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Design and evaluation of transdermal chlorpheniramine maleate drug delivery system
PHARMCEUTICA IZCTA HELVETL1E ELSEVIER
Pharmaceutics
Acta Helvetiae 70 (1995) 301-306
Design and evaluation of transdermal chlorpheniramine delivery system Vlassios Andronis
maleate drug
b, Mounir S. Mesiha a,*, Fotios M. Plakogiannis
a
aDivision of Pharmaceutics and Industrial Pharmacy, Arnold & Marie Schwartz College of Pharmacy and Health Sciences, Long Island University, University Plaza, Brooklyn, New York, NY 1120, USA b Graduate School, University of Wisconsin, Madison, WI 53706, USA Received 18 November
1994; accepted 23 August 1995
Abstract The study was to develop a transdermal therapeutic system for chlorpheniramine maleate (CPM). The diffusion characteristics of CPM were determined using Franz diffusion cells, from gelled ethanol-water solutions of CPM (5, 10, and 20%). TESTSKIN@ Living Skin Equivalent (LSE) was used to study the enhancement effect of ethanol-water solutions. The 0.6 volume fraction of ethanol gave the highest diffusion rate of CPM (J,, = 1.591 mg/cm*h). The diffusion and partition coefficient data revealed that changes in ethanol volume fraction of the vehicle and ethylene vinyl acetate (EVA) membrane characteristics directly affect CPM partitioning and diffusion across EVA membranes and EVA-pressure sensitive adhesive (PSA) laminates. The data also suggest a possible interaction of CPM with the PSA. The steady state fluxes attained with 20% CPM gel is 34 /&cm’h, which is enough to keep the drug within its therapeutic plasma levels. Keywords:
Chlorpheniramine
maleate; Transdermal
delivery;
Cultured skin diffusion;
1. Introduction Chlorpheniramine maleate (CPM) is a typical cationic amphiphilic amine drug (CAD); characterized by the hydrophobic ring structure of the molecule and the hydrophilic side chain with charged cationic amino group. The physicochemical properties of CPM are expected to be common among many other CADS; therefore it was chosen as a model drug for the present study. Specific objectives are: (1) To characterize CPM solutions in ethanol water cosolvent systems. (2) To determine permeation and diffusion coefficients of CPM in TESTSKIN@ LSE, EVA membranes, and the acrylic pressure sensitive adhesive (PSA); and to study the effects of ethanol volume fraction
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author.
Tel.:
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(718)
4881633;
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0031-6865/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0031-6865(95)00035-6
Ethanol gel; Living skin equivalent
in the donor compartment, effect of gelling, and the effect of lamination with PSA. (3) To determine the apparent partition coefficients for CPM between ethanol-water solutions and EVA, EVA-PSA laminates, and (4) To develop a transdermal therapeutic system (TTS) on the basis of the above date.
2. Experimental
procedures
2.1. Materials The following chemicals were used as received: CPM from Sigma Chemical Company, St. Louis, MO. Ethanol from Fisher Scientific Company, Fairlawn, NJ. Hydroxypropyl cellulose (Klucel@) from Hercules Inc., Wilmington, DE, USA. Gentamicin sulfate from Fluka Chemical Company. Ethylene Vinyl Acetate copolymer membranes
V. Andronis et al./Pharmaceutica
302
(Co Trane controlled caliper membranes), Acrylic pressure sensitive adhesive, backing and release liner were from 3M. TESTSKIN@ Living Skin Equivalent from Organogenesis Inc.(Cambridge, MA, USA). 2.2. Equipment Franz-Chin diffusion cells and console from Crown Bioscientific Inc., Somerville, NJ. UV-Vis Spectrophotometer (Lambda-4B) from Perkin Elmer Company. HPLC from Herbert Kuauer GmbH, Berlin. 2.3. Solubility studies CPM saturation solubilities in ethanol-water cosolvent mixtures were determined as a function of ethanol volume fraction. Excess powder CPM was added to the cosolvent, stirred and the pH was adjusted to 5.5. The resulting suspensions were gently agitated in Teflon@-capped centrifuge tubes using a constant temperature water bath shaker, for 24 hours. The suspensions were allowed to settle at 32°C. Aliquots of the clear supematant solution were withdrawn by means of a syringe fitted with a 0.2 pm cellulose filter. After dilution, the triplicate solution samples were assayed for drug content spectrophotometritally at 260.9 nm. 2.4. Apparent partition
coeficient
determination
The EVA/ethanol-water apparent partition coefficients of CPM were determined as follows: Accurately measured 4 ml 0.1 mM CPM solution in ethanol-water was added to an accurately weighed EVA membrane in a borosilicate glass vials with Teflon@ cap liners. The solutions were stirred by means of a small Teflon@ coated magnet at 32°C for a period of 48 h. Aliquots were then withdrawn for analysis, using an HPLC method (Washburn 1988). The apparent partition coefficients K, were deduced from Eq. (1) K, =
( C, -
C,) V,,,/ds,*/C,Ws,*
(1)
where C, is the initial concentration of CPM in solution, C, is the equilibrium concentration of CPM in solution, VSO,is the volume of CPM-containing solution, W,,, is the weight of EVA membrane, and d,,, is the density of the EVA membranes.
Acta Heluetiae 70 (1995) 301-306
stirring ethanol-water mixture. The pH of the solution was adjusted to pH 7.0 by adding 1 N NaOH solution. The polymer powder was very slowly shifted into the vortex of the stirring solution at 200 rpm. The gelled solution was then stirred for an additional hour at 700 rpm. The finished gel was allowed to stand overnight to remove entrapped air. All the gelled solutions were prepared the day immediately preceding the diffusion experiments. 2.6. In vitro release studies All the in vitro release studies were carried out in Franz diffusion cells having 15 mm diameter and 1.76 cm* diffusional area. The receptor compartment was maintained at 37°C by means of a water bath, circulator, and a jacket surrounding the cell. The cells were filled with freshly prepared isotonic phosphate buffer of pH 7.4. The solution in the receptor compartment was continuously stirred at 600 rpm by means of Teflon@ coated magnetic stirrer, in order to avoid diffusion layer effects. The membranes were mounted between the donor and receptor compartment and secured in place by means of a clamp. Three ml of CPM solution or gel was placed in the donor compartment by means of a constant volume pipette and weight transferred each time was accurately measured. The donor compartment and the sample port were sealed with parafilm. Aliquots were removed from the receptor compartment by means of a syringe and replaced immediately with the same volume of buffer solution kept at 37°C. The samples were transferred to volumetric flasks, stored in a refrigerator until they were analysed at the end of each experiment. Sampling schedule was 1, 2, 4, 6, 8, 12, 24, 36, and 48 h. Samples were analysed spectrophotometritally at 260.9 nm for CPM content. All experiments were carried out in triplicates. Cellulose membrane was soaked overnight in the release medium to remove traces of sodium azide which is used by the manufacturer as a preservative. TESTSKIN@ LSE was stored in an incubator at 36°C the special packing in which it was shipped was opened immediately prior to use. Gentamycin sulfate, 50 pg/ml, was used to prevent microbial growth. A special donor cell was supplied with the LSE and was used instead of the standard donor compartment, using the same volume as previously indicated and with a diffusion area of 0.5 cm*. 2.7. Preparation
2.5. Preparation
of the transdermal
devices
of gels
All gel formulations were prepared to contain 5, 10, or 20% of the drug and 1 or 1.5% of the polymer. The accurately weighed drug was shifted to the vortex of
A ready made backing material with a reservoir chamber and an adhesive ring was used as the basis of the transdermal device. Three ml of a 20% CPM solution in ethanol:water (1:l v/v>, gelled with 1% HPC was placed
V. Andronis et al. /Pharmaceutics
Acta Helvetiae 70 (1995) 301-306
into the reservoir chamber and the EVA membranes (19% VA and 50 pm thickness) was placed on the top. The adhesive release liner laminate was applied to the EVA membrane and secured in place by applying manual pressure. The devices were prepared one day before the experiment. 2.8. Statistical
303
25-
treatment of the data
All the data were analyzed using the Minitab statistical program. One way Analysis of Variance (ANOVA) was used. All assumptions hold valid. The means of different populations have been compared. The purpose of the analysis is to find out if the populations have the same mean. Variations among means may be the result of either variations due to different treatments or to experimental error. If variation among treatments is much greater than variation due to experimental error, the means differ significantly. This is determined by comparing the F values obtained from the mean sum of squares of the treatment and the experimental error with the F value obtained from the statistical tables for 95% confidence interval, for the number of degrees of freedom of the treatment and the experimental error, respectively.
3. Results and discussion The donor reservoirs used in the present study have four components: CPM, ethanol, water and the hydroxypropyl cellulose (HPC). To characterize the system at skin temperature (32”(Z), it is necessary to determine the activities of all components as a function of concentration. CPM is at saturation concentration (unit activity) in the study
Time (h) Fig. 2. Effect of ethanol volume fraction on the diffusion of CPM across TESTSKIN”. Key: ethanol volume fraction, (0) 0; (0) 0.4; (w) 0.5; (0) 0.6; and (A) 1.0.
utilizing TESTSKIN@ and at lower concentrations (fraction of unit activity) in the studies utilizing EVA membranes. While the activities of ethanol and water have not been measured from these solutions, these activities are known for aqueous ethanol. It is assumed that the CPM and HPC present do not cause larger changes in the ethanol and water activities (Washburn, 1988). The saturation solubility of CPM in aqueous ethanol solutions at 32°C and pH of 5.5 are shown in Fig. 1. The parabolic shape of the curve indicates that this is a semipolar drug (Martin et al., 1983). The increase in the solubility of the drug due to ethanol cosolvent effect appear to be of only one order of magnitude larger than the aqueous solubility, a fact that indicates strong crystalline interactions and is supported by the large heat of fusion values of CPM (Martin et al., 1983). Permeation profiles of CPM through TESTSKIN@ LSE from saturated ethanol-water solutions are shown in Fig. 2 and the associated physicochemical parameters in Table 1. The use of saturated solutions of CPM differentiates the influence of solubility on CPM permeation. CPM is more
Table 1 Effect of ethanol volume fraction in the donor cell on CPM physicochemical parameters in TESTSKIN@ LSE
100’ 0.0
’
s
’
’
’
0.2 0.4 0.6 0.8 I.O Ethanol volume fraction
Fig. 1. Effect of ethanol volume fraction on the solubility of CPM.
Ethanol fraction
JSS
0 (water) 0.4 0.5 0.6 1 (ethanol)
0.948 1.389 1.411 1.591 0.652
( *g/cm*
P ([cm/h]X h) 5.488 3.347 3.370 3.775 3.252
103)
304
V. Andronis et al. /Pharmaceutics
0
IO
20 30 Time (h)
40
Acta Helvetiae 70 (1995) 301-306
50 Time (h)
Fig. 3. Effect of ethanol volume fraction on the diffusion of CPM across EVA membranes. Key: ethanol volume fraction, (0) 0.4; (0) 0.5; and (m) 0.6.
Fig. 4. Effect of vinyl acetate content of the EVA membranes on the diffusion of CPM across the membranes. Key: VA content, (0) 4.5%, (0) 9.0%. and (w) 19.0%.
soluble in the 0.6 ethanol volume fraction solution relative to water which is reflected in the increased flux from that solution in vitro. The ANOVA analysis of data showed that there are significant differences between the flux values since calculated F values from the treatment and experimental error are higher than the F 0.95 values from statistical tables. The calculated permeability coefficients, P, enable us to differentiate the effect of ethanol volume fraction in the donor solution on CPM permeation. The permeability coefficient decreases in pure ethanol compared to water. This is in agreement with the data of Pershing et al. (1990) and Good et al. (1985), who observed that ethanol decreases P values for the diffusion of P-estradiol through human skin presumably due to a corresponding decrease in the apparent partition coefficient (K,). Permeation profiles of CPM through EVA membranes (19% VA content and 50 pm thickness) are shown in Fig. 3, the associated physicochemical parameters are shown in Table 2, from a 5% CPM solution gelled with 1% HPC containing different ethanol volume fractions. Permeability coefficients increased by increasing ethanol volume frac-
tion for the vehicles tested. The fact that ethanol plasticizes the EVA membrane is highly possible (Berner et al., 1989 and Maurin et al., 1992). Furthermore, the partitioning data indicate that CPM partitioning within the EVA membrane increases for vehicles with higher ethanol content. It is possible that ethanol within the copolymer acts as a cosolvent for CPM, and so enhances partitioning of CPM into the EVA membrane. Permeation profiles of CPM through EVA membranes of different vinyl acetate contents (4.5%, 9%, 19% VA and 50 pm thickness) are shown in Fig. 4, the associated physicochemical parameters are shown in Table 3, from a 5% CPM solution gelled with 1% HPC containing ethanol (0.5 volume fraction). Permeability coefficients increased by increasing VA content of the membrane. The ANOVA analysis showed that the calculated F values from the treatment was 546.24, which is significantly (p < 0.005) higher than the F 0.95 values from statistical tables (5.14). Increasing vinyl acetate content of the EVA membrane results in reduction of crystallinity and greater elasticity of the polymer (Knapczyk and Simon, 1992). The relative increase in VA content significantly increased the K,
Table 2 Effect of ethanol volume fraction in the donor cell on CPM physicochemical parameters in EVA membranes
Table 3 Effect of vinyl acetate content of the membrane parameters in EVA membranes
Ethanol fraction
J,, pg/cm’h
icm/hI
VAc (o/o)
0.4 0.5 0.6
12.982 15.420 15.920
1.298 1.542 1.592
K, X 106)
icm,h] 3.779 4.025 4.396
3.434 3.831 3.621
X 10’)
4.5 9.0 19.0
JSS ( pg/cm’h) 2.876 4.058 15.693
([cm/h]
X
p
on CPM physicochemical
%
lo’? 0.287 0.405 1.569
([cm/h] 0.951 2.454 4.025
X
D 10’) 3.017 1.650 3.898
V. Andronis et al. /Pharmaceutics
values (Table 3). probably because of increased dipole-dipole interaction between the cationic CPM and the carboxylic group of VA polymer. Permeation profiles of 5% CPM solution gelled with 5% HPC containing 0.5 volume fraction of ethanol through EVA membranes of different thickness (19% VA content and 50 pm, 75 pm, and 100 pm) were determined and their physicochemical parameters are shown in Table 4. Permeability, diffusion, and apparent partition coefficients, as can be observed from Table 4, are close for the three different membranes tested. However, there is a decrease in the steady state flux for the membranes with higher thickness, which can be explained by assuming these fluxes are not indeed steady state fluxes. Therefore, Eq. (2) is in effect (Alberty and Hadgraft, 1979a, b). M t = 8M m,rr-‘/*r3/*exp(
-r/4)
(2)
where M,, is the amount of drug which penetrates at time t; Mm, is the total amount of drug in the donor compartment, and 7, is a normalized time. From a theoretical point of view, the only justified difference could be a difference in lag times, t,, until a steady state diffusion exists. Furthermore, it was found that by increasing the gelling agent HPC to 1.5% (while everything else remains constant) the J,, decreased to 6.837, the P value to 0.683 and D to 1.698. There are two possible ways that the gel can control the release of CPM. First, by resisting the diffusion of drug molecule through the polymer chains network, and second, by obstructing drug release through the adsorption of HPC polymer on the EVA surface. An analysis of both phenomena is not trivial. The diffusion coefficient of a solute in a gel is inversely related through the Stokes-Einstein equation to the viscosity of the gel. It has been proposed that the microviscosity of a gel is better correlated to the diffusion coefficient rather than the bulk viscosity (Khamis et al., 1986). The primary diffusion resistance can exist at the HPC-EVA interface. It is well known that the density and thickness of the adsorption layer is a function of polymer concentration in the solution among other factors. One or more of the proposed mechanisms can be responsible for the decreased release of CPM from gels with higher HPC concentrations.
Table 4 Effect of membrane EVA membranes Thickness
(wd 50 75 100
thickness
JS3 ( pg/cm* h) 14.429 10.878 8.182
on CPM physicochemical
([cm/h]
p
X lo61
%
1.442 4.025 1.631 4.025 1.636 4.025
parameters
([cm/h]
X I$ 3.582 4.052 4.064
in
Acta Helvetiae 70 (I 995) 301-306
305
Table 5 Effect of CPM concentration in the donor chemical paramets in EVA-PSA laminates
JES
CPM (o/o)
( pg/cm*h)
5 10 20
5.851 16.270 30.876
([cm/h]
cell on the CPM physico-
p
KP
1.287 1.789 1.698
5.482 5.482 5.482
X lo61
([cm/h]
D X 10’1 2.347 3.263 3.097
The permeation profiles of CPM through EVA membrane (19% VA, 50 pm thickness&Adhesive laminate as a function of CPM concentration were evaluated and the associated physicochemical parameters are shown in Table 5. The CPM flux increases with increasing CPM concentration, in agreement with diffusion theory. The study shows that CPM flux from the 20% CPM gel is close to the target flux. Using the published data (Williams et al., 1991) for effective therapeutic plasma concentration: C, = 60 ng/ml; volume of distribution: Vd= 222 1; elimination rate from the plasma: K,, = 0.038 hh’ ; and also assuming that the area of applicable system is 15 cm*, the calculate the target flux will be 34 g/cm*h, using Eq. (3).
(3) By comparing CPM fluxes through EVA membranes and the EVA - Adhesive laminates for the same CPM concentration, we observe a decrease in flux, permeability coefficients and diffusion coefficients, and an increase in apparent partition coefficients. This can be explained if we speculate a possible interaction to exist between the acrylic acid polymer and the cationic CPM that results in increased partitioning to the adhesive laminate.
References Alberty, W.J. and Hadgraft, J. (1979) Percutaneous absorption: Theoretical description. J. Pharm. Pharmacol. 31, 129-139. Alberty, W.J. and Hadgraft, J. (19791 Percutaneous absorption: In vivo experiments. J. Pharm. Pharmacol. 31, 140-147. Berner, B, Ohe, J.H., Mazzenga, G.C., Steffens, R.J. and Ebert, C.D. (1989) Ethanol:water mutually enhanced transdennal therapeutic system II. Skin perrmeation of ethanol and nitroglycerin. J. Pharm. Sci. 78, 314-318. Good, W.R., Powers, M.S., Campbell, P, and Schenker, L. (1985) A new transdermal delivery system for estradiol. J. Control. Rel. 2, 89-97. Khamis, K.I., Davis, S.S., and Hadgraft, J. (1986) Microviscosity and drug release from topical gel formulations, Pharm. Res. 81, 214-218. Knapczyk, J.K. and Simon, R.H.M. (19921 In Kent, J.A. (Ed.), Riegel’s Industrial Chemistry, VNR, New York, 1992, p 640. Martin, A., Swarbrick, J., and Cammarata, A., Eds. (19831 Physical Pharmacy, Lea & Febiger, Philadelphia, PA, p. 283. Maurin, M.B., Dittert, L.W., and Hussain, A.A. (1992) Mechanism of
306
V. Andronis et al. /Pharmaceutics
diffusion of monosubstituted benzoic acid through ethylen vinyl acetate copolymers. J. Pharm. Sci. 81, 79-84. Pershing, L.K., Lambert, L.D., Knuston, K. (1990) Mechanism of ethanol-enhanced estradiol permeation across human skin in vivo. Pharm. Res. 7, 170-175. Washburn, E.W., Ed. (19881, International Critical Tables of Numerical
Acta Helvetiae 70 (1995) 301-306 Data, Physics, Chemistry and Technology, Vol. III, McGraw-Hill, New York, p. 290. Williams, R.L., Lipton, R.A., Braun, R.L., Lim, E.T., Liang Gee, W. and Leeson, L.J. (1991) Development of a new controlled release formulation of chlorpheniramine maleate using in vitro-in vivo correlations. J. Pharm. Sci. 80, 22-29.
Pharmaceutics
Acta Helvetiae 70 (1995) 301-306
Design and evaluation of transdermal chlorpheniramine delivery system Vlassios Andronis
maleate drug
b, Mounir S. Mesiha a,*, Fotios M. Plakogiannis
a
aDivision of Pharmaceutics and Industrial Pharmacy, Arnold & Marie Schwartz College of Pharmacy and Health Sciences, Long Island University, University Plaza, Brooklyn, New York, NY 1120, USA b Graduate School, University of Wisconsin, Madison, WI 53706, USA Received 18 November
1994; accepted 23 August 1995
Abstract The study was to develop a transdermal therapeutic system for chlorpheniramine maleate (CPM). The diffusion characteristics of CPM were determined using Franz diffusion cells, from gelled ethanol-water solutions of CPM (5, 10, and 20%). TESTSKIN@ Living Skin Equivalent (LSE) was used to study the enhancement effect of ethanol-water solutions. The 0.6 volume fraction of ethanol gave the highest diffusion rate of CPM (J,, = 1.591 mg/cm*h). The diffusion and partition coefficient data revealed that changes in ethanol volume fraction of the vehicle and ethylene vinyl acetate (EVA) membrane characteristics directly affect CPM partitioning and diffusion across EVA membranes and EVA-pressure sensitive adhesive (PSA) laminates. The data also suggest a possible interaction of CPM with the PSA. The steady state fluxes attained with 20% CPM gel is 34 /&cm’h, which is enough to keep the drug within its therapeutic plasma levels. Keywords:
Chlorpheniramine
maleate; Transdermal
delivery;
Cultured skin diffusion;
1. Introduction Chlorpheniramine maleate (CPM) is a typical cationic amphiphilic amine drug (CAD); characterized by the hydrophobic ring structure of the molecule and the hydrophilic side chain with charged cationic amino group. The physicochemical properties of CPM are expected to be common among many other CADS; therefore it was chosen as a model drug for the present study. Specific objectives are: (1) To characterize CPM solutions in ethanol water cosolvent systems. (2) To determine permeation and diffusion coefficients of CPM in TESTSKIN@ LSE, EVA membranes, and the acrylic pressure sensitive adhesive (PSA); and to study the effects of ethanol volume fraction
* Corresponding 4883437.
author.
Tel.:
+l
(718)
4881633;
fax:
+ 1 (718)
0031-6865/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0031-6865(95)00035-6
Ethanol gel; Living skin equivalent
in the donor compartment, effect of gelling, and the effect of lamination with PSA. (3) To determine the apparent partition coefficients for CPM between ethanol-water solutions and EVA, EVA-PSA laminates, and (4) To develop a transdermal therapeutic system (TTS) on the basis of the above date.
2. Experimental
procedures
2.1. Materials The following chemicals were used as received: CPM from Sigma Chemical Company, St. Louis, MO. Ethanol from Fisher Scientific Company, Fairlawn, NJ. Hydroxypropyl cellulose (Klucel@) from Hercules Inc., Wilmington, DE, USA. Gentamicin sulfate from Fluka Chemical Company. Ethylene Vinyl Acetate copolymer membranes
V. Andronis et al./Pharmaceutica
302
(Co Trane controlled caliper membranes), Acrylic pressure sensitive adhesive, backing and release liner were from 3M. TESTSKIN@ Living Skin Equivalent from Organogenesis Inc.(Cambridge, MA, USA). 2.2. Equipment Franz-Chin diffusion cells and console from Crown Bioscientific Inc., Somerville, NJ. UV-Vis Spectrophotometer (Lambda-4B) from Perkin Elmer Company. HPLC from Herbert Kuauer GmbH, Berlin. 2.3. Solubility studies CPM saturation solubilities in ethanol-water cosolvent mixtures were determined as a function of ethanol volume fraction. Excess powder CPM was added to the cosolvent, stirred and the pH was adjusted to 5.5. The resulting suspensions were gently agitated in Teflon@-capped centrifuge tubes using a constant temperature water bath shaker, for 24 hours. The suspensions were allowed to settle at 32°C. Aliquots of the clear supematant solution were withdrawn by means of a syringe fitted with a 0.2 pm cellulose filter. After dilution, the triplicate solution samples were assayed for drug content spectrophotometritally at 260.9 nm. 2.4. Apparent partition
coeficient
determination
The EVA/ethanol-water apparent partition coefficients of CPM were determined as follows: Accurately measured 4 ml 0.1 mM CPM solution in ethanol-water was added to an accurately weighed EVA membrane in a borosilicate glass vials with Teflon@ cap liners. The solutions were stirred by means of a small Teflon@ coated magnet at 32°C for a period of 48 h. Aliquots were then withdrawn for analysis, using an HPLC method (Washburn 1988). The apparent partition coefficients K, were deduced from Eq. (1) K, =
( C, -
C,) V,,,/ds,*/C,Ws,*
(1)
where C, is the initial concentration of CPM in solution, C, is the equilibrium concentration of CPM in solution, VSO,is the volume of CPM-containing solution, W,,, is the weight of EVA membrane, and d,,, is the density of the EVA membranes.
Acta Heluetiae 70 (1995) 301-306
stirring ethanol-water mixture. The pH of the solution was adjusted to pH 7.0 by adding 1 N NaOH solution. The polymer powder was very slowly shifted into the vortex of the stirring solution at 200 rpm. The gelled solution was then stirred for an additional hour at 700 rpm. The finished gel was allowed to stand overnight to remove entrapped air. All the gelled solutions were prepared the day immediately preceding the diffusion experiments. 2.6. In vitro release studies All the in vitro release studies were carried out in Franz diffusion cells having 15 mm diameter and 1.76 cm* diffusional area. The receptor compartment was maintained at 37°C by means of a water bath, circulator, and a jacket surrounding the cell. The cells were filled with freshly prepared isotonic phosphate buffer of pH 7.4. The solution in the receptor compartment was continuously stirred at 600 rpm by means of Teflon@ coated magnetic stirrer, in order to avoid diffusion layer effects. The membranes were mounted between the donor and receptor compartment and secured in place by means of a clamp. Three ml of CPM solution or gel was placed in the donor compartment by means of a constant volume pipette and weight transferred each time was accurately measured. The donor compartment and the sample port were sealed with parafilm. Aliquots were removed from the receptor compartment by means of a syringe and replaced immediately with the same volume of buffer solution kept at 37°C. The samples were transferred to volumetric flasks, stored in a refrigerator until they were analysed at the end of each experiment. Sampling schedule was 1, 2, 4, 6, 8, 12, 24, 36, and 48 h. Samples were analysed spectrophotometritally at 260.9 nm for CPM content. All experiments were carried out in triplicates. Cellulose membrane was soaked overnight in the release medium to remove traces of sodium azide which is used by the manufacturer as a preservative. TESTSKIN@ LSE was stored in an incubator at 36°C the special packing in which it was shipped was opened immediately prior to use. Gentamycin sulfate, 50 pg/ml, was used to prevent microbial growth. A special donor cell was supplied with the LSE and was used instead of the standard donor compartment, using the same volume as previously indicated and with a diffusion area of 0.5 cm*. 2.7. Preparation
2.5. Preparation
of the transdermal
devices
of gels
All gel formulations were prepared to contain 5, 10, or 20% of the drug and 1 or 1.5% of the polymer. The accurately weighed drug was shifted to the vortex of
A ready made backing material with a reservoir chamber and an adhesive ring was used as the basis of the transdermal device. Three ml of a 20% CPM solution in ethanol:water (1:l v/v>, gelled with 1% HPC was placed
V. Andronis et al. /Pharmaceutics
Acta Helvetiae 70 (1995) 301-306
into the reservoir chamber and the EVA membranes (19% VA and 50 pm thickness) was placed on the top. The adhesive release liner laminate was applied to the EVA membrane and secured in place by applying manual pressure. The devices were prepared one day before the experiment. 2.8. Statistical
303
25-
treatment of the data
All the data were analyzed using the Minitab statistical program. One way Analysis of Variance (ANOVA) was used. All assumptions hold valid. The means of different populations have been compared. The purpose of the analysis is to find out if the populations have the same mean. Variations among means may be the result of either variations due to different treatments or to experimental error. If variation among treatments is much greater than variation due to experimental error, the means differ significantly. This is determined by comparing the F values obtained from the mean sum of squares of the treatment and the experimental error with the F value obtained from the statistical tables for 95% confidence interval, for the number of degrees of freedom of the treatment and the experimental error, respectively.
3. Results and discussion The donor reservoirs used in the present study have four components: CPM, ethanol, water and the hydroxypropyl cellulose (HPC). To characterize the system at skin temperature (32”(Z), it is necessary to determine the activities of all components as a function of concentration. CPM is at saturation concentration (unit activity) in the study
Time (h) Fig. 2. Effect of ethanol volume fraction on the diffusion of CPM across TESTSKIN”. Key: ethanol volume fraction, (0) 0; (0) 0.4; (w) 0.5; (0) 0.6; and (A) 1.0.
utilizing TESTSKIN@ and at lower concentrations (fraction of unit activity) in the studies utilizing EVA membranes. While the activities of ethanol and water have not been measured from these solutions, these activities are known for aqueous ethanol. It is assumed that the CPM and HPC present do not cause larger changes in the ethanol and water activities (Washburn, 1988). The saturation solubility of CPM in aqueous ethanol solutions at 32°C and pH of 5.5 are shown in Fig. 1. The parabolic shape of the curve indicates that this is a semipolar drug (Martin et al., 1983). The increase in the solubility of the drug due to ethanol cosolvent effect appear to be of only one order of magnitude larger than the aqueous solubility, a fact that indicates strong crystalline interactions and is supported by the large heat of fusion values of CPM (Martin et al., 1983). Permeation profiles of CPM through TESTSKIN@ LSE from saturated ethanol-water solutions are shown in Fig. 2 and the associated physicochemical parameters in Table 1. The use of saturated solutions of CPM differentiates the influence of solubility on CPM permeation. CPM is more
Table 1 Effect of ethanol volume fraction in the donor cell on CPM physicochemical parameters in TESTSKIN@ LSE
100’ 0.0
’
s
’
’
’
0.2 0.4 0.6 0.8 I.O Ethanol volume fraction
Fig. 1. Effect of ethanol volume fraction on the solubility of CPM.
Ethanol fraction
JSS
0 (water) 0.4 0.5 0.6 1 (ethanol)
0.948 1.389 1.411 1.591 0.652
( *g/cm*
P ([cm/h]X h) 5.488 3.347 3.370 3.775 3.252
103)
304
V. Andronis et al. /Pharmaceutics
0
IO
20 30 Time (h)
40
Acta Helvetiae 70 (1995) 301-306
50 Time (h)
Fig. 3. Effect of ethanol volume fraction on the diffusion of CPM across EVA membranes. Key: ethanol volume fraction, (0) 0.4; (0) 0.5; and (m) 0.6.
Fig. 4. Effect of vinyl acetate content of the EVA membranes on the diffusion of CPM across the membranes. Key: VA content, (0) 4.5%, (0) 9.0%. and (w) 19.0%.
soluble in the 0.6 ethanol volume fraction solution relative to water which is reflected in the increased flux from that solution in vitro. The ANOVA analysis of data showed that there are significant differences between the flux values since calculated F values from the treatment and experimental error are higher than the F 0.95 values from statistical tables. The calculated permeability coefficients, P, enable us to differentiate the effect of ethanol volume fraction in the donor solution on CPM permeation. The permeability coefficient decreases in pure ethanol compared to water. This is in agreement with the data of Pershing et al. (1990) and Good et al. (1985), who observed that ethanol decreases P values for the diffusion of P-estradiol through human skin presumably due to a corresponding decrease in the apparent partition coefficient (K,). Permeation profiles of CPM through EVA membranes (19% VA content and 50 pm thickness) are shown in Fig. 3, the associated physicochemical parameters are shown in Table 2, from a 5% CPM solution gelled with 1% HPC containing different ethanol volume fractions. Permeability coefficients increased by increasing ethanol volume frac-
tion for the vehicles tested. The fact that ethanol plasticizes the EVA membrane is highly possible (Berner et al., 1989 and Maurin et al., 1992). Furthermore, the partitioning data indicate that CPM partitioning within the EVA membrane increases for vehicles with higher ethanol content. It is possible that ethanol within the copolymer acts as a cosolvent for CPM, and so enhances partitioning of CPM into the EVA membrane. Permeation profiles of CPM through EVA membranes of different vinyl acetate contents (4.5%, 9%, 19% VA and 50 pm thickness) are shown in Fig. 4, the associated physicochemical parameters are shown in Table 3, from a 5% CPM solution gelled with 1% HPC containing ethanol (0.5 volume fraction). Permeability coefficients increased by increasing VA content of the membrane. The ANOVA analysis showed that the calculated F values from the treatment was 546.24, which is significantly (p < 0.005) higher than the F 0.95 values from statistical tables (5.14). Increasing vinyl acetate content of the EVA membrane results in reduction of crystallinity and greater elasticity of the polymer (Knapczyk and Simon, 1992). The relative increase in VA content significantly increased the K,
Table 2 Effect of ethanol volume fraction in the donor cell on CPM physicochemical parameters in EVA membranes
Table 3 Effect of vinyl acetate content of the membrane parameters in EVA membranes
Ethanol fraction
J,, pg/cm’h
icm/hI
VAc (o/o)
0.4 0.5 0.6
12.982 15.420 15.920
1.298 1.542 1.592
K, X 106)
icm,h] 3.779 4.025 4.396
3.434 3.831 3.621
X 10’)
4.5 9.0 19.0
JSS ( pg/cm’h) 2.876 4.058 15.693
([cm/h]
X
p
on CPM physicochemical
%
lo’? 0.287 0.405 1.569
([cm/h] 0.951 2.454 4.025
X
D 10’) 3.017 1.650 3.898
V. Andronis et al. /Pharmaceutics
values (Table 3). probably because of increased dipole-dipole interaction between the cationic CPM and the carboxylic group of VA polymer. Permeation profiles of 5% CPM solution gelled with 5% HPC containing 0.5 volume fraction of ethanol through EVA membranes of different thickness (19% VA content and 50 pm, 75 pm, and 100 pm) were determined and their physicochemical parameters are shown in Table 4. Permeability, diffusion, and apparent partition coefficients, as can be observed from Table 4, are close for the three different membranes tested. However, there is a decrease in the steady state flux for the membranes with higher thickness, which can be explained by assuming these fluxes are not indeed steady state fluxes. Therefore, Eq. (2) is in effect (Alberty and Hadgraft, 1979a, b). M t = 8M m,rr-‘/*r3/*exp(
-r/4)
(2)
where M,, is the amount of drug which penetrates at time t; Mm, is the total amount of drug in the donor compartment, and 7, is a normalized time. From a theoretical point of view, the only justified difference could be a difference in lag times, t,, until a steady state diffusion exists. Furthermore, it was found that by increasing the gelling agent HPC to 1.5% (while everything else remains constant) the J,, decreased to 6.837, the P value to 0.683 and D to 1.698. There are two possible ways that the gel can control the release of CPM. First, by resisting the diffusion of drug molecule through the polymer chains network, and second, by obstructing drug release through the adsorption of HPC polymer on the EVA surface. An analysis of both phenomena is not trivial. The diffusion coefficient of a solute in a gel is inversely related through the Stokes-Einstein equation to the viscosity of the gel. It has been proposed that the microviscosity of a gel is better correlated to the diffusion coefficient rather than the bulk viscosity (Khamis et al., 1986). The primary diffusion resistance can exist at the HPC-EVA interface. It is well known that the density and thickness of the adsorption layer is a function of polymer concentration in the solution among other factors. One or more of the proposed mechanisms can be responsible for the decreased release of CPM from gels with higher HPC concentrations.
Table 4 Effect of membrane EVA membranes Thickness
(wd 50 75 100
thickness
JS3 ( pg/cm* h) 14.429 10.878 8.182
on CPM physicochemical
([cm/h]
p
X lo61
%
1.442 4.025 1.631 4.025 1.636 4.025
parameters
([cm/h]
X I$ 3.582 4.052 4.064
in
Acta Helvetiae 70 (I 995) 301-306
305
Table 5 Effect of CPM concentration in the donor chemical paramets in EVA-PSA laminates
JES
CPM (o/o)
( pg/cm*h)
5 10 20
5.851 16.270 30.876
([cm/h]
cell on the CPM physico-
p
KP
1.287 1.789 1.698
5.482 5.482 5.482
X lo61
([cm/h]
D X 10’1 2.347 3.263 3.097
The permeation profiles of CPM through EVA membrane (19% VA, 50 pm thickness&Adhesive laminate as a function of CPM concentration were evaluated and the associated physicochemical parameters are shown in Table 5. The CPM flux increases with increasing CPM concentration, in agreement with diffusion theory. The study shows that CPM flux from the 20% CPM gel is close to the target flux. Using the published data (Williams et al., 1991) for effective therapeutic plasma concentration: C, = 60 ng/ml; volume of distribution: Vd= 222 1; elimination rate from the plasma: K,, = 0.038 hh’ ; and also assuming that the area of applicable system is 15 cm*, the calculate the target flux will be 34 g/cm*h, using Eq. (3).
(3) By comparing CPM fluxes through EVA membranes and the EVA - Adhesive laminates for the same CPM concentration, we observe a decrease in flux, permeability coefficients and diffusion coefficients, and an increase in apparent partition coefficients. This can be explained if we speculate a possible interaction to exist between the acrylic acid polymer and the cationic CPM that results in increased partitioning to the adhesive laminate.
References Alberty, W.J. and Hadgraft, J. (1979) Percutaneous absorption: Theoretical description. J. Pharm. Pharmacol. 31, 129-139. Alberty, W.J. and Hadgraft, J. (19791 Percutaneous absorption: In vivo experiments. J. Pharm. Pharmacol. 31, 140-147. Berner, B, Ohe, J.H., Mazzenga, G.C., Steffens, R.J. and Ebert, C.D. (1989) Ethanol:water mutually enhanced transdennal therapeutic system II. Skin perrmeation of ethanol and nitroglycerin. J. Pharm. Sci. 78, 314-318. Good, W.R., Powers, M.S., Campbell, P, and Schenker, L. (1985) A new transdermal delivery system for estradiol. J. Control. Rel. 2, 89-97. Khamis, K.I., Davis, S.S., and Hadgraft, J. (1986) Microviscosity and drug release from topical gel formulations, Pharm. Res. 81, 214-218. Knapczyk, J.K. and Simon, R.H.M. (19921 In Kent, J.A. (Ed.), Riegel’s Industrial Chemistry, VNR, New York, 1992, p 640. Martin, A., Swarbrick, J., and Cammarata, A., Eds. (19831 Physical Pharmacy, Lea & Febiger, Philadelphia, PA, p. 283. Maurin, M.B., Dittert, L.W., and Hussain, A.A. (1992) Mechanism of
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diffusion of monosubstituted benzoic acid through ethylen vinyl acetate copolymers. J. Pharm. Sci. 81, 79-84. Pershing, L.K., Lambert, L.D., Knuston, K. (1990) Mechanism of ethanol-enhanced estradiol permeation across human skin in vivo. Pharm. Res. 7, 170-175. Washburn, E.W., Ed. (19881, International Critical Tables of Numerical
Acta Helvetiae 70 (1995) 301-306 Data, Physics, Chemistry and Technology, Vol. III, McGraw-Hill, New York, p. 290. Williams, R.L., Lipton, R.A., Braun, R.L., Lim, E.T., Liang Gee, W. and Leeson, L.J. (1991) Development of a new controlled release formulation of chlorpheniramine maleate using in vitro-in vivo correlations. J. Pharm. Sci. 80, 22-29.