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Relationship between In Vivo Skin Blanching and In Vitro Release Rate for Betamethasone Valerate Creams
Relationship between In Vivo Skin Blanching and In Vitro Release Rate for Betamethasone Valerate Creams VlNOD
P. SHAH*', JEROME ELKINS*,
AND
JEROME P. SKELLY'
Received December 3,1990, from the 'Center for D N Evaluation ~ and Research, Food and DN Administration, Rockville, MD 20857, and Accepted for pu%cation March 13, 1991. 'Dallas District Laboratory, Food and Drug Administration, Dallas, TX 75204. Abstract 0 Betamethasone valerate creams from two firms were evaluated using the skin blanching procedure. In both studies, the same
cream formulation exhibited significantly higher blanching compared to the other product. An in vitro release rate was determined for these betamethasone valerate cream products using a diffusion cell system, with a cellulose acetate membrane and a 60% ethano1:water receptor medium. The release rate (flux) of betamethasone valerate was higher for the higher blanching formulation and was statistically different from the other product.The integrity of the cellulose acetate membrane in 60% ethanokwater mixture was ascertained using hydrocortisone cream product. The in vitro drug release method, using a diffusion cell system and a synthetic membrane, can serve as a good quality control test method for topical creams.
Glucocorticoids, when applied to the skin, exert a specific pharmacologicalresponse that is evident as skin blanching.l.2 This pharmaccdynamic response depends on the potency of the steroid and the drug release properties from the formulation, as well as the resultant pharmacokinetic behavior of the drug in the skin. For a topical cream product to be effective, it must first release the active drug from ita formulation. Measuring the drug release, therefore, may provide a useful and a meaningful method as a quality control test procedure. Shah et al. have developed a simple, reliable, and reproducible test procedure to study the release rate of hydrocortisone, a water-soluble drug, from the cream preparation.3.4 The method employs a diffusion cell system with commercially available synthetic membranes. This paper describes the application of the method to study the release profile of a poorly water soluble drug, betamethasone valerate, from a cream formulation. The release rates from the two brands of betamethasone valerate cream products were also compared with the pharmacodynamic properties of the drug.
Experimental Section Cream Products-Commercially marketed creams were used in this study. The betamethasone valerate creams were 0.1% valisone cream (Schering: lot nos. 6FE507 and 8FE300), and 0.1% betamethasone valerate cream (Fougera; lot nos. 6310 and 6520). The 2.5% hydrocortisone cream was from Dermik (lot no. 73411). Synthetic Membrane-The membrane was composed of mixed cellulose esters (cellulose acetate and nitrate), was 25 mm in diameter, 0.45 pm pore size, and 150 pm (6 mils) thick (Gelman Sciences Inc.) Diffusion Cells-" standard open-capped, ground-glass Franz diffusion cell, with a 15-mm diameter orifice (1.767 cm2 area, total diameter of cell = 25 mm), was utilized. The receptor phase was stirred by means of a constantly spinning bar magnet (Varispeed cell drive console, Crown Glaes Company). Receptor Phase-Different concentrations of an ethanokwater mixture, and pH 5.0 acetate buffer (0.05 M) were used. All receptor media were deaerated before use in the study. Sample Preparation-The synthetic membrane (25 mm in diameter) was soaked in the receptor phase and removed. A 2-mm thick x 104 / Journal of Pharmaceutical Sciences Vol. 81, No. 1, January 1992
the
17-mm diameter Teflon "mask, with a 15-mm hole in the center, was centered over the synthetic membrane. This 15-mm hole corresponded to the diameter and circumference of the membrane holder on the diffusion cell. The cream sample (-300 mg) was placed in the hole and spread uniformly with a Teflon squeegee by pulling across the Teflon mask. This procedure resulted in a smooth, even film of the sample, uniform in both thickness and diameter. The "mask was removed using tweezers and the prepared sample/membrane was transferred to the diffusion cell, with the cream side facing up.' Procedure-The lower part of the diffusion cell was filled with deaerated receptor phase medium. The synthetic membrane with the cream sample in the center and the top part of the cell were placed together and checked for air bubbles. If air bubbles were present, the sample preparation and procedure was repeated. If no air bubbles were present, the cells were clamped in place. Using a Microette automated sampler (Hanson Corporation, CAI interfaced with the diffusion cell, a 150-pL aliquot was withdrawn from the middle part of the cell at 30-, 60-, 120-, 240-, and 360-min intervals and analyzed by direct injection into a HPLC system. Aliquots of 150 pL were replaced &r each sample removal. The HPLC analysis of betamethasone valerate was carried out using a UBondapak C18 column (3.9 mm i.d., 30 cm long) and a 254-nm UV detector. Samples were eluted using an isocratic mobile phase consisting of acetonitri1e:water (60:40) at ambient temperature and a flow of 1.2 mumin. Under these conditions, the retention time for betamethasone valerate was 6 min, and detection limits were 8 ng per 2 0 - 4 injection, with a 5-108 CV. The concentration (pg/mL) of betamethasone valerate in the receptor phase was calculated using a standard of known concentration. The total amount of betamethasone valerate released (concentration in @mL x volume of the receptor phase) and the amount released per unit area (pg/cm2) were calculated. Skin Blanching Experiments-The Stoughton-McKenzie test1 for glucocorticoids was carried out in normal healthy volunteers by Stoughton6 and Olsens under two separate FDA contracts. The experimental details and results are published elsewhere.7
Results and Discussion The release rate of hydrocortisone from the cream was determined using aqueous media such as pH 5 acetate buffer, pH 7.4 phosphate buffer, and normal saline solutions. However, with betamethasone valerate cream, no drug could be detected in any of these receptor media up to 24 h. This is primarily because of low solubility (0.16 mg/100 mL) of betamethasone valerate in these receptor media. Addition of surfactants, such as sodium lauryl sulfate, Valpo, etc., also did not increase in vitro release. Use of 40% PEG 400 in water does increase the solubility, and small amounts of betamethasone valerate were detected in the receptor medium (5-14 &cm2 in a 6-h period). This quantity is too small to use as a quality control method and to detect any significant differences between the cream formulations. Therefore, other aqueous organic solventa were evaluated for use as receptor medium. The simplest aqueous organic solvents, such as methanol and ethanol in different concentrations, were tried. The synthetic membrane, cellulose acetate, was found to be unstable in 100% methanol; the membrane completely disThis article not subject to US.copyright. Published 1992, American Pharmaceutical Association
integrated. On the other hand, the membrane remained intact in ethanol (95%).Some cream formulations break down on coming in contact with 95%ethanol. Therefore, the release rate profile of betamethasone valerate was studied using 25, 50, and 60% ethanol. The results plotted against the square root of time are shown in Figure 1. The amount of drug released per unit area (pg/cm2)when plotted against square root of time ( t ) results in a straight line. The slope of the line
I
6o
/
50
I I
0
-
0
5 10 15 20 SQUARE ROOT OF TIME (MINUTES) flgure 1-In vitro release rate of betamethasone valerate cream in (0) 25, (*) 50, and (x) 6090 ethanol.
which represents the release rate (i.e., steady-state flux)was calculated using linear regression. As expected, because of higher solubility, the release rate was faster with a higher concentration of ethanol. It was decided to study the release of betamethasone valerate from all cream products using a 60% ethano1:water mixture. The integrity of the synthetic membrane, mixed celluose esters, in the presence of the 60% ethano1:water mixture was ascertained by using hydrocortisone cream product. The membrane was soaked in 60% ethano1:water for 16 h, air dried, and used to determine the hydrocortisone release from the cream. In another experiment, the membrane was used without soaking in 60% ethano1:water. The results of the study given in Table I show no statistically significant difference in release rate profile, thus establishing the integrity of the membrane when exposed to the 60% ethano1:water mixture. The in vitro release rate (flux)of betamethasone valerate, using the diffusion cell system, synthetic membrane, and 60% ethano1:water as the receptor medium, from the creams is shown in Table 11. The in vitro release data were plotted against the square root of time (t)and are shown in Figure 2. The difference in slopes (steady-state flux) between the two products relates to the differences in their relative ability to release the drug under the experimental conditions. The release rates of betamethasone valerate for the two products studied were significantly different from one another; the release rate was higher and faster for the brand name product (54-56 pglcm2) compared with the generic product (45-48 pglcm2) under the testing conditions. The difference in slope (release rate) is due to the difference between the formulation of the two products studied (Le., it may be due to the source of the active ingredient or the raw materials in the vehicle phase of each cream). Even if the vehicle composition (ingredients, percentages, etc.) may be the same in each cream, the differencescould be related to the sources of raw materials or manufacturing process. The drug solubility, initial drug concentration, diffusion constant of the drug in the vehicle, and other formulation adjuvants play a
Table H n Vltro Release of Hydrocortisone from Cream'
Hydrocortisone Released, pgIcmzb
Membrane Membrane NOTsoaked in 60% ethanol Membrane soaked in 60% ethanol and dried t statisticd
Flux'
Regression Correlation Coeff lcient
30 min
60 min
120 min
240 min
360 min
20.7 (9.1) . .
40.0 (11.1)
71.8 (3.)
133.1 (3.5)
188.8 (3.1)
12.5
0.988
21.3 (3.7)
41.3
74.4 (3.1)
133.1 (3.4)
191.2 (4.3)
12.6
0.988
-
-
0.77
0.68
(2.8)
1.97
0.93
0.58
* Hydrocortisonecream (2.5%. Dermik X7341 l), diffusion cell, cellulose acetate membrane, and pH 5.0 acetate buffer. Data within parentheses represent percent coefficient of variation (n = 6). Flux = slope = pg/cm2/min0'. No difference at any time point. Table l C l n Vltro Release of Betamethasone Valerate from Creams'
Product Study I
Schering 6FE507 Fougera 6310 t statistic' Study II
Schering 8FE 300
Fougera 6520 t statisticd
Betamethasone Valerate Released, pglcm2 120 min 240 min
30 min
60 min
5.9 4.7 2.25
11.7 9.7 2.56
22.8 20.2 2.09
40.2 35.8 2.92
4.8 4.3
12.1 9.0 2.46
23.0 18.7 3.36
40.5 33.1 4.66
0.83
360 min
54.0 48.2 3.10 55.5
44.3 4.71
a Using diffusion cell, cellulose acetate membrane, and 60% ethanokwater as the receptor medium. Flux different at all time points. Significantly different at all time points except 30 min.
= slope =
Fluxb
Regression Coefficient
3.56 3.19
0.996 0.997
3.78 2.96
0.997 0.997
-
-
pg/cm2/min0'. Significantly
Journal of Pharmaceutical Sciences I 105 Vol. 81, No. 1, January 1992
Table IlCSummary of the In Vlvo Blanchlng Score for Betamethasone Vakrate Cream6 study
Number SubjectsOf
Product
I
30
II
32
Schering Fougera Schering Schering Fougera Fougera
Number
..
5 10 15 SQUARE ROOT OF TIME (MINUTES)
20
Flgure 2-In vitro release rate of two betamethasone valerate creams in 60% ethanol. Key: (*) Schering; (0)Fougera.
- 7 -R ?
3 56
2 33
SCHERING
PD
T FOUGE
IN VlTRO
PD
IN VlTRO
STUDY I
STUDY 11 Flgure 3-Correlation between pharmacodynamicresponse and in vitro release rate in 60% ethanokwater for betamethasone valerate creams. major role in affecting the drug release rate. In addition, the release rate of the drug from the cream formulation largely depends on the same manufacturing variables which influence the quality and efficacy of the preparation. Because of these reasons, the release rate can be used as a quality control measure to assure batch-to-batch uniformity. The release rates of betamethasone valerate from two batches from the same manufacturer were not significantly different (t statistics), again suggesting that the procedure can be used as a quality control method for assuring batchto-batch uniformity. For topical glucocorticoids, the “vasoconstriction” or, correctly designated, “skin blanching” test is canied out to determine the potency and bioequivalence of the product.8 In 106 I Journal of Pharmaceutical Sciences Vol. 81, No. 1, January 1992
Total Score
Average Score
70 49 72 73
2.33 1.63 2.25 2.28 1.94 2.09
62 67
two such independent studies (referred to as Study I and Study II), the skin blanching score of the brand name product was compared with a generic praduct.6.6 In study 11, the same two products were administered twice.6 Table I1 provides a summary of both in vivo study results. The total skin blanching score is a n indicator of relative response of the product. The ANOVA indicated that the difference in response between the two betamethasone valerate creams was highly significant, in both studies. Figure 3 compares the in vitro release rate of betamethasone valerate with the in vivo blanching score. The rank-order release rate obtained correlated with the blanching score of the products in both of the studies, thus adding validity to the in vitro method. The rank-ordered correlation of pharmacodynamic data (skin blanching score)with the in vitro release rate (pg/cm2/h) adds validity to the newly developed in vitro quality control test. A similar rank-order correlation was observed for hydrocortisone creams with pharmacokinetic (concentrations of drug in skin), pharmacodynamic (skin blanching score), and in vitro release rate (flux,c~@/mL/h) data.9 In spite of having a good in vitro:in vivo rank-order correlation in the case of betamethasone valerate cream and hydrocortisone cream products studied, it should be emphasized that the in vitro release test described is strictly a quality control test to assure lot-to-lot uniformity, and it should not be used to predict bioactivity. The correlation obtained between the in vitro release and in vivo performance adds strength and validity to the in vitro test. In conclusion, a simple, reliable, and reproducible method using a commercially available synthetic membrane and diffusion cell assembly has been developed and established to measure the release rate of drug, such as hydrocortisone and betamethasone valerate, from cream formulations. The validity of the method has been evaluated and confirmed. The method can be used as a quality control test to assure lot-to-lot uniformity of the product. The in vivo drug penetration and absorption process is very complex, whereas the in vitro test procedure is highly simplified. Therefore, extrapolation of the data (results) should be carried out with caution.
References and Notes 1. McKetlzie, A. W.; Stoughton, R. B. Arch. Dermatol. 1962, 86, 608410. 2. Cornell, R.C.; Stoughton, R.B. Arch. Dermatol. 1985, 121, 63-67. 3. Shah, V. P.; Elkins, J.; Lam, S.Y.; Skelly. J. P. Znt. J . Phurm. 1989,53,53-59. 4. Shah, V. P.; Elkins, J.; Hanus, J.; Noorizadeh, C.; Skelly, J. P. Pharm. Res. 1991,8, 55-59. 5. FDA contract with R. B. Stoughton, University of California at San Diego Medical School, La Jolla, CA. 6. FDA contract with Dr. Olsen, Duke University, Durham, NC. 7. Olsen, E. A. Arch. Dermutol. 1991,127,197-201. 8. Shah, V. P.; Peck, C. C.; Skelly, J. P. Arch. Dermutol. 1989,125, 1658-1561. 9. Caron, D.; Roueeel-Queille,C.; Shah, V. P.; Schaefer, H. J . Am. Acad. Dermatol. 1990,23, 45-62.
P. SHAH*', JEROME ELKINS*,
AND
JEROME P. SKELLY'
Received December 3,1990, from the 'Center for D N Evaluation ~ and Research, Food and DN Administration, Rockville, MD 20857, and Accepted for pu%cation March 13, 1991. 'Dallas District Laboratory, Food and Drug Administration, Dallas, TX 75204. Abstract 0 Betamethasone valerate creams from two firms were evaluated using the skin blanching procedure. In both studies, the same
cream formulation exhibited significantly higher blanching compared to the other product. An in vitro release rate was determined for these betamethasone valerate cream products using a diffusion cell system, with a cellulose acetate membrane and a 60% ethano1:water receptor medium. The release rate (flux) of betamethasone valerate was higher for the higher blanching formulation and was statistically different from the other product.The integrity of the cellulose acetate membrane in 60% ethanokwater mixture was ascertained using hydrocortisone cream product. The in vitro drug release method, using a diffusion cell system and a synthetic membrane, can serve as a good quality control test method for topical creams.
Glucocorticoids, when applied to the skin, exert a specific pharmacologicalresponse that is evident as skin blanching.l.2 This pharmaccdynamic response depends on the potency of the steroid and the drug release properties from the formulation, as well as the resultant pharmacokinetic behavior of the drug in the skin. For a topical cream product to be effective, it must first release the active drug from ita formulation. Measuring the drug release, therefore, may provide a useful and a meaningful method as a quality control test procedure. Shah et al. have developed a simple, reliable, and reproducible test procedure to study the release rate of hydrocortisone, a water-soluble drug, from the cream preparation.3.4 The method employs a diffusion cell system with commercially available synthetic membranes. This paper describes the application of the method to study the release profile of a poorly water soluble drug, betamethasone valerate, from a cream formulation. The release rates from the two brands of betamethasone valerate cream products were also compared with the pharmacodynamic properties of the drug.
Experimental Section Cream Products-Commercially marketed creams were used in this study. The betamethasone valerate creams were 0.1% valisone cream (Schering: lot nos. 6FE507 and 8FE300), and 0.1% betamethasone valerate cream (Fougera; lot nos. 6310 and 6520). The 2.5% hydrocortisone cream was from Dermik (lot no. 73411). Synthetic Membrane-The membrane was composed of mixed cellulose esters (cellulose acetate and nitrate), was 25 mm in diameter, 0.45 pm pore size, and 150 pm (6 mils) thick (Gelman Sciences Inc.) Diffusion Cells-" standard open-capped, ground-glass Franz diffusion cell, with a 15-mm diameter orifice (1.767 cm2 area, total diameter of cell = 25 mm), was utilized. The receptor phase was stirred by means of a constantly spinning bar magnet (Varispeed cell drive console, Crown Glaes Company). Receptor Phase-Different concentrations of an ethanokwater mixture, and pH 5.0 acetate buffer (0.05 M) were used. All receptor media were deaerated before use in the study. Sample Preparation-The synthetic membrane (25 mm in diameter) was soaked in the receptor phase and removed. A 2-mm thick x 104 / Journal of Pharmaceutical Sciences Vol. 81, No. 1, January 1992
the
17-mm diameter Teflon "mask, with a 15-mm hole in the center, was centered over the synthetic membrane. This 15-mm hole corresponded to the diameter and circumference of the membrane holder on the diffusion cell. The cream sample (-300 mg) was placed in the hole and spread uniformly with a Teflon squeegee by pulling across the Teflon mask. This procedure resulted in a smooth, even film of the sample, uniform in both thickness and diameter. The "mask was removed using tweezers and the prepared sample/membrane was transferred to the diffusion cell, with the cream side facing up.' Procedure-The lower part of the diffusion cell was filled with deaerated receptor phase medium. The synthetic membrane with the cream sample in the center and the top part of the cell were placed together and checked for air bubbles. If air bubbles were present, the sample preparation and procedure was repeated. If no air bubbles were present, the cells were clamped in place. Using a Microette automated sampler (Hanson Corporation, CAI interfaced with the diffusion cell, a 150-pL aliquot was withdrawn from the middle part of the cell at 30-, 60-, 120-, 240-, and 360-min intervals and analyzed by direct injection into a HPLC system. Aliquots of 150 pL were replaced &r each sample removal. The HPLC analysis of betamethasone valerate was carried out using a UBondapak C18 column (3.9 mm i.d., 30 cm long) and a 254-nm UV detector. Samples were eluted using an isocratic mobile phase consisting of acetonitri1e:water (60:40) at ambient temperature and a flow of 1.2 mumin. Under these conditions, the retention time for betamethasone valerate was 6 min, and detection limits were 8 ng per 2 0 - 4 injection, with a 5-108 CV. The concentration (pg/mL) of betamethasone valerate in the receptor phase was calculated using a standard of known concentration. The total amount of betamethasone valerate released (concentration in @mL x volume of the receptor phase) and the amount released per unit area (pg/cm2) were calculated. Skin Blanching Experiments-The Stoughton-McKenzie test1 for glucocorticoids was carried out in normal healthy volunteers by Stoughton6 and Olsens under two separate FDA contracts. The experimental details and results are published elsewhere.7
Results and Discussion The release rate of hydrocortisone from the cream was determined using aqueous media such as pH 5 acetate buffer, pH 7.4 phosphate buffer, and normal saline solutions. However, with betamethasone valerate cream, no drug could be detected in any of these receptor media up to 24 h. This is primarily because of low solubility (0.16 mg/100 mL) of betamethasone valerate in these receptor media. Addition of surfactants, such as sodium lauryl sulfate, Valpo, etc., also did not increase in vitro release. Use of 40% PEG 400 in water does increase the solubility, and small amounts of betamethasone valerate were detected in the receptor medium (5-14 &cm2 in a 6-h period). This quantity is too small to use as a quality control method and to detect any significant differences between the cream formulations. Therefore, other aqueous organic solventa were evaluated for use as receptor medium. The simplest aqueous organic solvents, such as methanol and ethanol in different concentrations, were tried. The synthetic membrane, cellulose acetate, was found to be unstable in 100% methanol; the membrane completely disThis article not subject to US.copyright. Published 1992, American Pharmaceutical Association
integrated. On the other hand, the membrane remained intact in ethanol (95%).Some cream formulations break down on coming in contact with 95%ethanol. Therefore, the release rate profile of betamethasone valerate was studied using 25, 50, and 60% ethanol. The results plotted against the square root of time are shown in Figure 1. The amount of drug released per unit area (pg/cm2)when plotted against square root of time ( t ) results in a straight line. The slope of the line
I
6o
/
50
I I
0
-
0
5 10 15 20 SQUARE ROOT OF TIME (MINUTES) flgure 1-In vitro release rate of betamethasone valerate cream in (0) 25, (*) 50, and (x) 6090 ethanol.
which represents the release rate (i.e., steady-state flux)was calculated using linear regression. As expected, because of higher solubility, the release rate was faster with a higher concentration of ethanol. It was decided to study the release of betamethasone valerate from all cream products using a 60% ethano1:water mixture. The integrity of the synthetic membrane, mixed celluose esters, in the presence of the 60% ethano1:water mixture was ascertained by using hydrocortisone cream product. The membrane was soaked in 60% ethano1:water for 16 h, air dried, and used to determine the hydrocortisone release from the cream. In another experiment, the membrane was used without soaking in 60% ethano1:water. The results of the study given in Table I show no statistically significant difference in release rate profile, thus establishing the integrity of the membrane when exposed to the 60% ethano1:water mixture. The in vitro release rate (flux)of betamethasone valerate, using the diffusion cell system, synthetic membrane, and 60% ethano1:water as the receptor medium, from the creams is shown in Table 11. The in vitro release data were plotted against the square root of time (t)and are shown in Figure 2. The difference in slopes (steady-state flux) between the two products relates to the differences in their relative ability to release the drug under the experimental conditions. The release rates of betamethasone valerate for the two products studied were significantly different from one another; the release rate was higher and faster for the brand name product (54-56 pglcm2) compared with the generic product (45-48 pglcm2) under the testing conditions. The difference in slope (release rate) is due to the difference between the formulation of the two products studied (Le., it may be due to the source of the active ingredient or the raw materials in the vehicle phase of each cream). Even if the vehicle composition (ingredients, percentages, etc.) may be the same in each cream, the differencescould be related to the sources of raw materials or manufacturing process. The drug solubility, initial drug concentration, diffusion constant of the drug in the vehicle, and other formulation adjuvants play a
Table H n Vltro Release of Hydrocortisone from Cream'
Hydrocortisone Released, pgIcmzb
Membrane Membrane NOTsoaked in 60% ethanol Membrane soaked in 60% ethanol and dried t statisticd
Flux'
Regression Correlation Coeff lcient
30 min
60 min
120 min
240 min
360 min
20.7 (9.1) . .
40.0 (11.1)
71.8 (3.)
133.1 (3.5)
188.8 (3.1)
12.5
0.988
21.3 (3.7)
41.3
74.4 (3.1)
133.1 (3.4)
191.2 (4.3)
12.6
0.988
-
-
0.77
0.68
(2.8)
1.97
0.93
0.58
* Hydrocortisonecream (2.5%. Dermik X7341 l), diffusion cell, cellulose acetate membrane, and pH 5.0 acetate buffer. Data within parentheses represent percent coefficient of variation (n = 6). Flux = slope = pg/cm2/min0'. No difference at any time point. Table l C l n Vltro Release of Betamethasone Valerate from Creams'
Product Study I
Schering 6FE507 Fougera 6310 t statistic' Study II
Schering 8FE 300
Fougera 6520 t statisticd
Betamethasone Valerate Released, pglcm2 120 min 240 min
30 min
60 min
5.9 4.7 2.25
11.7 9.7 2.56
22.8 20.2 2.09
40.2 35.8 2.92
4.8 4.3
12.1 9.0 2.46
23.0 18.7 3.36
40.5 33.1 4.66
0.83
360 min
54.0 48.2 3.10 55.5
44.3 4.71
a Using diffusion cell, cellulose acetate membrane, and 60% ethanokwater as the receptor medium. Flux different at all time points. Significantly different at all time points except 30 min.
= slope =
Fluxb
Regression Coefficient
3.56 3.19
0.996 0.997
3.78 2.96
0.997 0.997
-
-
pg/cm2/min0'. Significantly
Journal of Pharmaceutical Sciences I 105 Vol. 81, No. 1, January 1992
Table IlCSummary of the In Vlvo Blanchlng Score for Betamethasone Vakrate Cream6 study
Number SubjectsOf
Product
I
30
II
32
Schering Fougera Schering Schering Fougera Fougera
Number
..
5 10 15 SQUARE ROOT OF TIME (MINUTES)
20
Flgure 2-In vitro release rate of two betamethasone valerate creams in 60% ethanol. Key: (*) Schering; (0)Fougera.
- 7 -R ?
3 56
2 33
SCHERING
PD
T FOUGE
IN VlTRO
PD
IN VlTRO
STUDY I
STUDY 11 Flgure 3-Correlation between pharmacodynamicresponse and in vitro release rate in 60% ethanokwater for betamethasone valerate creams. major role in affecting the drug release rate. In addition, the release rate of the drug from the cream formulation largely depends on the same manufacturing variables which influence the quality and efficacy of the preparation. Because of these reasons, the release rate can be used as a quality control measure to assure batch-to-batch uniformity. The release rates of betamethasone valerate from two batches from the same manufacturer were not significantly different (t statistics), again suggesting that the procedure can be used as a quality control method for assuring batchto-batch uniformity. For topical glucocorticoids, the “vasoconstriction” or, correctly designated, “skin blanching” test is canied out to determine the potency and bioequivalence of the product.8 In 106 I Journal of Pharmaceutical Sciences Vol. 81, No. 1, January 1992
Total Score
Average Score
70 49 72 73
2.33 1.63 2.25 2.28 1.94 2.09
62 67
two such independent studies (referred to as Study I and Study II), the skin blanching score of the brand name product was compared with a generic praduct.6.6 In study 11, the same two products were administered twice.6 Table I1 provides a summary of both in vivo study results. The total skin blanching score is a n indicator of relative response of the product. The ANOVA indicated that the difference in response between the two betamethasone valerate creams was highly significant, in both studies. Figure 3 compares the in vitro release rate of betamethasone valerate with the in vivo blanching score. The rank-order release rate obtained correlated with the blanching score of the products in both of the studies, thus adding validity to the in vitro method. The rank-ordered correlation of pharmacodynamic data (skin blanching score)with the in vitro release rate (pg/cm2/h) adds validity to the newly developed in vitro quality control test. A similar rank-order correlation was observed for hydrocortisone creams with pharmacokinetic (concentrations of drug in skin), pharmacodynamic (skin blanching score), and in vitro release rate (flux,c~@/mL/h) data.9 In spite of having a good in vitro:in vivo rank-order correlation in the case of betamethasone valerate cream and hydrocortisone cream products studied, it should be emphasized that the in vitro release test described is strictly a quality control test to assure lot-to-lot uniformity, and it should not be used to predict bioactivity. The correlation obtained between the in vitro release and in vivo performance adds strength and validity to the in vitro test. In conclusion, a simple, reliable, and reproducible method using a commercially available synthetic membrane and diffusion cell assembly has been developed and established to measure the release rate of drug, such as hydrocortisone and betamethasone valerate, from cream formulations. The validity of the method has been evaluated and confirmed. The method can be used as a quality control test to assure lot-to-lot uniformity of the product. The in vivo drug penetration and absorption process is very complex, whereas the in vitro test procedure is highly simplified. Therefore, extrapolation of the data (results) should be carried out with caution.
References and Notes 1. McKetlzie, A. W.; Stoughton, R. B. Arch. Dermatol. 1962, 86, 608410. 2. Cornell, R.C.; Stoughton, R.B. Arch. Dermatol. 1985, 121, 63-67. 3. Shah, V. P.; Elkins, J.; Lam, S.Y.; Skelly. J. P. Znt. J . Phurm. 1989,53,53-59. 4. Shah, V. P.; Elkins, J.; Hanus, J.; Noorizadeh, C.; Skelly, J. P. Pharm. Res. 1991,8, 55-59. 5. FDA contract with R. B. Stoughton, University of California at San Diego Medical School, La Jolla, CA. 6. FDA contract with Dr. Olsen, Duke University, Durham, NC. 7. Olsen, E. A. Arch. Dermutol. 1991,127,197-201. 8. Shah, V. P.; Peck, C. C.; Skelly, J. P. Arch. Dermutol. 1989,125, 1658-1561. 9. Caron, D.; Roueeel-Queille,C.; Shah, V. P.; Schaefer, H. J . Am. Acad. Dermatol. 1990,23, 45-62.