrix system. From Fick’s
`first law Higuchi (1961) developed an equation for the release
`of a suspended drug from a matrix (sink conditions):
`
`Q = Ax/(Dei=rCs(2Co ‘ Cs)t)
`
`(3)
`
`Where Q is the amount of drug released at time t, A is the
`release area, Deg is the effective diffusion coefficient in the
`matrix, C5 is the solubility of the drug in the matrix, and Co is
`the initial concentration of the drug in the matrix.
`On the premise that CO >> C5 equation 3 can be reduced to:
`
`Q = A«/(2DefrCsCot)
`
`(4)
`
`Higuchi also deduced an equation describing the course of
`liberation of a drug which is completely dissolved in the matrix
`(up to 30% release, sink conditions):
`
`Q = ?-ACo~/(Derrt/TI)
`
`Transformation of this equation leads to:
`
`Q/Q0 = (2A/VL)«/(Dent/7?)
`
`(5)
`
`(5)
`
`in which Q0 is the initial amount of drug in the matrix and VL
`the matrix volume. Equation 6 shows that the relative release
`rate (Q/Q0) is, in contrast with equation 4, independent of the
`amount of drug incorporated and so enables distinction
`between solution and suspension matrix.
`The release rate can deviate from the ideal t/t kinetic,
`especially at the beginning of the process, if the drug has to
`penetrate an adherent membrane or aqueous layer after leaving
`the matrix. Roseman & Higuchi (1970) described the course
`of penetration from such systems by combining equations 1
`and 4.
`
`investigated the penetration of chlor-
`This work has
`amphenicol from lacquers based on quaternary poly(methyl
`methacrylates) with dibutyl sebacate as a plasticizer through
`the nail plate and the hoof membrane. Eudragit RL was used
`because of its ten-fold higher permeability in comparison with
`Eudragit RS (Lehmann 1989). Because previous results have
`shown the permeability characteristics of both barriers to be
`similar (Mertin & Lippold 1997), most of the investigation was
`performed with the hoof membrane.
`
`Studies with different drug concentrations in the polymer
`(from 2-2 to 47-6%) should show whether penetration from the
`lacquer is matrix- or membrane-controlled.
`
`Materials and Methods
`
`Chemicals
`
`A phosphate buffered saline solution, pH 7-4, was used as
`acceptor. Chloramphenicol was obtained from Caesar & Lor-
`entz (Hilden, Germany), medium-chain triglycerides (Miglyol
`812)
`from Hiils AG (Witten, Germany), n-octanol
`and
`methanol from J. T. Baker (Deventer, Netherlands), Eudragit
`RL PO from Réihm GmbH (Darmstadt, Germany) and dibutyl
`sebacate (Rilanit DBS) from Henkel KGaA (Diisseldorf, Ger.
`many). HPLC-grade methanol (chromasolv methanol) is 3
`product of Riedel-de-Haén (Seelze, Germany).
`
`Penetration studies
`
`The modified Franz diffusion cells, the preparation of the nails
`and the hoof membranes and the performance of the penetra-
`tion studies have been described in an earlier publication
`(Mertin & Lippold 1997). For experiments with lipophilic
`liquid vehicles, chloramphenicol was used in a suspended form
`with its maximum thermodynamic activity. The formation of a
`saturated solution was guaranteed by stirring at 32°C for 48 h.
`Despite occasional very long penetration times no visual
`degradation of the nails was observed.
`
`Analytical conditions
`The HPLC method differs from that described earlier (Mertin
`& Lippold 1997) in one aspect: the mobile phase acetonitri1e-
`water (3:1) was pumped at flow rates ranging from 1-0 to
`1.25 mL min‘ 1.
`
`Composition and application of the lacquer solution
`The effect of concentration was examined by varying the
`amount of chloramphenicol between 0-5 and 20% of the lac-
`quer solution-equivalent to between 2-2 and 47-6% of the dry
`lacquer. The formulations were: Eudragit RL PO, 200%?
`dibutyl sebacate, 2-0%; chloramphenicol, 0-5, 5-0, 10-0 and
`20-0%; and methanol to 100%.
`The swollen membrane was fixed in the empty diffusion C611
`and dried under ambient conditions for 2h. A 200—pII1 film
`resulted after application of the lacquer solution (500 pL on to
`about 2-5 cm2 hoof membrane and 120 pL on to 0-64 crnz nail
`plate), initial drying with warm air for a period of 30 min and
`final drying at room temperature for 24h. The filling Of the
`acceptor compartment started the experiment.
`
`Results and Discussion
`
`_
`Penetration from lipophilic liquids
`Phosphate buffer pH 7-4, n-octanol and medium-chain mgly‘
`cerides were used as donors (medium-chain triglycerides 0"”
`in experiments with hoof membrane). Table 2 shows
`imum fluxes (Jmax (1000 pm)) from the different Veh‘°1_eS’
`standardized to a barrier thickness of 1000 pm corr65P°ndmg
`to the average thickness of the big-toe nail.
`
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`
`PERMEABILITY OF NAIL AND KERATIN MEMBRANE
`
`Table 2. Maximum flux of chloramphenicol. standardized to a barrier thickness of 1000 um
`(Jmx(l0O0 pm», from different vehicles through hoof membrane and nail plate at 32°C.
`Vehicle
`
`Maximum flux of czhlorlamphenicol
`(mg cm’ s’ )
`
`Hoof membrane
`Nail plate
`4-0711.13 x 10-5
`Phosphate buffer, pH 7-4
`8»21:I:2-11 x 10-7
`n—Octanol
`3-40j:O~68 x 10"“
`9-13d:0-63 x 10-7
`4-06j:1-00 x 10*‘
`n.d.*
`Medium-chain triglycerides
`
`*Not determined. N :3 or 4, mean :1: s.d.
`
`01 O
`
`Fluxes through the hoof membrane are forty-fold those
`through the nail plate, confirming the different permeability of
`the barriers (Mertin & Lippold 1997). It is, however, more
`interesting that the vehicle has no influence on the maximum
`flux. There is no significant difference (P=0-05) between the
`fluxes from the various vehicles through both barriers. Because
`me fluxes from lipophilic vehicles are equal to those from
`aqueous saturated solutions, the assumption that the flux is
`independent of the character of the vehicle is completely
`confirmed. Obviously, a saturated solution and, therefore, the
`maximum concentration gradient forms on the donor side of
`the water-swollen membrane owing to distribution. Neither
`medium-chain triglycerides nor n-octanol have significant
`influence on keratin swelling or
`the solubility of chlor-
`amphenicol in the membrane. It is of practical significance that
`the therapeutically desired maximum flux is reached as soon as
`the drug is present at its maximum thermodynamic activity, i.e.
`the saturated state. Although low solubility can be used to save
`drugs, very low solubilities lead to emptying effects, i.e. the
`flux cannot be maintained over the whole period of application.
`This result is of great importance in respect of drug penetration
`from nail lacquers.
`
`Penetration from nail lacquers
`Kinetics of penetration. Figs 1 and 2 illustrate the concentra-
`tion-dependence of the diffusion of chloramphenicol from
`Eudragit RL lacquers through the hoof membrane. Plotting
`the amount penetrated against t gives linear relationships after
`alag-time of a few hours; this is typical of matrix control (Fig.
`1). As expected for a solution matrix, the rate of penetration of
`chloramphenicol increases with the concentration of the drug
`in the matrix between 2-2 and 18-5% and so the relative release
`rates (i.e. the amount penetrated relative to the total amount in
`the lacquer) remain constant. Increasing the concentration in
`the lacquer to 47-6% has no effect on the penetration rate,
`however, and so the relative rates decrease. This proves that,
`except for the lacquer containing 47-6% chloramphenicol, all
`_‘YStEIns are solution matrices as the relative release rates are
`mflfipendent of the amount of drug incorporated, in accordance
`wlth equation 6. Because the relative release rate decreases by
`half for the 47-6% lacquer, this, therefore, can be characterized
`as 3 Suspension matrix. Fig.
`1 does not enable distinction
`hetween matrix- and membrane-controlled processes. For
`membrane-controlled release from a solution matrix,
`first-
`order kinetics are expected. The plot of the amount of drug
`remaining in the lacquer (logarithmic scale) against time (Fig.
`
`«PO
`
`
`
`
`
`(J0
`
`Amountpenetrated(%) E38
`
`3
`
`4
`
`Timel/2(h1/2)
`
`FIG. 1. Percentage penetration of chloramphenicol from Eudragit RL
`lacquers containing different concentrations, CL, of drug through the
`hoof membrane at 32°C (n=4, mean:l:s.d.). Chloramphenicol con-
`centration: O 2.2%, I 18.5%, A 31.3%, 9 47.6%.
`
`10
`
`20
`
`30
`
`40
`
`50
`
`Time (h)
`
`FIG. 2. Penetration of chloramphenicol from Eudragit RL lacquers
`containing different concentrations, CL, of drug,
`through the hoof
`membrane at 32°C, plotted as the amount of drug remaining in the
`lacquer (Q, ~ Q; n =4, meand: s.d.). Chloramphenicol concentration:
`C 2.2%, I 18.5%, A 31.3%, 0 47.6%.
`
`that membrane
`
`2) shows, because all curves are flattening,
`control does not occur over the whole period.
`The ideal Jt kinetics follow after the expiry of the lag-time
`because of the initially predominant membrane control. Delayed
`drug release from silicone matrices through aqueous adherent
`layers results in similar penetration profiles (Haleblian et al
`1971; Roseman 1972).
`
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`
`DIRK MERTIN AND BERNHARD C. LIPPOLD
`
`Table 3.
`Release exponent, n, for the penetration kinetics of chloramphenicol from Eudragit RL lacquers
`through the hoof membrane at different drug concentrations.
`
`CL (%)
`
`Calculated according to equation 7*
`
`Calculated according to equation Sl
`
`Exponent (n)
`
`0-67 i 0-04
`0-73 :1: 0-05
`0-70 :1: 0-02
`0-64 :l: 0-03
`
`r1
`
`0-9990
`0-9917
`0-9995
`0-9995
`
`Exponent (n)
`
`0-56 :1: 0-03
`0502!: 0-05
`0-62 :1: 0-03
`0-65 i 0-04
`
`l-lag
`
`1-55 :l:0-27
`3-28 :l:0-19
`1-45 i0-28
`0-09i0-18
`
`O-9999
`0-9985
`0-9999
`0-9999
`
`*Q/Qo=kt". +Q/Q0=k(t — tlag)“. ‘Correlation coefficient of the regression line. N :4, mean :I: s.d.
`
`The course of the drug release from a dosage form can be
`expressed by a semi-empirical function (Peppas 1985):
`
`Q/Qo = kt"
`
`(7)
`
`Where Q/Q0 has the same meaning as in equations 3 and 6, k is
`the release-rate coefficient, and n is an exponent which
`describes the kinetics. If release is delayed, neglecting the lag-
`time can lead to incorrect conclusions about the penetration
`kinetics.
`In this circumstance equation 8 offers a better
`approach:
`
`Q/Q0 = k(t — tlag)n
`
`The release exponent (n) and the lag-time can be determined
`by a computer-aided, iterative method. Here the lag-time is
`established by a progressive shift of the experimental curve to
`the left parallel to the abscissa, beginning with data from 5h
`onwards, inserting in the logarithmic form of equation 7 and
`subsequent
`linear
`regression to obtain the best curve fit
`(Lindner 1994). Table 3 shows the liberation parameters
`determined directly with equation 7 and iteratively with
`equation 8.
`Neglecting the lag-phase normally leads to overestimation
`of the release exponent n and a worse fit of the calculated curve
`to the experimental data; this is reflected in a lower correlation
`coefficient. With the exception of the lacquer containing
`47-6% chloramphenicol, the lag-time ranges from 1-4 to 3-3h
`and agrees with the values determined graphically from Fig. 1.
`The iterative exponents (0-50 to 0-62, Table 3) are in the range
`expected for pure matrix release (n=0-5) and confirm the
`visual assessment of the profiles. The exponent of the 47-6%
`lacquer is significantly different from unity which is expected
`for completely membrane-controlled release from a saturated
`vehicle. These results, on the other hand, correspond with the
`assumption of initial membrane control changing to matrix
`control as the drug content of the lacquer decreases.
`
`Fluxes from nail lacquers compared with liquid vehicles
`The profile between the first and the sixth hours after the start
`of the experiment was evaluated to determine the fluxes
`through the hoof membrane. Here the penetration rate is
`highest and there is an approximately linear
`relationship
`between the amount penetrated and time. This behaviour, not
`typical of matrix control, corresponds to the initial membrane-
`control. The expected first order kinetics (only dissolved drug
`in the lacquer) results in a more or less linear course for an
`amount penetrated of 10% at the most (pseudo steady-state).
`
`For saturated solutions (real steady-state), zero order kinetics
`prevail, which causes a linear increase of the concentration in
`the acceptor. Not before a sufficiently large emptying zone of
`the drug has developed, causing also a decrease in con.
`centration in the membrane, does the process become matrix.
`controlled.
`
`As the maximum flux is, in addition to antifungal power, the
`most important parameter for predicting the therapeutic effi-
`cacy of antimycotics,
`the penetration of chloramphenicol
`through the nail in man was investigated with a single for-
`mulation (3l-3%). Fig. 3 shows the low penetration rate and
`large lag-time in comparison with the thinner hoof membrane.
`The lag-time (about 400h) is significantly longer than for
`penetration from an aqueous
`suspension (about 200 h).
`Because both fluxes do not differ from each other in the
`
`steady-state (Table 4), the distinction cannot be explained by
`the different diffusion coefficients. Possibly the initially dry
`nail plate is slowly hydrated under the occlusive lacquer after
`contact with the acceptor medium, whereupon the partition
`equilibrium between polymer and nail plate and, therefore, the
`formation of the maximum concentration gradient, is delayed.
`The flux was calculated from the steady-state values between
`t=670 and 940h. Because of the lower penetration rate it
`should stay constant over a longer period than for the hoof
`membrane, for which the emptying area in the matrix widens
`after a short time and then the course of diffusion corresponds
`to classical x/t-kinetics. Thus, the hoof membrane has to be
`
`20
`
`0'20
`
`0-15
`
`200
`
`400
`
`600
`
`Time (h)
`
`) and
`FIG. 3. Penetration of chloramphenicol (CL = 31.3%
`RL lacquer through the hoof membrane (thickness, dg. =104l‘md Q“
`the nail plate (dg =953 pm) at 32°C (n=4, mean:l:s.d.)- QH fmem.
`are, respectively, the amounts of drug penetrated through l1°°
`brane (O) and nail plate (C).
`
`CFAD V. Anacor, |PR2015-01776
`ANACOR EX. 2194 - 7/8
`
`CFAD v. Anacor, IPR2015-01776
`ANACOR EX. 2194 - 7/8
`
`

`
`PERMEABILITY OF NAIL AND KERATIN MEMBRANE
`
`245
`
`Flux of chloramphenicol through the hoof membrane and
`4_
`Table
`nail plate at 32°C from Eudragit RL lacquers containing different
`Egwenuations of drug, CL, and from a saturated solution in pH 7-4
`Phosphate buffer.
`
`mation in the
`$333; (1%)
`
`Maximum flux of chlora_mpllenicol
`(J(1000 um); mg cm 2 s
`1)
`
`Nail plate
`Hoof membrane
` _
`
`21
`185
`,
`
`n.d.*
`3-10:0-39 x 1o‘7
`8-02:1:l-31 x 10*‘
`4.34:1-27 x 10*:
`dd.
`7-26:l:1-75 x 10‘
`n.d.
`8-113:2-16 x 10-5
`t d solution in
`8-21 i2-11 x 10”’;
`5-32:t1-62 x 10‘°
`gfiggghfite buffer
` —— .
`
`-rNot determined. Results
`n_.=3_7, mean :1: s.d.
`
`are standardized to d3 = 1000 um.
`
`used with caution as a model for studying controlled-release
`systems for application on nails.
`The fluxes of chloramphenicol, standardized to a barrier
`thickness of 1000 pm are in the same range as the maximum
`fluxes from aqueous suspensions (Table 4). Firstly, it is sur-
`prising that the flux through the hoof membrane from the more
`highly concentrated lacquers (for the 47-6% lacquer it is even
`statistically significant, P =O«05) is greater than that from an
`aqueous suspension. This can only be explained by the
`assumption of the formation of a supersaturated solution in the
`barrier. For the 31-3% Eudragit RL lacquer the development of
`a thermodynamically unstable supersaturated solution could be
`proved by polarization microscopy. This state seems also to be
`formed on the donor side of the hoof membrane, because of the
`distribution equilibrium, and remains until crystallization starts
`or the concentration falls below the solubility as a result of the
`emptying of the matrix. As the flux from the 18-5% lacquer is
`not significantly lower than the maximum flux from water, it
`has to be assumed that the solubility of chloramphenicol in the
`poly(methyl methacrylate) lacquer is in the same range. These
`findings are confirmed by the results of the nail plate—the flux
`from the 18-5% lacquer equals the maximum flux from water.
`The lacquer presented, consisting of a highly permeable
`quaternary poly(methyl methacrylate)
`(Eudragit RL) and
`dibutyl sebacate as a plasticizer, is, therefore, a suitable dosage
`form for achieving high drug fluxes through the nail plate and
`the hoof membrane. By addition of a sufficiently high con-
`centration of drug it is possible to achieve penetration rates
`Which correspond to those from saturated liquid vehicles
`
`(water or non-aqueous solvents) or even exceed those owing to
`the temporary formation of a supersaturated system. Because
`of the low permeability of the nail plate the release rate of the
`lacquer is not important in this instance. The rapid develop-
`ment of the partition equilibrium between lacquer and barrier
`is, however,
`significant and so high-swelling polymers
`(Eudragit RL) have to be preferred. It must, however, be
`considered that the dried lacquer remains water-insoluble when
`it becomes more hydrophilic-otherwise it would be removed
`by washing and, therefore, the application intervals have to be
`shortened. On the other hand, the occlusivity of the nail lac-
`quer is of some importance;
`this is probably increased for
`poorly swelling polymers with low water-vapour permeability.
`
`References
`
`Franz, T. J. (1992) Absorption of amorolfine through human nail.
`Dermatology 184 (Suppl. 1): 18-20
`I-Ialeblian, J., Runkel, R., Miiller, N., Christopherson, J., Ng, K. (1971)
`Steroid release from silicone elastomer containing excess drug in
`suspension. J. Pharm. Sci. 60: 541-545
`(ed.)
`In: Ryley, J. F.
`Héinel, H., Ritter, W.
`(1990) Formulation.
`Chemotherapy of Fungal Diseases (Handbook of Experimental
`Pharmacology, Vol. 96). Springer, Berlin, pp 251-278
`Higuchi, T. (1961) Rate of release of medicaments from ointment
`bases containing drugs in suspension. J . Pharm. Sci. 50: 874-875
`Lehmann, K. (1997) Chemistry and application properties of poly-
`methacrylate coating systems. In: McGinity, J. W. (ed.) Aqueous
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`Dekker, New York, pp 101-176
`Lindner, W. D., Mtickel, J . E., Lippold, B. C. (1996) Controlled release
`of drugs from hydrocolloid embeddings. Pharmazie 51: 263-272
`Lippold, B. C. (1984) Biopharmazie. Wissenschaftliche Verlagsge-
`sellschaft, Stuttgart, pp 106-108
`Mertin, D., Lippold, B. C. (1997) In-vitro permeability of the human
`nail and of a keratin membrane from bovine hooves: influence of the
`partition coefficient octanol/water and the water solubility of drugs
`on their permeability and maximum flux. J. Pharm. Pharmacol. 49:
`30-34
`
`(1993) Ciclopiroxolamin - Wegweiser
`Nolting, S., Seebacher, C.
`topischer Mykose-Therapie, Universitatsverlag Jena, Jena
`Peppas, N. A. (1985) Analysis of Fickian and non-Fickian drug release
`from polymers. Pharm. Acta Helv. 60: 110-111
`Polak, A. (1992) Kinetics of amorolfrne in human nails. Mycoses 36:
`101-103
`Polak, A., Zaug, M. (1990) Amorolfine. In: Ryley, J. F. (ed.) Che-
`motherapy of Fungal Disease (Handbook of Experimental Pharma-
`cology, Vol. 96). Springer, Berlin, pp 505-521
`Roseman, T. J. (1972) Release of steroids from a silicone polymer. J.
`Pharm. Sci. 61: 46-50
`Roseman, T. J., Higuchi, W. I. (1970) Release of medroxyproges