AUEC at D, = 0.5 [AUEC at D, (left arm) + AUEC at 0,
{right arm)].

Only those subjects with a complete data set, i.e., duplicate
values of D, and D,, and quadruplicate values of T, R, and UNT,
should be included in the data analysis.

The bioequivalence comparison should be based on AUEC values
computed according to Section V(H)(1)(b) at the dose duration

corresponding approximately to EDs. [treatments T and R,
Section V(G)(2)].

All study data, including the data of ‘nondetectors,’ should be
submitted. An explanation (e.g., ‘nondetector,’ overlap of
vasoconstrictor effect due to an adjacent site, etc.) should
accompany any data not used in the bioequivalence evaluation.

2. Statistical Analysis

a.

The statistical analysis requires the use of untransformed data
because AUEC values of treatments T and R, calculated from
baseline-adjusted, untreated control site-corrected data, although
generally negative, are sometimes positive. The presence of
both positive and negative data eliminates the use of
conventional statistical transformations. Previously used
approximate methods,'* for example calculating a confidence
interval for the difference between test and reference product
averages, and dividing these limits by an estimate of the
reference product average, are not applicable. Locke’s
method'* provides an exact confidence interval from
untransformed data.

The 90% confidence interval should be calculated for the ratio of
the average AUEC response due to the test product (average of
four replicates) to the average AUEC response due to the
reference product (average of four replicates) using Locke’s
method. The formulae and a worked example, based on the data
of Table AIV.6, are given in Appendix V.

The Office of Generic Drugs has not determined at this time the
equivalence interval for bioequivalence. The Office recognizes
that an equivalence interval wider than 80-125%, as a public

standard, may be necessary pending evaluation of data
submitted to the agency.

The randomization code, indicating the specific skin sites to
which each dose duration and control site was assigned, should
be submitted with the study report.

19


Table AIV.6 AUEC,..,, data for right and left arms, the two arm average data for test and
reference products of all 12 subjects at a dose duration of 2.0 hours

AUECo.24, of TEST PRODUCT AVEC .24, of REFERENCE PRODUCT
SUB ARM LOC AUEC AUEC* SUB ARM LOC AUEC AUEC*
(AVERAGE) (AVERAGE)
1 R 3 -16.20 -21.69 1 R 4 -27.29 -43.03
en -27.19 1 Lb 4 -68.77
2 bt 3 -56.98 2 RR 4 ~— -28.65
2 R414 -40.06 2 bo 4-15.75
3 Lt 3 -43.63 3° R14 “15.27
3 R 2 -34.36 3 L 4 — -22.03
4 R14 -14.06 4 R 4 — -26.67
4 Lt 3 “1.18 4  L 2 -18.18
5 L 3 -8.39 -13.34 5 LL 2 -36.48. -34.25
5 R 1 -18.29 5 R 3-33.01
6 R 4 -9.51 “15.23 6 R 1 0.01 -18.83
6 L 3 -20.96 6 L 4 — -37.68
7 R 4 -12.05 0.98 7 R 2 -12.17
7 bo 1 14.01 7 Lb 4 -9.75
8 R 4 0.30 0.56 8 R 2 13.87 -7.94
8 Lt 3 0.81 8 L 1-29.45
9 R 1 -43.68 9 R 4 -41.15
9 t 3 -20.42 9 LL 2 -33.65
10 R 14 -10.61 “11.51 10 Lb 3 -20.35 -16.10
10 Lt 3 “12.41 10 R 1 -11.86
47 Lb 2 -26.33 cn -26.13
1 oR 3 -26.04 170 Lb 4 -27.33
12 L 3 -15.77 12, R 1 -35.19
12, oR 3 “7.47 12 Lb 4 10.08
MEAN “18.77 “18.77 -22.59 -22.59
sD 16.45 15.28 16.14 10.92
SE 3.36 3.12 3.30 2.23
%CV 88 81 1 48

*Highlighted cells show AUEC data of seven subjects whose AUEC ratios (see Table AIV.5) were = 1.25,
i,e., evaluable subjects. These AUEC data were used in the calculation of the 90% confidence interval
in Appendix V.

34


Note: Optimal assessment times for either method of application and

removal may require adjustment of these schedules for the
particular drug product and study site. For either method, at
least one reading should be scheduled between 5 PM and
midnight.

J. Data Analyses and Pharmacodynamic Modeling
1. Chromameter Data
a.

Adjust the chromameter raw data of each skin blanching
response versus time profile (both active drug sites and untreated
control sites) for the baseline value at that site. Correct each
baseline-adjusted active drug site for the mean of the two
baseline-adjusted untreated control sites on the same arm (Tables
Alll.1 - Alll.3).

Using the trapezoidal rule, compute the area under the effect
curve (AUEC) for each baseline-adjusted, untreated control site-
corrected dose duration (Tables Alll.3, Alll.4):

i. AUEC 9.24, for the staggered application with synchronized
removal method, or

ii. AUEC..29) for the synchronized application with staggered
removal method [based on the dose duration schedule of
Section IV(I)(6)]._ In the general case, AUEC from the
longest dose duration to 28 hours after drug product
application is computed.

Fitting dose duration-response data by averaging across subjects
at each dose duration is not acceptable. Rather, the data should
be fit by using all observations of all individual subjects
simultaneously. The modeling software should provide EDso and
Enax Values for the data pooled from 12 subjects. The following
methods are acceptable:

i. Fitting based on the assumption of a nonlinear mixed
effect model (population model) using suitable software
(Figure Alll.1). The mixed effect modeling technique
accounts for within- and among-subject variability, or

ii. Fitting based on nonlinear least squares regression,

pooling individual observations from ail subjects (naive
pooled data method).

13




In considering the following sections, the reader may find it useful to compare
assay validation for a standard HPLC or GLC assay with validation for the
vasoconstrictor bioassay. The latter method substitutes an observed
pharmacodynamic response to an amount of drug, in this instance the
vasoconstrictor response to a topical corticosteroid, for the detector response
of an HPLC or GLC to a known amount of drug. Whereas only one instrument
and detector are used in a standard blood or urine level assay, each subject in
a pharmacodynamic bioassay study becomes the “detector’ responding to a
known or unknown amount of drug. Despite many fundamental differences
between a standard blood or urine level assay and a bioassay, many of the
principles regarding standardization and validation are comparable. Several of
these issues are discussed in the following sections.

1, Linearity

Understanding of basic pharmacodynamic relationships between either
dose or concentration and a. pharmacodynamic response of interest has
expanded considerably over the last 15 years.® Application of this
knowledge to the vasoconstrictor bioassay relates to an assessment of
linearity. Although various models are available to express a relationship
between drug dose and effect, one that may be especially useful to the
vasoconstrictor bioassay is the E,,, model, or the related sigmoid E,.,.
model, which describes some measure of effect (£) in terms of a
baseline effect (E,), a maximal effect (E,..) and a dose (D) at which the
effect is half-maximal (ED,,):

Enax x D

E = +
Fo ED, + D

The in vivo vasoconstrictor response generally approaches a maximum.
Therefore, a primary issue requiring resolution in the application of the
vasoconstrictor assay to assess bioequivalence is whether, at the
strengths of the formulations to be tested in the assay, the capacity of
the microvasculature of the skin to respond linearly has been exceeded.
At relatively high strengths of a topical corticosteroid, minimal change
in the vasoconstrictor response may occur, irrespective of increments
in dose duration. At relatively low strengths of a topical corticosteroid,
the question becomes one of determining the minimal dose that will
produce a reliable and reproducible vasoconstrictor response. These
questions are analogous to those confronted in the validation of an
assay for drug levels in blood or urine, namely, to define the standard
curve of an assay and the lower limit of sensitivity. Development and
validation of a dose-response standard curve is essential to estimation
of EDso, D, and D,.


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Computer Formatted Data Submission

A diskette in the ASCII format containing the study data should be
submitted with the application. Chromarneter raw data; baseline-
adjusted data; baseline-adjusted, untreated control site-corrected data;
and AUEC data should be arranged in separate files in the format given
in Tables AIV.1 - AIV.6.

20


APPENDIX |

STAGGERED APPLICATION WITH SYNCHRONIZED REMOVAL:
SCHEMATIC FOR A SUGGESTED PILOT STUDY PROTOCOL

Figure AL1

Baseline (BL) Measurement, Drug Application and Drug Removal

|
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if =e
£} vpteaton rine t i
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f=

ol

T
6 5 4 3 2 4

Hours Before Drug Removal

Figure Al.2

Skin Blanching Measurements

t Removal Time

J Measurement Time

tt Hours After Drug Removal

24





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A representative application sequence for a particular subject might be:

ANTECUBITAL FOSSA

Left Arm Right Arm

D, dD,
T R

UNT UNT
R T

UNT UNT
T R
D, D,

a
WRIST

The specific pattern of skin sites, i.e., medial (ulnar) to lateral (radial),
and superior to inferior, should be described by the firm.

Either the staggered application with synchronized removal or the
synchronized application with staggered removal method, consistent

with the methodology used in the pilot study, should be used for D,, D2,
and EDc¢, dose durations.

Examples of time periods for assessment of baseline skin color and skin
blanching at each site are:

a. For staggered application with synchronized removal:
For all dose durations and untreated control sites, baseline
readings within one hour prior to drug application of the longest
dose duration; skin blanching readings at O, 2, 4, 6, 19, and 24
hours after drug product removal. Actual times will depend upon
the time of dosing and the topical corticosteroid being studied.
Time zero equals time of drug product removal.

b. For synchronized application with staggered removal:
For all dose durations and untreated control sites, baseline

readings within one hour prior to the time of drug application to
active drug sites; skin blanching readings at the following times

7


No bathing or showering during the periods of drug application and
assessment of skin blanching.

No use of creams, emollients, or similar products to forearms for 24
hours prior to and throughout the study.

Subject Screening for Response

1,

Inclusion of ‘nonresponders’ reduces the ability of a study to detect true
differences between test and reference products, should they exist.
Therefore, for both the pilot dose duration-response study and the
pivotal bioequivalence study, only ‘responders,’ i.e., subjects who have
the capacity to vasoconstrict when dosed with the RLD used in the
study, should be included.

In this Guidance, a ‘responder’ is defined as a subject who shows a
response to a single dose duration of the RLD under the same occlusion
or nonocclusion conditions used in the pilot and pivotal studies.
Quantification of skin blanching in the pilot and pivotal studies by the
chromameter is considered to be the most satisfactory. However,
because of the discrete multiple unit scale (0 - 3 or O - 4) for visual
readings, ‘responder’ status may be based on visual readings. A dose
duration of 4 hours (based on a potency group II! product,* with the
results shown in Figure Alll.1), or 6 hours'' is suggested, with skin
blanching assessment 2 hours following drug product removal. A
‘responder’ shows a visual reading of at least one unit.

To conserve skin sites on the forearm for use in the dose duration-
response study or bioequivalence study, ‘responder’ status may be
based on studies conducted at sites other than the forearm.

Criteria for identification of responders, including dose duration,
magnitude of response, and skin site tested, should be included in the
study report. Responder status may also be documented from
participation in a previous vasoconstrictor assay study.

Validation of Assay Precision

Validation of intraspot and interspot precision of the assay methodology should
be documented in four to six subjects who meet the criteria and restrictions of
Sections IV(B - D). Four untreated control sites on each ventral forearm should
be selected. Four chromameter readings of each site should be made within a
one hour period.

The validation study documents acceptable precision by the bioequivalence
testing firm in utilizing the chromameter for the measurement of skin blanching.
The study should be conducted prior to administration of the drug product.


APPENDIX IV

ANALYSIS OF DATA FROM AN AGENCY-SPONSORED ‘PIVOTAL’ STUDY:
AN EXAMPLE

Appendix !V presents chromameter a-scale data and AUEC,..2., data of the University of
California ‘pivotal’ in vivo bioequivalence study referred to in Appendix Ill. In the ‘pivotal’
study, the bioequivalence comparison is based on the dose duration-response analysis
summarized in Figure Alll.1, Note 3. Table AlV.1 presents the a-scale raw data through 24
hours for subject 1. Baseline-adjusted data are presented in Table AlV.2, and baseline-
adjusted, untreated control site-corrected data are presented in Table AlV.3. In this example
data set, each active drug site was corrected for its corresponding untreated control site.
However, the guidance recommends use of only two untreated control sites per arm, and
subtracting their average from all active drug sites on that arm. Table AlV.4 presents the
baseline-adjusted and untreated control site-corrected a-scale data for test and reference
products for all subjects. Table AlV.5 presents right and left arm AUEC,24 data, and the two
arm average data, for D, and D, for all subjects. Table AlV.5 also identifies ‘detectors,’ i.e.,
evaluable subjects, defined as those subjects who met the dose duration-response criterion
{Section V(H)(1}{c)]. Table AIV.6 presents right and left arm AUEC,.24 data, and the two arm
average data, for test and reference products for all subjects at a dose duration of 2.0 hours,
and highlights the two arm average AUEC,.4, data of the ‘detectors.’ Only the data of
‘detectors’ are included in the analysis for bioequivalence, as described in Appendix V.

Table AIV.1 Chroma Meter (Minolta) a-scale raw data for a subject

SUB TRT ARM LOC SITE BL Hours after drug removal
te) 2 4 6 19 24

UNT 7.34 7.23 8.09 7.64 7.82 7.68 8.71
TRT 7.11 7.86 7.59 5.92 6.23 6.32 7.30
UNT 6.18 7.38 7.26 6.85 7.35 7.14 7.87
TRT 6.79 6.29 6.12 4.45 5.88 6.01 7.26
UNT 6.28 7.32 7.80 6.77 7.75 6.59 7.55
TRT 7.78 9.26 9.30 7.42 8.24 7.40 8.59
UNT 9.31 10.19 10.61 9.56 10.88 9.52 10.13
TRT 7.38 8.22 6.94 5.07 6.98 7.24 7.91
UNT 7.62 7.98 7.56 7.48 7.24 6.73 7.49
TRT 6.97 5.42 5.39 4.39 4.79 5.76 6.45
UNT 7.12 6.32 6.76 6.25 6.74 6.80 7.58
TRT 7.46 4.48 4.38 4.11 4.39 6.27 7.25
UNT 7.69 7.03 7.73 7.21 7.87 7.89 8.38
TRT 8.99 8.75 8.07 6.74 6.53 7.14 8.25
UNT 8.99 8.28 8.95 8.50 9.10 9.05 9.93
TRT 8.80 8.04 6.71 5.51 5.14 7.05 7.96

Boe enn enn n nnn
oUrPraDNNDTDIONNABHMYS yD
rerrerrer eo oan nnwaTD
PAKWWNHNABAARWWNN AA

TRT A: RLD at dose duration D, (1.0 hour)

TRT B: RLD at dose duration D, (4.0 hours)

TRT C: Test drug product at dose duration of 2.0 hours

TRT D: RLD at dose duration of 2.0 hours

UNT: Untreated control site (no product applied) corresponding to each treated site

30


Table Alll.2 Baseline-adjusted a-scale data for a subject

SUB OD SITE

eee enn nnn nnn inn

0.25
0.25
0.5
0.5
0.75
0.75

ODO PPANN,

UNT
TRT
UNT
TRT
UNT
TRT
UNT
TRT
UNT
TRT
UNT
TRT
UNT
TRT
UNT
TRT

BL

Hours after drug removal

0
0.13
~0.47
-1.07
-0.82
0.30
0.20
0.63
0.28
-0.05
0.01
0.01
-0.03
-0.88
0.07
0.28
0.24

2

0.24
0.02
0.51

-0.24
-0.21
0.07
-0.55
0.35

0.02

0.40
-0.62
0.40
-0.11
0.15

-0.39
-0.07

4
-0.34
-0.04
-0.73
-0.32
-0.29
-0.42
-0.97
0.01
-0.17
0.34
-0.19
-0.13
0.00
-0.23
-1.15
-0.45

6

0.17
0.15
0.34
-0.81
0.47
-0.20
-0.06
-0.47
0.48
-0.41
-0.73
0.03
0.87
-0.25
0.11

0.17

19
0.54
0.50
0.60
0,81
-0.02
0.26
0.33
0.14
0.15
0.64
0.83
1.18

~0.41
~0.06
0.93
0.79

24
-0.21
-0.32
0.32
0.23
-0.23,
0.10
0.66
-0.31
-0.43
-0.35
0.72
-1.36
0.29"
0.09
0.33
0.26

Table Alll.3 Baseline-adjusted,
data for a subject

untreated control site-corrected

a-scale data and AUECo24,

SUB DD SITE BL Hours after drug removal AUECo.24*
Oo 2 4 6 19 24
1 0.25 TRT - -0.60 -0.22 0.30 -0.02 -0.04 -0.11 -1.23
1 0.5 TRT - 0.25 -0.75 0.41 -1.15 0.21 -0.09 -7.39
1 0.75 TRT - -0.10 0.28 -0.13 -0.67 0.28 0.33 -1.48
1 1 TRT - -0.35 0.90 0.98 -0.41 -0.19 -0.97 -3.80
1 1.5 TRT - 0.06 0.38 0.51 -0.89 0.49 0.08 -0.23
1 2  =TRT - -0.04 1.02 0.06 0.76 0.35 -2.08 5.77
1 4 TRT - 0.95 0.26 -0.23 -1.12 0.35 -0.20 -4.74
1 6 TRT - -0.04 0.32 0.70 -0.28 -0.14 -0.07 -1.53

* AUEC 24, units are baseline-adjusted, untreated control site-corrected a-scale units times

hours

27


Minolta) to detect erythema offers the possibility of replacing subjective visual
scoring in the vasoconstrictor assay with objective, quantifiable
measurements.”® The Division of Bioequivalence currently considers the use
of a chromameter to be applicable to bioequivalence studies based on the
vasoconstrictor assay, and therefore recommends that pharmaceutical sponsors
incorporate the use of a chromameter into their study designs. However, with
acceptable validation, which includes establishing the correlation between
chromameter measurements and visual estimation data, sponsors may rely on
visual estimation of the degree of vasoconstriction.

Some Conclusions from Agency-Sponsored Studies

Results of vasoconstrictor assays conducted under agency contract have led
OGD to conclude the following:

1. The chromameter possesses greater sensitivity to skin blanching than
does visual estimation,

2. Skin blanching response measured over two consecutive 24 hour
periods (48 hours) appears to follow a circadian pattern, possibly the .
result of a circadian pattern in plasma cortisol fevels.*'° AUEC data
through at least 24 hours from time of drug product removal or drug
product application [Section IV(I)(9)], appear acceptable for
bioequivalence comparisons, and

3. For baseline-adjusted, untreated control site-corrected AUEC data based

on chromameter measurements, these studies suggest there is no strong
indication of:

a. a difference in response between left and right arms, or

b. a location effect on the arm when skin sites are no closer than
3 - 4 cm to the antecubital fossa or to the wrist.

Using the experimental design recommended in Section V(G)(2), in
which the application pattern on each arm is complementary, e.g., T is

complementary to R, the impact of such effects, should they occur, is
minimized.

PILOT DOSE DURATION-RESPONSE STUDY

The purpose of the pilot study is to determine the dose duration-response relationship
of the topical corticosteroid to be studied in the pivotal in vivo bioequivalence study.
The study is analogous to developing a standard curve in the assay of a drug in a
biologic fluid matrix. The outcome of the pilot study provides the dose duration-
response information necessary to determine the parameters EDso, D,, and D, to be
used in the firm’s pivotal in vivo bioequivalence study, and an estimation of the

6


In standard analytical methods validation, establishing linearity in
detector response is necessary. Linearity in response is also desirable
in the development of a vasoconstrictor assay. Because the intended
generic and reference commercial formulations may be marketed at
strengths that produce responses on the flat portion of the dose-
response curve, the assay must be optimized to assure that the products
are compared in the linear portion of the curve. Development of a dose-
response relationship for a topical corticosteroid relies on some reliable
way to administer a predetermined dose of the drug product to the skin.
In the Interim Guidance,’ three methods were postulated to be
acceptable ways of reliably delivering a dose of topical corticosteroid:
1) the dose duration method; 2) the dilution method; and 3) the area
method. Both the dose duration method and the dilution method
showed promising results in agency sponsored studies.© From a
formulation viewpoint, the dilution method is impractical, thus CDER
scientists believe that the dose duration method is the most suitable for
documentation of bioequivalence of topical corticosteroids.
Development of a dose duration-response relationship for a topical
corticosteroid will indicate points in the effect-time relationship at which
the vasoconstrictor response becomes insensitive. in principle, the time
course of response should be followed to return to baseline to insure
that at each dose duration, the maximal pharmacodynamic response is
observed.

2. | Accuracy, Precision and Sensitivity

Development of methodology to establish the accuracy, precision, and
sensitivity of a bioassay for a topical corticosteroid should be coincident
with the development of an acceptable standard curve for the
vasoconstrictor assay. This information, as well as the standard curve,
should be developed for each study population. As with a standard
blood or urine assay, this information will be developed through the use
of untreated controls and calibrators containing the topical corticosteroid
of interest. Replication of the untreated controls and calibrators will
allow estimation of coefficients of variation. Just as a calibrator in a
standard HPLC or GLC assay involves measurement of the detector
response to a known concentration of drug substance, the calibrator for
a pharmacodynamic topical corticosteroid bioassay, based on the dose
duration method, involves application of a standard strength of a topical
corticosteroid product for different periods of time.

Measurement of Vasoconstrictor Response

In an era with increasingly sophisticated methods to detect changes in light,
temperature, pressure, and other physical and chemical changes, the use of a
human observer to assess the magnitude of a pharmacodynamic effect
becomes increasingly inadequate. Application of a commercially available
chromameter (or colorimeter; e.g., Chroma Meter 200 or 300 model series,


after drug product application: D, (see Note below), 6, 8, 11, 24,
and 28 hours. Actual times will depend upon the time of dosing,
the topical corticosteroid being studied, and D,.

Time zero equals time of drug product application.

Note: For example, if D, for a specific drug product equals 4
hours, the first post-baseline reading of all skin sites, both
active drug sites and untreated control sites, would be at
4 hours. For either method, at least one reading should
be scheduled between 5 PM and midnight.

H. Data and Statistical Analyses
1. Data Analysis
a. For the chromameter raw data, adjust each skin blanching

response versus time profile (both active drug sites and untreated
control sites) for the baseline value at that site. Correct the data
of each baseline-adjusted active drug site for the mean of the
two baseline-adjusted untreated control sites from the same arm
(Tables AIV.1 - AIV.4).

Compute AUEC for each baseline-adjusted, untreated control
site-corrected dose duration (Tables AIV.3, AIV.5, AlV.6).

i. AUEC,o.24 for the staggered application with synchronized
removal method, or

ii. AUEC from time D, to 28 hours, AUECio225, for the
synchronized application with staggered removal method.

Only the data of ‘detectors,’ i.e., individual subjects whose
AUEC values (Table AIV.5) at D, and D, are both negative and
that meet the dose duration-response criterion below, should be
included in the data analysis (Tables AIV.6, AV.1). The dose
duration-response criterion is:

AUEC at D,

an 2s 1.25
AUEC at D,

where:

AUEC at D, = 0.5 [AUEC at D, (left arm) + AUEC at D,
{right arm)];

18


Subject Inclusion Criteria

1.

2.

3.

4.

Healthy subjects.

Subjects demonstrating adequate vasoconstriction to topical
corticosteroids, i.e., ‘responders’ [Section IV(E)].

Written informed consent.

Willingness to follow study restrictions.

Subject Exclusion Criteria

1.

2.

10.

Clinically significant hypertension or circulatory disease.
Individuals smoking within one week of study.

Caffeine intake greater than 500 mg per day prior to or during the study.
(A cup of coffee contains about 85 mg of caffeine).

Clinically significant history of alcoholism or drug abuse.

Use of topical dermatologic drug therapy on ventral forearms, including
prior dosing of a topical corticosteroid in a pharmacodynamic study to
a particular skin site, within one month prior to the study.

Adverse reactions to topical or systemic corticosteroids.

Any current or past medical condition, including active dermatitis or any
other dermatologic condition, which might significantly affect
pharmacodynamic response to the administered drug.

Persons who would require shaving ventral forearms to insure consistent
dose on skin surface.

Use of any vasoactive (constrictor or dilator) medication, prescription or
OTC, that could modulate blood flow. Examples of such drugs include
nitroglycerin, antihypertensives, antihistamines, NSAID’s, aspirin, and
OTC cough/cold products containing antihistamines and/or either
phenypropanolamine or phentolamine.

Any obvious difference in skin color between arms.

Study Restrictions

1.

No exercise with either arm, and no strenuous exercise overall, for study
duration.


10.

11.

12.

REFERENCES

Shah VP. Interim guidance, topical corticosteroids: in vivo bioequivalence and in vitro
release methods. Division of Bioequivalence and Division of Anti-Infective Drug
Products, Center for Drug Evaluation and Research, Food and Drug Administration,
Rockville, MD: 1 July 1992.

Pershing LK, Silver BS, Krueger GG, Shah VP, Skelley [sic] JP. Feasibility of measuring
the bioavailability of topical betamethasone dipropionate in commercial formulations
using drug content in skin and a skin blanching bioassay. Pharm Res 1992;9:45-51.

Stoughton RB. Vasoconstrictor assay - specific applications. In: Maibach HI, Surber C,
eds. Topical corticosteroids. Basel: Karger, 1992:42-53.

Shah VP, Midha KK, Dighe S, et al. Conference report. Analytical methods validation:

bioavailability, bioequivalence and pharmacokinetic studies. Pharm Res 1992;9:588-
92.

Holford NHG, Sheiner LB. Understanding the dose-effect relationship: ctinical

application of pharmacokinetic-pharmacodynamic models. Clin Pharmacokin 1981;
6:429-53.

Pershing LK, Lambert L, Wright ED, Shah VP, Williams RL. Topical 0.050%
betamethasone dipropionate: pharmacokinetic and pharmacodynamic dose-response
studies in humans. Arch Dermatol 1994;130:740-7.

Queille-Roussel C, Poncet M, Schaefer H. Quantification of skin-colour changes
induced by topical corticosteroid preparations using the Minolta Chroma Meter. Br J
Dermatol 1991;124:264-70.

Elsner P. Chromametry: hardware, measuring principles, and standardization of
measurements. In: Berardesca E, Elsner P, Maibach HI, eds. Bioengineering of the skin:
cutaneous blood flow and erythema. Boca Raton: CRC Press, 1995:247-52.

Krieger DT, Allen W, Rizzo F, Krieger HP. Characterization of the normal temporal
pattern of plasma corticosteroid levels. J Clin Endocrinol Metab 1971;32:266-84.

Pershing LK, Corlett JL, Lambert LD, Poncelet. Circadian activity of topical 0.05%
betamethasone dipropionate in human skin in vivo. J Invest Dermatol 1994;102:734-9.

Smith EW, Meyer E, Haigh JM, Maibach HI. The human skin blanching assay as an
indicator of topical corticosteroid bioavailability and potency: an update. In Bronaugh
RL, Maibach HI, eds. Percutaneous absorption: mechanisms-methodology-drug
delivery. 2nd ed. New York: Marcel Dekker, 1989:443-60.

Singh GJP, Lesko LJ, Shah VP, et al. Bioequivalence methodology for dermatologic

corticosteroids based on pharmacodynamic modeling [Abstract]. Clin Pharmacol Ther
1995;57:181.

22


CENTER For Druc EVALUATION AND RESEARCH

Guidance for Industry

The FDA published Good Guidance Practices in February 1997.
This guidance was developed and issued prior to that date.

Additional copies are available from:
Office of Training and Communications
Division of Communications Management
Drug Information Branch, HFD-210
5600 Fishers Lane
Rockville, MD 20857

(Tel) 301-827-4573
(Internet) http://www.fda. gov/cder/guidance/index.htm

U.S. Department or HEALTH AND HuMAN SERVICES, Foop AND DruG ADMINISTRATION



performed not less than two hours prior to drug product application. If
cleansing is performed, this should noted in the study report.

Whether the study is conducted under occlusion or nonocclusion
conditions, use of a protective, nonocclusive guard to prevent smearing
or removal of topical drug product from the skin site. Care should be
taken to avoid contact between the guard and any drug product to
prevent inadvertent contamination of untreated control sites or other
test sites.

Skin sites should be no closer than 3 - 4 cm to the antecubital fossa or
to the wrist.

Application of the RLD to skin sites of identical surface area on the
ventral forearms. Suggested dose durations for the pilot study are 0.25,
0.5, 0.75, 1, 1.5, 2, 4 and 6 hours, but may vary depending on the
corticosteroid under investigation.

a. Eight dose durations, i.e., active drug sites, should be equally
divided between the two arms.

b. Amount of drug product, skin site size, and spacing between
sites should be determined by the testing laboratory. For
reference, some investigators have used doses of 2 - 10 mg of
formulation per cm? of skin surface area, and 1 cm diameter
sites. Sites may be spaced as close as 2.5 cm center-to-center,
and may be in a straight line or staggered pattern, depending on
skin surface suitability (e.g., vascularity, nevi, etc.) and arm
length. lf vasoconstrictor effects of two adjacent test sites
overlap and the investigator cannot discern between the
vasoconstrictor effect at each test site, the subject should be
excluded from the data analysis.

Use of two untreated control skin sites per arm for studies based on
chromameter measurements.

a. Application to each subject of eight dose durations [Section
IV(I)(6)] and four untreated control sites should be randomly
assigned among the 12 sites, maintaining two untreated control
sites and four dosed sites on each arm (six sites per arm).

b. Studies based on visual scoring do not require untreated control
sites because the reading involves a visual comparison of the
treated site to the surrounding skin. Application to each subject
of eight dose durations should be randomly assigned between
the two arms, maintaining four dosed sites on each arm.


Results should be provided in the pilot study report, if submitted [Section
IV)(J)(3)], and in the pivotal in vivo bioequivalence study report.

Occlusion versus Nonocclusion

Class labeling for topical corticosteroids states that occlusive film may be used
for the management of psoriasis or recalcitrant conditions. This statement may
be found in labeling of certain products representing all potency groups,
although labeling for certain high potency products specifically states that
occlusive films are not to be used. Provided occlusion is allowed in the labeling
of the specific reference listed drug, the pilot dose duration-response study and
pivotal in vivo bioequivalence study may be conducted using occlusive film.
However, caution must be used, as analyses of pilot studies conducted under
agency contract suggest that the ED, (the dose duration to be used in the
pivotal study) decreases with increasing topical corticosteroid product
potency.'? Evaluation of dose duration-response requires dose duration data
at times less than the EDco. Very short dose durations are difficult to conduct
experimentally and tend to produce high variability in response. Thus occlusion
may be appropriate only for the lower potency products, e.g., potency groups
Vi and Vil. If occlusion is used for the pilot study, it should also be used for
the pivotal study.

Methods of Application and Removal

Either of two methods of application and removal may be utilized in the pilot
and pivotal studies [Section V(G)(3)]:

1. Staggered application with synchronized removal, in which drug is
applied to skin sites at different times and removed at the same time
(Appendix !), and;

2. Synchronized application with staggered removal, in which drug is
applied to skin sites at the same time and removed at different times
{Appendix Il).

Study Day Activities

1. Subjects should begin the study sessions at approximately the same
time each study day (within one hour).

2. Verification by history of adequate washout of excluded drugs.

3. The forearm should be free of any dirt or particulate matter that would
interfere with proper drug application or assessment of
pharmacodynamic response. Cleansing of the skin is not encouraged
because of the possible effects on drug uptake and pharmacodynamic
response to the drug product. If necessary, cleansing should be

10


AUEC

1 2 3 4 5 6

Dose Duration (hours)

Figure Alll.1| Observed AUEC,,,,, mean (filled circles) and SEM (upper and lower

limits), and E,,,, model fitted (solid line) to the pooled dose duration-response data of
all 12 subjects in the pilot study.

Note 1:

Note 2:

Note 3:

Data are baseline-adjusted and untreated control-site corrected, thus
AUEC was set to zero at dose duration equal to zero.

The E,,, model fit (solid line) was determined using a population
pharmacokinetic-dynamic data modeling program (P-Pharm, Simed). The
fitted population values were:

EDs: 1.89 hours
Ennax? -48.80 a-scale units times hours

Based on these data, the dose durations selected as the approximate
—D,, for the comparison of test and reference products, and as D, and
D, in the ‘pivotal’ in vivo bioequivalence study were:

Approximate ED,9: 2.0 hours

D,: 1.0 hour
D,: 4.0 hours

29


Table Alll.4 AUEC,.,,, data of all 12 subjects at each dose duration

DD Subject Number
1 2 3 4 5 6
0.25 -1.23 -0.02 -13.87 -27.27 -10.65 -10.41
0.5 -7.39 -5.13 -15.03 -3.71 7.72 -5.94
0.75 -1.48 -8.92 -18.39 -43.82 -23.42 -2.29
1 -3.80 -24.56 -16.25 -44.39 -20.37 -8.92
1.5 -0.23 -19.21 -15.44 -77.04 -19.95 -20.64
2 5.77 -1.80 -23.74 -66.80 -32.00 -19.52
4 -4.74 -43.07 -24.80 -62.96 -32.81 -8.52
6 -1.53 -41.56 -21.79 -71.60 -61.51 -19.01
DD Subject Number
7 8 9 10 11 12
0.25 4.20 -11.95 -12.36 1.15 -30.03 -7.25
0.5 -12.31 7.45 12.95 -39.45 -39.56 14.73
0.75 1.34 5.95 1.88 -40.68 -61.06 -21.09
1-18.84 8.78 -43.35 -16.19 -43.58 10.81
1.5  -42.70 1.26 -20.97 6.87 -40.73 0.51
2 = --37.29 -48.83 -39.79 10.75 -62.01 -10.51
4 -45.46 -71.77 -57.55 -37.64 -27.82 -14.89
6  -37.24 -8.14 -34.18 -35.01 -33.60 16.14

DD:
UNT:
TRT:

Abbreviations in Tables Alll.1 - AlIL4

Dose duration in hours
Untreated control site (no product applied)
Treated site (topical corticosteroid product applied)
Baseline measurement of skin color, as described in Section IV(1)(9)

28


proportion of subjects expected to meet the minimum D,/D, ratio of AUEC values in
the pivotal study. Because outcome of a pilot study may be a function of study

conditions,

including among other factors subject population characteristics,

methodology used to assess skin blanching, and amount of drug product applied, this
Guidance strongly encourages the performance of a pilot study by each study site for
each reference listed drug (RLD) under investigation. Refer to Section !V(J)(3)
regarding consultation with the Division of Bioequivalence concerning-conduct and/or
outcome of a pilot study.

A. Study Design and Analysis

1.

Dose duration-response study based on RLD only, with randomization
of dose duration skin sites.

Dose durations from 0.25 to 6.0 hours, plus untreated control sites on
each arm to enable correction of active drug skin sites for color changes
during the study unrelated to drug exposure. Because the vehicle
corresponding to the RLD is not generally available, untreated control
sites refer to untreated areas of skin, not to areas of skin to which
vehicle has been applied.

Chromameter measurement of the pharmacodynamic response to the
topical corticosteroid at various time periods, rather than a single time
point measurement, following each dose duration application and
removal.

Dose duration-response data should be modeled using either a nonlinear
mixed effect modeling method or a naive pooled data method to
determine the population ED. value which will serve as the approximate
dose duration for the bioequivalence comparison in the pivotal study.

Twelve subjects.

For products marketed in multiple strengths, the pilot and pivotal studies
should be conducted on the high strength product.”

** Waiver of in vivo bioequivalence for lower strengths of a topical dermatologic corticosteroid product will be
considered based on acceptable in vivo bioequivalence data for the high strength product and comparative

formulation data which meet the qualitative sameness (Q,) and quat
Office of Generic Drugs’ Inactive Ingredients Policy for the spe

tive sameness (Q,) requirements of the
ic lower strength product relative to the

comparable strength innovator product. If the inactive ingredients of the lower strength product do not meet the
Q, and Q, requirements relative to the comparable strength innovator product, waiver will be considered with an

explanation.


Prepared by:

Concur:

Concur:

Concur:

Loeatinc, P. A Kana

Date: 2 Taw (29S

Wallace P. Adams, Ph.D.
Reviewer
Division of Bioequivalence

aa ,

Gur Jai PatSidgh, Ph.D. U
Reviewer
Division of Bioequivalence

r

ous ned, 2S

Date: Y Ya ST

eith K. Chan, Ph.D.
Director
Division of Bioequivalence

Date: 6/: z [ 495

La ce J. Lesko, Ph.D.
Associate Director for Research
Office of Generic Drugs

Ny,

¢ te} pti

y ;
Date: Vie bef;

ions
{

Roger L. Williams, M.D.
Associate Director for Science and
Medical Affairs

Center for Drug Evaluation and Research

21


These are the sample means, sample variances, and sample covariance for the individual
evaluable subject average AUEC data. For the example, these are

X_ = -2343 X_ = -2156 Sy, = 323.13 Spe = 80.10 aR = 78.83

Define t as the 95th percentile of the t-distribution for n-1 degrees of freedom. For example,
for n=7, t (6 degrees of freedom) is 1.9432. Now define

G < 1 is required to have a proper confidence interval. If G > 1, the study does not meet the
in vivo bioequivalence requirements. In the example, G = .0930.

Under the assumption that G < 1, calculate

— \2 -
x é Banl. 6 Xx.
K = |S] + Ta -@ + Bloom - 228
XR ORR Srr| ORR Xp

In the example, K = 2.791.

The confidence interval limits may now be calculated:

x é é
— -G—R ¥ t
X. Opn Xp n

1-G

In the example, 90% confidence interval limits are 53.6% and 165.9%, based on the data of
seven evaluable subjects.

36


APPENDIX Il

SYNCHRONIZED APPLICATION WITH STAGGERED REMOVAL:
SCHEMATIC FOR A SUGGESTED PILOT STUDY PROTOCOL

Figure All.1

Baseline (BL) Measurement, Drug Application and Drug Removal

4
ay
oy sopmnon woah
cm von
|e!

cue §
c] aes

wt
1 2 3 4 5 6

tT Hours After Drug Application

Figure All.2

Skin Blanching Measurements

¢ Application Time

J Measurement Time

4 44

Poor te Spm

1 Y
0 2 4 6 8 10 12 14 16 18 20 22 24 26 2
} Hours After Drug Application

25



based on topical application of a corticosteroid-containing formulation for a period of
6 to 16 hours in healthy human subjects, followed by visual estimation by a trained,
blinded observer of the degree of blanching on a multiple unit scale (O - 3 or O - 4), at
a single time point, usually two hours, after removal of the formulation. Most of the
currently available generic topical corticosteroids have been approved on the basis of
the vasoconstrictor assay as described in this paragraph, or a variant thereof, by OGD
after consultation with the Division of Topical Drug Products. These studies were
conducted prior to 1 July 1992.

The Guidance suggests conducting two in vivo studies - a pilot dose duration-response
study and a pivotal in vivo bioequivalence study comparing test and reference
products. The pilot study characterizes the dose duration-response relationship for the
drug in terms of the E,,,, model (Section Ill) and is conducted solely with the reference
listed drug (RLD). The dose duration method as recommended in this guidance for
documentation of bioequivalence is based on three dose durations: EDso, D, and D,.
The comparison of test and reference products in the pivotal study is conducted at a
dose duration approximately equal to the population ED,. determined in the pilot study.
Sensitivity in the pivotal study is established through dosing of the RLD calibrators at
two dose durations, D, (the shorter dose duration calibrator) and D, (the longer dose
duration calibrator). The guidance recommends that D, equal approximately 0.5 times
EDgo, and D, equal approximately 2 times EDs9 determined from the pilot study.
Because each subject becomes a ‘detector’ in the study, only the data of those
subjects whose D,/D, ratio of pharmacodynamic responses meets a specified minimum
value may be included in the data and statistical analyses supporting in vivo
bioequivalence. The proposed methodology is more fully explained in subsequent
sections of the guidance.

PHARMACODYNAMIC EFFECT STUDIES: THE VASOCONSTRICTOR ASSAY

Regulatory concerns regarding the vasoconstrictor assay, as it is currently performed,
focus on two interrelated aspects of the methodology: 1) its validation and
standardization as a bioassay; and 2) the use of a trained observer to measure
vasoconstrictor response.

A. Validation and Standardization

Application of the vasoconstrictor assay to a determination of bioequivalence
of a topical corticosteroid rests on the assumption that the vasoconstrictor
properties of a topical corticosteroid can be utilized to establish a standard,
validated bioassay. Development and validation of any assay, including a
bioassay, involves certain documentation. Elements of this documentation that
are of interest to scientists in the Center for Drug Evaluation and Research
(CDER) were discussed at a December 1990 workshop cosponsored by the
Food and Drug Administration, the American Association of Pharmaceutical
Scientists, the Federation Internationale Pharmaceutique, the Canadian Health
Protection Branch, and the Association of Official Analytical Chemists. A
summary of the conclusions of this workshop has been published.*

3


d. Determine the EDs, (the dose duration corresponding to half-
maximal response).

e. Determine D, and D, corresponding to approximately one-half
EDs, and two times ED,o, respectively, for use in the pivotal
study.""” These values bracket EDs, correspond to
approximately 33% and 67% respectively of the maximal
response, and represent the sensitive portion of the dose
duration-response curve.®

2. Visual Data [refer to Section III(B)]

a. Compute the area under the effect curve (AUEC) for each
vasoconstriction time profile.

b. Fit the dose duration-response data as described in Section
IV(J)(1){c).
c. Determine the EDs», D,, and D,.
3. Consultation with the Division of Bioequivalence

If a sponsor wishes to discuss issues related to assay validation, dose
duration-response, or other aspects of its pilot dose duration-response
study prior to the conduct of the pivotal in vivo bioequivalence study,
the sponsor has the option to submit the study data and summary
results of the pilot study to the Division of Bioequivalence for review of
EDso, D,, and D, values, and the proposed pivotal study protocol. If the
pilot study results are submitted, the firm may wish to include all study
data, with an explanation accompanying any data not included in the
pharmacodynamic analysis.

Sponsors may consider that they have sufficient information about the
dose duration-response relationship of the topical corticosteroid under
investigation to proceed directly to the pivotal study without conduct of
the pilot study. This course of action assumes knowledge of EDgo, Dy,
and D, appropriate to the RLD under study site conditions, which is
essential to an acceptable pivotal study. Staff in the Division of
Bioequivalence are available to review this information at the request of
a sponsor.

“" The observed EDs value may be rounded by up to 15 minutes to obtain the EDso value used in the pivotal
study. In practice, a demonstration of dose duration-response based on D, within 0.25 - 0.5 times the observed
EDs and D, within 2 - 4 times the observed ED,o is acceptable. For potent corticosteroids with short EDs values,
these recommendations may require adjustment. If so, the Division of Bioequivalence may be consulted.

14


Subject Screening for Response

Consult Section IV(E).

Assay Precision

Consult Section IV(F).

Study Day Activities

1.

2.

Consult Section IV(I}, where applicable.

Application of dose durations to skin sites on the ventral forearms of
each subject should be randomly assigned, maintaining the
recommendations described below. Sites may be occluded or
nonoccluded, based on the considerations of Section IV(G) and the pilot
study results. Untreated control skin sites should also be included for
studies based on chromameter measurements. Dose durations and
control sites on each arm should include:

T: the test product at the dose duration corresponding
approximately to EDs, as determined with the reference listed
drug (RLD) in the pilot study (two sites per arm);

R: the reference listed drug (RLD) at the same dose duration
corresponding approximately to EDs, as for the test product T
(two sites per arm);

D;: the shorter dose duration RLD calibrator (one site per arm);
D,: the longer dose duration RLD calibrator (one site per arm); and
UNT: the untreated control (two sites per arm).

The total number of testing sites is 16 (eight sites per arm). The eight
treatments should be randomized, as noted above. Application patterns
on each arm should be complementary, i.e., D, is complementary to D,,
R is complementary to T, and UNT is complementary to UNT. As
examples, where T is assigned a specific skin site location on one arm,
R should be assigned to the corresponding skin site on the other arm.
Where UNT is assigned a specific skin site location on one arm, UNT
should be assigned to the corresponding skin site on the other arm.

16


data to support waiver of in vivo bioequivalence of the lower strength(s) of topical
corticosteroid products, scale-up of production batches, and approval of formulation,
process, and site changes in the absence of in vivo data. Future use of these data as
a quality control tool is also envisioned.

The Guidance has been prepared by staff of the Division of Bioequivalence (HFD-650),
with the participation of staff of the Division of Topical Drug Products (HFD-540) and
the Division of Biometrics (HFD-710). It is a general guidance intended to apply to
topical corticosteroids of all potency groups. Because dose duration-response
characteristics may vary with the particular drug of interest, as well as with study
conditions, the Guidance encourages the performance of a pilot study to define
appropriate parameters for the pivotal study. Staff members of HFD-650 are available
to work with pharmaceutical sponsors in the design of specific studies to meet the
recommendations of the Guidance.

BACKGROUND

The determination of bioequivalence of two solid oral dosage forms generally rests on
a comparison of drug and/or metabolite concentrations in an accessible biologic fluid,
such as blood or urine, after administration of a single or multiple doses of each drug
product to healthy volunteers. In the absence of this methodology, the Food and Drug
Administration may, through provisions of the Food, Drug and Cosmetic Act and
implementing regulations (21 CFR § 320), rely on other in vivo and in vitro methods
to assess bioequivalence. In descending order of preference within the Office of
Generic Drugs, these methods include: 1) pharmacodynamic effect studies; 2) clinical
trials, 3) in vivo animal studies; and 4) in vitro studies. Although the methods in the
latter two categories are acceptable from a statutory/regulatory standpoint, the
Division of Bioequivalence in OGD historically has relied only on in vivo
pharmacodynamic or clinical studies to assess bioequivalence of drug products that do
not produce measurable concentrations of drug or metabolite in an accessible biological
fluid. Clinical trials generally require large numbers of subjects and often lack
sensitivity. In contrast, pharmacodynamic effect studies offer the possibility of
developing acceptable bioequivalence data in a relatively small number of subjects.

For many years, the Division of Bioequivalence has relied on pharmacodynamic effect
methodology to approve generic topical corticosteroid drug products. The approach
is based on the property of corticosteroids to produce blanching or vasoconstriction
in the microvasculature of the skin. This property presumably relates to the amount
of drug entering the skin? and thus becomes a possible basis for the comparison of
drug delivery from two potentially equivalent topical corticosteroid formulations.
Development of the methodology is attributed to Dr. R.B. Stoughton and Dr. A.W.
McKenzie, who initially developed it as a means to assess potency of different topical
corticosteroids.? Subsequently it was applied by pharmaceutical manufacturers and
accepted by the Food and Drug Administration as a means of assessing bioavailability
and bioequivalence. In these and other applications, it is referred to variously as the
Stoughton-McKenzie test, the vasoconstrictor assay, or the skin blanching assay.
Although there are many forms of the vasoconstrictor assay, the general method is


APPENDIX V
LOCKE’S METHOD: FORMULAE AND A WORKED EXAMPLE
The calculation of the 90% confidence interval for the ‘pivotal’ bioequivalence data set of Table

AIV.6 is given below, The data used to calculate the confidence interval are the average AUEC
values of ‘detectors’ (evaluable subjects) only.

Table AV.1 Average AUEC values of subjects in the ‘pivotal’ study meeting the dose duration-
response criterion of Section V(H)(1)(c)

Subject AVEC .24) AUECo.24
Test Product Reference Product
(Average) (Average)

2 -48.52 -22.20

3 -38.99 -18.65

4 -7.62 -22.42

7 0.98 -10.96

9 -32.05 -37.40

1 -26.18 -26.73

12 -11,62 -12.56

The calculation of the confidence interval is facilitated by the calculation of the following
intermediate quantities:

n
2 Xr
i=l

pie

= 1 =
Xp =e » Xy, Xp =

n
where n is the number of evaluable subjects, seven (7) in this example.

» Cy, - X,)
i=l

cr =

» (By - X,)
a — ist

6.

35


13.

14,

Schuirmann DJ. Confidence intervals for the ratio of two means from a crossover
study. In: Proceedings of the biopharmaceutical section, American Statistical
Association, Washington, DC 1989; 121-6.

Locke CS. An exact confidence interval from untransformed data for the ratio of two
formulation means. J Pharmacokinet Biopharm 1984;12:649-55.

23


GUIDANCE”
TOPICAL DERMATOLOGIC CORTICOSTEROIDS:
IN VIVO BIOEQUIVALENCE

Issue Date: 2 June 1995

1, INTRODUCTION

This Guidance provides recommendations to pharmaceutical sponsors on methods to
document in vivo bioequivalence of topical dermatologic corticosteroids, hereinafter
referred to as topical corticosteroids. The Guidance becomes effective 2 June 1995.
Any investigations initiated after that date should generally conform to the
recommendations of the Guidance. The Guidance utilizes a pharmacodynamic
approach, based on an update of the Stoughton-McKenzie vasoconstrictor bioassay,
to assess bioequivalence of topical corticosteroids. The method utilizes a duration of
exposure (dose duration) approach to control the dose of topical corticosteroid that is
delivered. The proposed methodology includes a pilot dose duration-response study
to determine the appropriate dose duration for use in the pivotal study, followed by the
pivotal in vivo bioequivalence study incorporating replicate design and documentation
of acceptable individual subject dose duration-response. As with all bioanalytical
methods, this pharmacodynamic bioassay will require careful validation on the part of
pharmaceutical sponsors.

Potent topical corticosteroid products may suppress the hypothalamic-pituitary-adrenal
(HPA) axis. In the past, when in vivo bioequivalence of such products was
documented using the single time point Stoughton-McKenzie study design, the Office
of Generic Drugs (OGD) required an HPA axis suppression test when test and reference
formulations were significantly different. Products documented to be bioequivalent
using this Guidance will not be required to submit HPA axis suppression test data.

The 1 July 1992 Interim Guidance, Topical Corticosteroids: In Vivo Bioequivalence and
In Vitro Release Methods' included dermatopharmacokinetic (skin stripping) studies
and jn vitro release studies. The agency currently has insufficient data to recommend
skin stripping methods to document bioequivalence of topical corticosteroids.
However, this methodology for documentation of bioequivalence may be used if
appropriate validation data are provided. At the present time, OGD will not require in
vitro release data to support approval of ANDA’s for topical corticosteroids. Following
future recommendations of the Scale-Up and Post-Approval Changes for Semisolids
{SUPAC-SS) Working Group, OGD may recommend the submission of in vitro release

* This statement has been prepared by the Division of Bioequivalence in the Office of Generic Drugs, with the
participation of the Division of Topical Drug Products in the Office of Drug Evaluation II and the Di ision of
Biometrics in the Office of Epidemiology and Biostatistics. it is an informal communication under
21 CFR 10.90(b)(9) that represents the best judgment of the two reviewing divisions at this time. This statement
does not necessarily represent the formal position of the Center for Drug Evaluation and Research, Food and Drug
Administration, and does not bind or otherwise obligate the Center for Drug Evaluation and Research. For
information about this guidance, contact the Division of Bioequivalence, 7500 Standish Place, Metro Park North,
Rockville, MD 20855 (Phone: 301-594-2290; Fax: 301-594-0181).



Table AIV.2 Baseline-adjusted a-scale data for a subject

SUB TRT ARM LOC. SITE BL Hours after drug removal
oO 2 4 6 19 24

1 A R 1 UNT - -0.11 0.75 0.30 0.48 0.34 1.37
1 A R 1 TRT - 0.75 0.48 -1.19 -0.88 -0.79 0.19
1 B R 2 = =UNT - 1.20 1.08 0.67 1.17 0.96 1.69
1 B R 2 = TRT +  -0.50 -0.67 -2.34 -0.91 -0.78 0.47
1 Cc R 3° ~UNT - 1.04 1.52 0.49 1.47 0.31 1.27
1 c R 3 TRT - 1.48 1.52 -0.36 0.46 -0.38 0.81
1 D R 4  UNT - 0.88 1.30 0.25 1.57 0.21 0.82
1 D R 4  TRT - 0.84 -0.44 -2.31 -0.40 -0.14 0.53
1 c L 1 UNT : 0.36 -0.06 -0.14 -0.38 -0.89 -0.13
1 Cc L 1 TRT - -1,55 -1.58 -2.58 -2.18 -1.21 -0.52 n
1 B L 2 UNT -  -0.80 -0.36 -0.87 -0.38 -0.32 0.46
1 B L 2 TRT - -2.98 -3.08 -3.35 -3.07 -1.19 -0.21
1 A L 3 UNT - +0.66 0.04 -0.48 0.18 0.20 0.69
1 A L 3 ~TRT - +0.24 -0.92 -2.25 -2.46 -1.85 -0.74
1 D L 4 UNT -  +0.71 -0.04 -0.49 0.11 0.06 0.94
1 D L 4  TRT - +0.76 -2.09 -3.29 -3.66 -1.75 -0.84

Table AIV.3 Baseline-adjusted, untreated control site-corrected a-scale data and AUECo24
data for a subject

SUB TRT ARM LOC. SITE BL Hours after drug removal AUEC 9.24)
fo) 2 4 6 19 24
1 A R 1 TRT - 0.86 -0.27 -1.49 -1.36 -1.13 -1.18 -25.98
1 B R 2 TRT + -1.70 -1.75 -3.01 -2.08 -1.74 -1.22 -45.53
1 c R 3 TRT - 0.44 0.00 -0.85 -1.01 -0.69 -0.46 -16.20
1 Do R 4 TRT -  -0.04 -1.74 -2.56 -1.97 -0.35 -0.29 -27.29
1 c L 1 TRT -  -1.91 -1,52 -2.44 -1.80 -0.32 -0.39  -27.19
1 B L 2 TRT -  -2.18 -2.72 -2.48 -2.69 -0.87 -0.67 -42.26
1 A L 3 TRT - 0.42 -0.96 -1.77 -2.64 -2.05 -1.43  -46.87
1 D L 4 TRT -  -0.05 -2.05 -2.80 -3.77 -1.81 -1.78 -58.77

31


APPENDIX Ill

ANALYSIS OF DATA FROM AN AGENCY-SPONSORED PILOT STUDY:
AN EXAMPLE

Development of the recommended study designs in this guidance included the conduct in late
1994 and early 1995 under agency contract [Section III(C)] of small-scale vasoconstrictor
assays at two research sites: the University of Utah Health Sciences Center and the University
of California, San Diego, School of Medicine. The University of Utah study used the
synchronized application with staggered removal method, while the University of California
study used the staggered application with synchronized removal method. Each research site
conducted a pilot dose duration-response study and a ‘pivotal’ in vivo bioequivalence study,
with 12 subjects in each of the four studies. The contract studies differed in several ways
from those recommended in this guidance. The contract studies (1) used untreated control
sites corresponding to each active drug site, (2) measured skin blanching through 48 hours,
and (3) did not replicate the test and reference products on each arm (‘pivotal’ study).

No preference in methodology is intended by use of data based on the staggered application
with synchronized removal method in Appendices III - V to illustrate data analysis. Either
method of application and removal is acceptable. Table Alll.1 presents chromameter a-scale
taw data of the University of California pilot study for subject 1 through 24 hours. Baseline-
adjusted data are presented in Table Alll.2, and baseline-adjusted, untreated control site-
corrected data are presented in Table Aill.3. In this example data set, each active drug site
was corrected for its corresponding untreated control site. However, the guidance
recommends use of only two untreated control sites per arm, and subtracting their average
from all active drug sites on that arm. Table Alll.4 presents AUEC,, 4, data for all subjects and
dose durations. The E,,,, model fit to the pooled data is shown in Figure Alll.1.

Table Alll.1 Chroma Meter (Minolta) a-scale readings for a subject

SUB DD SITE BL Hours after drug removal
1°) 2 4 6 19 24

0.25 UNT 9.86 9.99 10.10 9.52 10.03 10.40 9.65
0.25 TRT 10.36 9.89 10.38 10.32 10.51 10.86 10.04
0.5 UNT 9.27 8.20 9.78 8.54 9.61 9.87 9.59
0.5 TRT 9.59 8.77 9.35 9.27 8.78 10.40 9.82
0.75 UNT 8.45 8.75 8.24 8.16 8.92 8.43 8.22
0.75 TRT 8.46 8.66 8.53 8.04 8.26 8.72 8.56

1 UNT 9.00 9.63 8.45 8.03 8.94 9.33 9.66

1 TRT 8.52 8.80 8.87 8.53 8.05 8.66 8.21
1.5 UNT 9.44 9.39 9.46 9.27 9.92 9.59 9.01
1.5 TRT 9.59 9.60 9.99 9.93 9.18 10.23 9.24
UNT 10.12 10.13 9.50 9.93 9.39 10.95 10.84
TRT 10.28 10.25 10.68 10.15 10.31 11.46 8.92
UNT 8.89 8.01 8.78 8.89 9.76 8.48 9.18
TRT 8.21 8.28 8.36 7.98 7.96 8.15 8.30
UNT 9.18 9.46 8.79 8.03 9.29 10.11 9.51
TRT 9.37 9.61 9.30 8.92 9.20 10.16 9.63

DAORPANN

Appendix ill abbreviations appear on page 28.

26


Prior to measurement of the pharmacodynamic response at the end of
the application period, remaining topical corticosteroid should be gently
removed from the skin. This may be accomplished by either of the
methods below.

Three consecutive swabbings with dry cotton swabs.

Suitable for either the staggered application with synchronized
removal method, or the synchronized application with staggered
removal method.

Washing all skin sites with mild skin cleanser and water, blotting
the sites dry with a nonabrasive towel, and allowing to air-dry for
at least five minutes prior to evaluation. If after five minutes the
subject has any visible cutaneous effects related to washing, a
longer waiting period may be necessary.

i. Suitable for the staggered application with synchronized
removal method.

ii. Cleanse arm surfaces with a minimum amount of skin
cleanser, for example one drop of a liquid cleanser worked
to a lather in wetted hands, followed by rinsing.

iii. Examples of mild liquid skin cleansers are Purpose’ Gentle
Cleansing Wash (Johnson & Johnson), and Cleansing
Wash (Neutrogena).

Assessment of baseline skin color and skin blanching at each site.
Examples of assessment time periods are:

a.

For staggered application with synchronized removal:

For all dose durations and untreated contro! sites, baseline
readings within one hour prior to drug application of the longest
dose duration, and at O, 2, 4, 6, 19, and 24 hours after drug
product removal (Appendix 1).

Time zero equals time of drug product removal.

For synchronized application with staggered removal:

For all dose durations and untreated control sites, baseline
readings within one hour prior to the time of drug application to
active drug sites, and 6, 8, 11, 24, and 28 hours after drug
product application (Appendix fl).

Time zero equals time of drug product application.

12


Computer Formatted Data Submission

If the study data and summary results are submitted, a diskette in the
ASCII format containing the study data should be submitted with the
pilot study. Chromameter raw data; baseline-adjusted data; baseline-
adjusted, untreated control site-corrected data; and AUEC data should
be arranged in separate files in the format given in Tables Alll.1 - Alll.4,

PIVOTAL /N V/VO BIOEQUIVALENCE STUDY

The purpose of the pivotal study is to document in vivo bioequivalence of the test
product to the reference listed drug (RLD). The guidance specifies the minimum dose
duration-response ratio which must be met by individual subjects for inclusion in the
data analysis. Therefore, a pivotal study may generally be initiated without
consultation with the Division of Bioequivalence [Section IV(J)(3)].

A.

Study Design

1.

Pharmacodynamic bioequivalence study using within-study day replicate
single dose durations of test and reference products, and based on the
population ED, identified in the pilot study.

Individual subject dose duration-response, based upon an acceptable
D,/D, ratio of AUEC values of the RLD. The minimum value of the ratio
should be 1.25. Success in meeting this dose duration-response
criterion will be determined through duplicate dosing of the RLD at D,,
the dose duration equal to approximately 0.5 times the population EDso,
and at D,, the dose duration equal to approximately 2 times the
population EDgo.

Forty to sixty evaluable subjects, i.e., subjects who meet the
‘responder’ and ‘detector’ criteria of Sections IV(E) and V(H)(1){c).

Subject Inclusion Criteria

Consult Section IV(B).

Subject Exclusion Criteria

Consult Section IV(C).

Study Restrictions

Consult Section IV(D).

15