Guidance for Industry
Extended Release Oral Dosage Forms:
Development, Evaluation, and
Application of In Vitro/In Vivo
Correlations
U.S. Department of Health and Human Services
Food and Drug Administration
Center for Drug Evaluation and Research (CDER)
September 1997
BP 2 Guidance for Industry
Extended Release Oral Dosage Forms:
Development, Evaluation, and
Application of In Vitro/In Vivo
Correlations
Additional copies are available from:
Office of Training and Communications 
Division of Communications Management
The 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 of Health and Human Services
Food and Drug Administration
Center for Drug Evaluation and Research (CDER)
September 1997
BP 2 Table of Contents
I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
II. BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
III. CATEGORIES OF IN VITRO/IN VIVO CORRELATIONS . . . . . . . . . . . . . . . . . . 3
A. Level A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
B. Level B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
C. Level C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
D. Multiple Level C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
IV. GENERAL CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
V. DEVELOPMENT AND EVALUATION OF A LEVEL A IN VITRO/IN VIVO
CORRELATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
A. Developing the Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
B. Evaluating the Predictability of a Level A Correlation . . . . . . . . . . . . 6
VI. DEVELOPMENT AND EVALUATION OF A LEVEL C IN VITRO/IN VIVO
CORRELATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
VII. APPLICATIONS OF AN IVIVC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
A. Biowaivers for Changes in the Manufacturing of a Drug Product . . 11
B. Setting Dissolution Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
DEFINITION OF TERMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
i GUIDANCE FOR INDUSTRY1
Extended Release Oral Dosage Forms:
Development, Evaluation, And Application
Of In Vitro/In Vivo Correlations
I. INTRODUCTION
This guidance provides recommendations to pharmaceutical sponsors who intend to develop
documentation in support of an in vitro/in vivo correlation (IVIVC) for an oral extended release
(ER) drug product for submission in a new drug application (NDA), abbreviated new drug
application (ANDA), or antibiotic drug application (AADA).  The guidance presents a
comprehensive perspective on (1) methods of developing an IVIVC and evaluating its
predictability; (2) using an IVIVC to set dissolution specifications; and (3) applying an IVIVC as
a surrogate for in vivo bioequivalence when it is necessary to document bioequivalence during the
initial approval process or because of certain pre- or  postapproval changes (e.g., formulation,
equipment, process, and manufacturing site changes).
II. BACKGROUND
The concept of  IVIVC, particularly for ER drug products, has been extensively discussed by
pharmaceutical scientists.  The ability to predict, accurately and precisely, expected bioavailability
characteristics for an ER product from dissolution profile characteristics is a long sought after
goal.  Several workshops and publications have provided information in support of this goal. 
These are discussed briefly as follows:
! A report from a 1987 ASCPT/DIA/APS/FDA-sponsored workshop entitled Report of the
Workshop on CR Dosage Forms: Issues and Controversies (1987) indicated that the state
of science and technology at that time did not permit consistently meaningful IVIVC for
ER dosage forms and encouraged IVIVC as a future objective. Dissolution testing was
considered useful only for process control, stability, minor formulation changes, and
manufacturing site changes.
1 This guidance has been prepared by the Extended Release Dissolution Working Group of the
Biopharmaceutics Coordinating Committee (BCC) in the Center for Drug Evaluation and Research (CDER) at the Food
and Drug Administration (FDA).  This guidance represents the Agencys current thinking on in vitro/in vivo correlations
for extended release oral dosage forms.  It does not create or confer any rights for or on any person and does not operate
to bind FDA or the public.  An alternative approach may be used if such approach satisfies the applicable statute,
regulations, or both.   ! A USP PF Stimuli Article in July 1988 established the classification of IVIVC into Levels
A, B and C, which are currently in use.
! A report from a 1990 ASCPT/DIA/APS/FDA-sponsored workshop entitled In vitro/In
vivo Testing and Correlation for Oral Controlled/Modified Release Dosage Forms
(1990) concluded that, while the science and technology may not always permit
meaningful IVIVC, the development of an IVIVC was an important objective on a
product-by-product basis.  Procedures for development, evaluation, and application of an
IVIVC were described.  Validation of dissolution specifications by a bioequivalence study
involving two batches of product with dissolution profiles at the upper and lower
dissolution specifications was suggested.
! USP Chapter 1088 similarly describes techniques appropriate for Level A, B, and C
correlations and methods for establishing dissolution specifications.
! Further information related to IVIVCs was developed in a USP/AAPS/FDA-sponsored
workshop, which resulted in a report entitled Workshop II Report: Scale-up of Oral
Extended Release Dosage Forms (1993).  This report identified the objectives of an
IVIVC to be the use of dissolution as a surrogate for bioequivalency testing, as well as an
aid in setting dissolution specifications.  The report concluded that dissolution may be
used as a sensitive, reliable, and reproducible surrogate for bioequivalence testing. The
report gave support to the concepts of USP Chapter 1088 and further found that an
IVIVC may be useful for changes other than minor changes in formulation, equipment,
process, manufacturing site, and batch size.
These reports document increasing confidence in IVIVC to estimate the in vivo bioavailability
characteristics for an ER drug product. In this regard, increased IVIVC activity in NDA
submissions has been apparent.  Still, the complete process of developing an IVIVC with high
quality and predictability and identifying specific applications for such correlations has not been
well defined.      
As part of the process of developing this guidance, the Agency conducted several surveys of
NDA submissions for ER drug products to find out the number of times that IVIVCs were
developed. The first survey included NDA submissions from 1982-1992 and found 9 IVIVCs in
60 submissions.  A more recent survey included NDA submissions from October 1994 to October
1995 and found 9 IVIVCs in 12 submissions. 
This guidance is based on these prior deliberations and publications as well as on current
understanding at the FDA and elsewhere on approaches to developing reliable and useful IVIVCs. 
This guidance describes the levels of correlations that can be established with varying degrees of
usefulness, important considerations for in vivo and in vitro experimentation, evaluation of the
correlation by focusing on the critical feature of predictability, and practical applications that can
be achieved using the IVIVC.  With the availability of this guidance, sponsors are encouraged to
2 develop IVIVCs for ER products in the expectation that the information will be useful in
establishing dissolution specifications and will permit certain formulation and manufacturing
changes without an in vivo bioequivalence study.
III. CATEGORIES OF IN VITRO/IN VIVO CORRELATIONS
A. Level A
A Level A correlation2 is usually estimated by a two-stage procedure: deconvolution
followed by comparison of the fraction of drug absorbed to the fraction of drug dissolved. 
A correlation of this type is generally linear and represents a point-to-point relationship
between in vitro dissolution and the in vivo input rate (e.g., the in vivo dissolution of the
drug from the dosage form).  In a linear correlation, the in vitro dissolution and in vivo
input curves may be directly superimposable or may be made to be superimposable by the
use of a scaling factor. Nonlinear correlations, while uncommon, may also be appropriate.  
Alternative approaches to developing a Level A IVIVC are possible. One alternative is
based on a convolution procedure that models the relationship between in vitro dissolution
and plasma concentration in a single step.  Plasma concentrations predicted from the
model and those observed are compared directly.  For these methods, a reference
treatment is desirable, but the lack of one does not preclude the ability to  develop an
IVIVC.
Whatever the method used to establish a Level A IVIVC, the model should predict the
entire in vivo time course from the in vitro data.  In this context, the model refers to the
relationship between in vitro dissolution of an ER dosage form and an in vivo response
such as plasma drug concentration or amount of drug absorbed.
B. Level B
A Level B IVIVC uses the principles of statistical moment analysis.  The mean in vitro
dissolution time is compared either to the mean residence time or to the mean in vivo
dissolution time. A Level B correlation, like a Level A, uses all of the in vitro and in vivo
data, but is not considered to be a point-to-point correlation. A Level B correlation  does
not uniquely reflect the actual in vivo plasma level curve, because a number of different in
vivo curves will produce similar mean residence time values.
2 Level A correlations are the most common type of correlation developed in NDAs submitted to the FDA. 
Level B correlations are rarely seen in NDAs; multiple Level C correlations are seen infrequently.
3 C. Level C
A Level C IVIVC establishes a single point relationship between a dissolution parameter,
for example, t , percent dissolved in 4 hours and a pharmacokinetic parameter (e.g.,
50%
AUC, C ,  T ).  A Level C correlation does not reflect the complete shape of the plasma
max max
concentration time curve, which is the critical factor that defines the performance of ER
products. 
D. Multiple Level C
A multiple Level C correlation relates one or several pharmacokinetic parameters of
interest to the amount of drug dissolved at several time points of the dissolution profile. 
IV. GENERAL CONSIDERATIONS:
The following general statements apply in the development of an IVIVC in an NDA or
ANDA/AADA:
! Human data should be supplied for regulatory consideration of an IVIVC. 
! Bioavailability studies for IVIVC development should be performed with enough subjects
to characterize adequately the performance of the drug product under study.  In prior
acceptable data sets, the number of subjects has ranged from 6 to 36.  Although crossover
studies are preferred, parallel studies or cross-study analyses may be acceptable.  The
latter may involve normalization with a common reference treatment. The reference
product in developing an IVIVC may be an intravenous solution, an aqueous oral solution,
or an immediate release product.
! IVIVCs are usually developed in the fasted state. When a drug is not tolerated in the
fasted state, studies may be conducted in the fed state.
! Any in vitro dissolution method may be used to obtain the dissolution characteristics of
the ER dosage form.  The same system should be used for all formulations tested. 
! The preferred dissolution apparatus is USP apparatus I (basket) or II (paddle), used at
compendially recognized rotation speeds (e.g., 100 rpm for the basket and  50-75 rpm for
the paddle). In other cases, the dissolution properties of some ER formulations may be
determined with USP apparatus III (reciprocating cylinder) or IV (flow through cell).  
Appropriate review staff in CDER should be consulted before using any other type of
apparatus.
4 ! An aqueous medium, either water or a buffered solution preferably not exceeding pH 6.8,
is recommended as the initial medium for development of an IVIVC.  Sufficient data
should be submitted to justify pH greater than 6.8.  For poorly soluble drugs, addition of
surfactant (e.g., 1% sodium lauryl sulfate) may be appropriate. In general, nonaqueous and
hydroalcoholic systems are discouraged unless all attempts with aqueous media are
unsuccessful. Appropriate review staff in CDER should be consulted before using any
other media.
! The dissolution profiles of at least 12  individual dosage units from each lot should be
determined.  A suitable distribution of sampling points should be selected to define
adequately the profiles. The coefficient of variation (CV) for mean dissolution profiles of a
single batch should be less than 10%.
! A Level A IVIVC is considered to be the most informative and is recommended, if
possible.
! Multiple Level C correlations can be as useful as Level A correlations.  However, if a
multiple Level C correlation is possible, then a Level A correlation is also likely and is
preferred.
! Level C correlations can be useful in the early stages of formulation development when
pilot formulations are being selected.  
! Level B correlations are least useful for regulatory purposes.
! Rank order correlations are qualitative and are not considered useful for regulatory
purposes.
V. DEVELOPMENT AND EVALUATION OF A LEVEL A IN VITRO/IN VIVO
CORRELATION
A. Developing the Correlation
The most commonly seen process for developing a Level A IVIVC is to (1) develop
formulations with different release rates, such as slow, medium, fast, or a single release
rate if dissolution is condition independent; (2) obtain in vitro dissolution profiles and in
vivo plasma concentration profiles for these formulations; (3) estimate the in vivo
absorption or dissolution time course using an appropriate deconvolution technique for
each formulation and subject (e.g., Wagner-Nelson, numerical deconvolution). These three
steps establish the IVIVC model. Alternative approaches to developing Level A IVIVCs
are possible. Further general information follows:
5 ! The IVIVC relationship should be demonstrated consistently with two or more
formulations with different release rates to result in corresponding differences in
absorption profiles.  Although an IVIVC can be defined with a minimum of two
formulations with different release rates, three or more formulations with different
release rates are recommended.  Exceptions to this approach (i.e., use of only one
formulation) may be considered for formulations for which in vitro dissolution is
independent of the dissolution test conditions (e.g., medium, agitation, pH). 
! Ideally, formulations should be compared in a single study with a crossover design.
! If one or more of the formulations (highest or lowest release rate formulations)
does not show the same relationship between in vitro dissolution and in vivo
performance compared with the other formulations, the correlation may still be
used within the range of release rates encompassed by the remaining formulations.
! The in vitro dissolution methodology should adequately discriminate among
formulations.  Dissolution testing can be carried out during the formulation
screening stage using several methods.  Once a discriminating system is developed,
dissolution conditions should be the same for all formulations tested in the
biostudy for development of the correlation and should be fixed before further
steps towards correlation evaluation are undertaken.
! During the early stages of correlation development, dissolution conditions may be
altered to attempt to develop a 1-to-1 correlation between the in vitro dissolution
profile and the in vivo dissolution profile.
! Time scaling may be used as long as the time scaling factor is the same for all
formulations. Different time scales for each formulation indicate absence of an
IVIVC.
B. Evaluating the Predictability of a Level A Correlation
An IVIVC should be evaluated to demonstrate that predictability of in vivo performance
of a drug product from its in vitro dissolution characteristics is maintained over a range of
in vitro dissolution release rates and manufacturing changes. Since the objective of
developing an IVIVC is to establish a predictive mathematical model describing the
relationship between an in vitro property and a relevant in vivo response, the proposed
evaluation approaches focus on the estimation of predictive performance or, conversely,
prediction error.  Depending on the intended application of an IVIVC and the therapeutic
index of the drug, evaluation of prediction error internally and/or externally may be
appropriate. Evaluation of internal predictability is based on the initial data used to define
the IVIVC model. Evaluation of external predictability is based on additional test data 
6 sets. Application of one or more of these procedures to the IVIVC modeling process
constitutes evaluation of predictability. 
An important concept is that the less data available for initial IVIVC development and
evaluation of predictability, the more additional data may be needed to define completely
the IVIVC's predictability.  Some combination of three or more formulations with
different release rates is considered optimal.
Another significant factor is the range of release rates studied.  The release rates, as
measured by percent dissolved, for each formulation studied, should differ adequately
(e.g., by 10%). This should result in in vivo profiles that show a comparable difference, for
example, a 10% difference in the pharmacokinetic parameters of interest (C  or AUC)
max
between each formulation.
 
Methodology for the evaluation of IVIVC predictability is an active area of investigation
and a variety of methods are possible and potentially acceptable. A correlation should
predict in vivo performance accurately and consistently. Once this relationship has been
achieved, in vitro dissolution can be used confidently as a surrogate for in vivo
bioequivalence of ER drug products in the situations described below.
1. Experimental Data Considerations
a. Dosage Form Properties:  Dependence of In Vitro Release on
Experimental Conditions
Condition independent dissolution:  If in vitro dissolution is shown to be
independent of dissolution conditions (e.g., pH and agitation) and if the in vitro
dissolution profile is shown to be equal to the in vivo absorption or in vivo
dissolution profile, then the results for a single formulation (one release rate) may
be sufficient.  Evaluation of data for this formulation and evaluation of additional
test data sets, as appropriate, for the purpose of estimation of internal and/or
external predictability are recommended.
Condition dependent dissolution:  In all other instances where an IVIVC model is
presented, results from a single formulation (one release rate) should be considered
insufficient. To estimate internal and/or external predictability, evaluation of data
from two or more formulations with different release rates is recommended.
b. Internal and External Predictability
Two distinct aspects of predictability can be considered.  However, both aspects
are not recommended in all instances.
7 Estimation of prediction error internally:  The first aspect relates to evaluating
how well the model describes the data used to define the IVIVC and is appropriate
in all instances.
If formulations with three or more release rates are used to develop the IVIVC
model, no further evaluation beyond this initial estimation of prediction error may
be necessary for non-narrow therapeutic index drugs (Category 2 a and b
applications, see page 12).  However, depending on the results of this internal
prediction error calculation, determination of prediction error externally may be
appropriate.
If only two formulations with different release rates are used, the application of the
IVIVC is further limited to Category 2a applications (see page 12). In this
circumstance, determination of prediction error externally is recommended for
complete evaluation and subsequent full application of the IVIVC.
Estimation of prediction error externally:  The second aspect relates to how well
the model predicts data when one or more additional test data sets are used that
differ from those used to define the correlation. This is appropriate in some
situations, particularly when only two formulations with different release rates are
used to develop the IVIVC model, when calculation of prediction error internally
is inconclusive, or when a narrow therapeutic index drug is studied.
The additional test data sets used for external prediction error calculation may
have several differing characteristics compared to the data sets used in IVIVC
development.  Although formulations with different release rates provide the
optimal test of an IVIVC's predictability, a formulation need not be prepared solely
for this purpose. In the absence of such a formulation, data from other types of
formulations may be considered. In each case, bioavailability data should be
available for the data set under consideration.
The following represent, in decreasing order of preference, formulations that may
be used to estimate prediction error externally:
! A formulation with a different release rate than those used in IVIVC
development. The release rate of the test formulation may be either within
or outside the range used to define the IVIVC relationship.
! A formulation with the same or similar release rate, but involving some
change in manufacture of this batch (e.g., composition, process, equipment,
manufacturing site).  
8 ! A formulation with the same or similar release rate obtained from another
batch/lot with no changes in manufacturing.
c. Pharmacologic Properties of the Drug (Therapeutic Index)
Narrow therapeutic index drugs:  If an IVIVC model is to be used in estimating
the in vivo performance of formulations of narrow therapeutic index drugs, the
model's predictability should be tested further with a data set that differs from
those data sets used to define the correlation.  In other words, the external
predictability of the correlation should be evaluated.  
Non-narrow therapeutic index drugs:  If an IVIVC model is to be used in
estimating the in vivo performance of formulations of non-narrow therapeutic
index drugs, testing the models predictability with a data set that differs from
those data sets used to define the correlation may be desirable, but is not
considered as important as for a narrow therapeutic index drug.
Note  If the classification of a drug as a narrow therapeutic index drug is
uncertain, appropriate review staff in CDER should be consulted. 
2. Methods for Evaluation of Predictability
The objective of IVIVC evaluation is to estimate the magnitude of the error in
predicting the in vivo bioavailability results from in vitro dissolution data.  This
objective should guide the choice and interpretation of evaluation methods. Any
appropriate approach related to this objective may be used for evaluation of
predictability.
Internal predictability:  All IVIVCs should be studied regarding internal
predictability. One recommended approach involves the use of the IVIVC model
to predict each formulations plasma concentration profile (or C  and/or AUC for
max
a multiple Level C IVIVC) from each respective formulations dissolution data.
This is performed for each formulation used to develop the IVIVC model. The
predicted bioavailability is then compared to the observed bioavailability for each
formulation and a determination of prediction error is made.
Criteria
! Average absolute percent prediction error (% PE) of 10% or less for C
max
and AUC establishes the predictability of the IVIVC.  In addition, the %
PE for each formulation should not exceed 15%.
9 ! If these criteria are not met, that is, if the internal predictability of the
IVIVC is inconclusive, evaluation of external predictability of the IVIVC
should be performed as a final determination of the ability of the IVIVC to
be used as a surrogate for bioequivalence.
External predictability:  Most important when using an IVIVC as a surrogate for
bioequivalence is confidence that the IVIVC can predict in vivo performance of
subsequent lots of the drug product. Therefore, it may be important to establish
the external predictability of the IVIVC. This involves using the IVIVC to predict
the in vivo performance for a formulation with known bioavailability that was not
used in developing the IVIVC model.  
Criteria
! % PE of 10% or less for C  and AUC establishes the external
max
predictability of an IVIVC.
! % PE between 10 - 20% indicates inconclusive predictability and the need
for further study using additional data sets. Results of estimation of PE
from all such data sets should be evaluated for consistency of predictability. 
! % PE greater than 20% generally indicates inadequate predictability, unless
otherwise justified.
With the exception of narrow therapeutic index drugs, the external
predictability step in the IVIVC evaluation process may be omitted if the
evaluation of internal predictability indicates acceptable % PE.  However,
when the evaluation of internal predictability is inconclusive, evaluation of
external predictability is recommended.
VI. DEVELOPMENT AND EVALUATION OF A LEVEL C IN VITRO/IN VIVO
CORRELATION
A single point Level C correlation allows a dissolution specification to be set at the specified time
point. While the information may be useful in formulation development, waiver of an in vivo
bioequivalence study (biowaiver) is generally not possible if only a single point correlation is
available. A multiple point Level C correlation may be used to justify a biowaiver, provided that
the correlation has been established over the entire dissolution profile with one or more
pharmacokinetic parameters of interest. This could be achieved by correlating the amount
dissolved at various time points with C , AUC, or any other suitable parameter. A relationship
max
should be demonstrated at each time point with the same parameter such that the effect on the in
vivo performance of any change in dissolution can be assessed. If such a multiple Level C
10 correlation is achievable, then the development of a Level A correlation is likely. A multiple Level
C correlation should be based on at least three dissolution time points covering the early, middle,
and late stages of the dissolution profile. The recommendations for assessing the predictability of
Level C correlations will depend on the type of application for which the correlation is to be used.
These methods and criteria are the same as those for a Level A correlation (see Section V B2).
VII. APPLICATIONS OF AN IVIVC
In vitro dissolution testing is important for (1) providing process control and quality assurance;
(2) determining stable release characteristics of the product over time; and (3) facilitating certain
regulatory determinations (e.g., absence of effect of minor formulation changes or of change in
manufacturing site on performance).  In certain cases, especially for ER formulations, the
dissolution test can serve not only as a quality control for  the manufacturing process but also as
an indicator of how the formulation will perform in vivo. Thus, a main objective of developing
and evaluating an IVIVC is to establish the dissolution test as a surrogate for human
bioequivalence studies, which may reduce the number of bioequivalence studies performed during
the initial approval process as well as with certain scale-up and postapproval changes.  However,
for the applications outlined below, the adequacy of the in vitro dissolution method to act as a
surrogate for in vivo testing should be shown through an IVIVC for which predictability has been
established.
A. Biowaivers for Changes in the Manufacturing of a Drug Product
1. Category 1:  Biowaivers Without an IVIVC
For formulations consisting of beads in capsules, with the only difference between
strengths being the number of beads, approval of lower strengths without an
IVIVC is possible, provided bioavailability data are available for the highest
strength.
Where the guidance for industry SUPAC-MR: Modified Release Solid Oral
Dosage Forms; Scale-Up and Postapproval changes:  Chemistry, Manufacturing,
and Controls, In Vitro Dissolution Testing, and In Vivo Bioequivalence
Documentation recommends a biostudy, biowaivers for the same changes made on
lower strengths are possible without an IVIVC if  (1) all strengths are
compositionally proportional or qualitatively the same, (2) in vitro dissolution
profiles of all strengths are similar, (3) all strengths have the same release
mechanism, (4) bioequivalence has been demonstrated on the highest strength
(comparing changed and unchanged drug product), and (5) dose proportionality
has been demonstrated for this ER drug product. In the last circumstance (5),
documentation of dose proportionality may not be necessary if bioequivalence has
been demonstrated on the highest and lowest strengths of the drug product,
11 comparing changed and unchanged drug product for both strengths, as
recommended in SUPAC-MR.  
For the above situations, waivers can be granted without an IVIVC if dissolution
data are submitted in the application/compendial medium and in three other media
(e.g., water, 0.1N HCl, and USP buffer at pH 6.8, comparing the drug product
after the change to the drug product before the change).
Biowaivers, as defined in SUPAC-MR, that do not necessitate either
bioequivalence testing or an IVIVC will likely be granted in preapproval situations
for both narrow and non-narrow therapeutic index ER drug products if dissolution
data, as described in SUPAC-MR, are submitted. 
Comparison of dissolution profiles:  Dissolution profiles can be compared using
model independent or model dependent methods. A model independent approach
using a similarity factor, and comparison criteria are described in SUPAC-MR. 
2. Category 2: Biowaivers Using an IVIVC:  Non-Narrow Therapeutic Index
Drugs 
a. Two Formulations/Release Rates
A biowaiver will likely be granted for an ER drug product using an IVIVC
developed with two formulations/release rates for (1) Level 3
manufacturing site changes as defined in SUPAC-MR; (2) Level 3
nonrelease controlling excipient changes as defined in SUPAC-MR, with
the exception of complete removal or replacement of excipients (see
below). 
                                           
b. Three Formulations/Release Rates
A biowaiver will likely be granted for an ER drug product using an IVIVC
developed with three formulations/release rates (or developed with two
formulations/release rates with establishment of external predictability) for
(1) Level 3 process changes as defined in SUPAC-MR; (2) complete
removal of or replacement of nonrelease controlling excipients as defined in
SUPAC-MR; and (3) Level 3 changes in the release controlling excipients
as defined in SUPAC-MR.
c. Biowaivers for Lower Strengths
If an IVIVC is developed with the highest strength, waivers for changes
made on the highest strength and any lower strengths may be granted if
12 these strengths are compositionally proportional or qualitatively the same,
the in vitro dissolution profiles of all the strengths are similar, and all
strengths have the same release mechanism.
d. Approval of New Strengths
This biowaiver is applicable to strengths lower than the highest strength,
within the dosing range that has been established to be safe and effective, if
the new strengths are compositionally proportional or qualitatively the
same; have the same release mechanism; have similar in vitro dissolution
profiles; and are manufactured using the same type of equipment and the
same process at the same site as other strengths that have bioavailability
data available.
 
For generic products to qualify for this biowaiver, one of the following
situations should exist:
 
! Bioequivalence has been established for all strengths of the
reference listed product.
 
! Dose proportionality has been established for the reference listed
product, and all reference product strengths are compositionally 
proportional or qualitatively the same, have the same release
mechanism, and the in vitro dissolution profiles of all strengths are
similar.
 
!! Bioequivalence is established between the generic product and the
reference listed product at the highest and lowest strengths and, for
the reference listed product, all strengths are compositionally
proportional or qualitatively the same, have the same release
mechanism, and the in vitro dissolution profiles are similar.
Obtaining category 2d biowaivers:  The difference in predicted means of
C  and AUC should be no more than 10%, based on dissolution profiles
max
of the highest strength and the lower strength product.
e. Changes in Release Controlling Excipients
Changes in release controlling excipients in the formulation should be
within the range of release controlling excipients of the established
correlation.
13 f. Obtaining Category 2a, 2b, and 2c Biowaivers:
The difference in predicted means of C  and AUC should be no more than
max
20% from that of the reference product and, where appropriate, the new
formulation should meet the application/compendial dissolution
specifications.
3.  Category 3: Biowaivers Using an IVIVC: Narrow Therapeutic Index
Drugs
If external predictability of an IVIVC is established, the following waivers
will likely be granted if at least two formulations/release rates have been
studied for the development of the IVIVC.
a. Situations in Which Biowaivers May Be Granted
A biowaiver will likely be granted for an ER drug product using an IVIVC
for (1) Level 3 process changes as defined in SUPAC-MR; (2) complete
removal of or replacement of non-release controlling excipients as defined
in SUPAC-MR; and (3) Level 3 changes in the release controlling
excipients as defined in SUPAC-MR. 
b. Biowaivers for Lower Strengths
If an IVIVC is developed with the highest strength, waivers for changes
made on the highest strength and any lower strengths may be granted, if
these strengths are compositionally proportional or qualitatively the same,
the in vitro dissolution profiles of all the strengths are similar, and all
strengths have the same release mechanism.
c. Approval of New Strengths
This biowaiver is applicable to strengths lower than the highest strength,
within the dosing range that has been established to be safe and effective,
provided that the new strengths are compositionally proportional or
qualitatively the same, have the same release mechanism, have similar in
vitro dissolution profiles, and are manufactured using the same type of
equipment, and the same process at the same site as other strengths that
have bioavailability data available.
 
For generic products to qualify for this biowaiver, one of the following
situations should exist:
 
14 ! Bioequivalence has been established for all strengths of the
reference listed product.
! Dose proportionality has been established for the reference listed
product, all reference product strengths are compositionally
proportional or qualitatively the same and have the same release
mechanism, and the in vitro dissolution profiles of all strengths are
similar.
 
! Bioequivalence is established between the generic product and the
reference listed product at the highest and lowest strengths and, for
the reference listed product, all strengths are compositionally
proportional or qualitatively the same and have the same release
mechanism, and the in vitro dissolution profiles are similar.
Obtaining category 3c biowaivers:  The difference in predicted means of
C  and AUC should be no more than 10%, based on dissolution profiles
max
of the highest strength and the lower strength product.
d. Changes in Release Controlling Excipients
! Changes in release controlling excipients in the formulation should
be within the range of release controlling excipients of the
established correlation.  
e. Obtaining Category 3a and 3b Biowaivers:
The difference in predicted means of C  and AUC should be no more than
max
20% from that of the reference product and, where appropriate, the new
formulation meets the application/compendial dissolution specifications.
4. Category 4: Biowaivers When In Vitro Dissolution Is Independent of
Dissolution Test Conditions
Situations in which biowaivers are likely to be granted for both narrow and
non-narrow therapeutic index drugs:
a. Category 2 and Category 3 biowaivers are likely to be granted with
an IVIVC established with one formulation/release rate. 
Biowaivers may be granted if dissolution data are submitted in
application/compendial medium and in three other media (e.g., water, 0.1 N
HCl, USP buffer at pH 6.8) and the following conditions apply:
15 ! In vitro dissolution should be shown to be independent of
dissolution test conditions after change is made in drug product
manufacturing.  
! Comparison of dissolution profiles
 
Dissolution profiles can be compared using model independent or model
dependent methods. A model independent approach using a similarity
factor and comparison criteria is described in SUPAC-MR. 
b. Obtaining Category 4 Biowaivers
The difference in predicted means of C  and AUC should be no more than
max
20% from that of the reference product and, where appropriate, the new
formulation should meet the application/compendial dissolution
specifications.
5.  Category 5:  Situations for which an IVIVC Is Not Recommended
a. Approval of a new formulation of an approved ER drug product
when the new formulation has a different release mechanism.  
b. Approval of a dosage strength higher or lower than the doses that
have been shown to be safe and effective in clinical trials.  
   c. Approval of another sponsors ER product even with the same
release controlling mechanism.  
d. Approval of a formulation change involving a nonrelease
controlling excipient in the drug product that may significantly
affect drug absorption.
B. Setting Dissolution Specifications
In vitro dissolution specifications should generally be based on the performance of the
clinical/bioavailability lots. These specifications may sometimes be widened so that  scale-
up lots, as well as stability lots, meet the specifications associated with the
clinical/bioavailability lots. This approach is based on the use of the in vitro dissolution test
as a quality control test without any in vivo significance, even though in certain cases
(e.g., ER formulations), the rate limiting step in the absorption of the drug is the
dissolution of the drug from the formulation.  An IVIVC adds in vivo relevance to in vitro
dissolution specifications, beyond batch-to-batch quality control.  In this approach, the in
vitro dissolution test becomes a meaningful predictor of in vivo performance of the 
16 formulation, and dissolution specifications may be used to minimize the possibility of
releasing lots that would be different in in vivo performance.       
                   
1. Setting Dissolution Specifications Without an IVIVC
! The recommended range at any dissolution time point specification is 
10% deviation from the mean dissolution profile obtained from the
clinical/bioavailability lots.
! In certain cases, reasonable deviations from the  10 % range can be
accepted provided that the range at any time point does not exceed 25%.
Specifications greater than 25% may be acceptable based on evidence that
lots (side batches) with mean dissolution profiles that are allowed by the
upper and lower limit of the specifications are bioequivalent.
! Specifications should be established on clinical/bioavailability lots. 
Widening specifications based on scale-up, stability, or other lots for which
bioavailability data are unavailable is not recommended.
! A minimum of three time points is recommended to set the specifications.
These time points should cover the early, middle, and late stages of the
dissolution profile. The last time point should be the time point where at
least 80% of drug has dissolved. If the maximum amount dissolved is less
than 80%, the last time point should be the time when the plateau of the
dissolution profile has been reached.
! Specifications should be established based on average dissolution data for
each lot under study, equivalent to USP Stage 2 testing. Specifications
allow that all lots to pass at Stage 1 of testing may result in lots with less
than optimal in vivo performance passing these specifications at USP Stage
2 or Stage 3.
! USP acceptance criteria for dissolution testing are recommended unless
alternate acceptance criteria are specified in the ANDA/NDA.  
2. Setting Dissolution Specifications Where an IVIVC Has Been Established
Optimally, specifications should be established such that all lots that have
dissolution profiles within the upper and lower limits of the specifications are
bioequivalent. Less optimally but still possible, lots exhibiting dissolution profiles
at the upper and lower dissolution limits should be bioequivalent to the
clinical/bioavailability lots or to an appropriate reference standard. 
17 a. Level A Correlation Established
! Specifications should be established based on average data.
! A minimum of three time points is recommended to establish the
specifications. These time points should cover the early, middle and
late stages of the dissolution profile. The last time point should be
the time point where at least 80% of drug has dissolved. If the
maximum amount dissolved is less than 80%, then the last time
point should be the time where the plateau of the dissolution profile
has been reached.
! Calculate the plasma concentration time profile using convolution
techniques or other appropriate modeling techniques and determine
whether the lots with the fastest and slowest release  rates that are
allowed by the dissolution specifications result in a maximal
difference of 20% in the predicted C  and AUC.
max
! An established IVIVC may allow setting wider dissolution
specifications. This would be dependent on the predictions of the
IVIVC (i.e., 20% differences in the predicted C   and AUC).
max
! USP acceptance criteria for dissolution testing are recommended
unless alternate acceptance criteria are specified in the
ANDA/NDA.
b. Multiple Level C Correlation Established
! If a multiple point Level C correlation has been established,
establish the specifications at each time point such that there is a
maximal difference of 20% in the predicted C and AUC. 
max 
! Additionally, the last time point should be the time point where at
least 80% of drug has dissolved.
c. Level C Correlation Based on Single Time Point Established
This one time point may be used to establish the specification such that
there is not more than a 20% difference in the predicted AUC and C . At
max 
other time points, the maximum recommended range at any dissolution
time point specification should be  10% of label claim deviation from the
mean dissolution profile obtained from the clinical/bioavailability lots.
Reasonable deviations from  10% may be acceptable if the range at any
time point does not exceed 25%.
18  
3. Setting Specifications Based on Release Rate
If the release characteristics of the formulation can be described by a zero-order
process for some period of time (e.g., 5%/hr from 4 to 12 hours), and the
dissolution profile appears to fit a linear function for that period of time, a release
rate specification may be established to describe the dissolution characteristics of
that formulation. A release rate specification may be an addition to the
specifications established on the cumulative amount dissolved at the selected time
points. Alternatively, a release the rate specification may be the only specification
except for the specification for time when at least 80% of drug has dissolved.
19 REFERENCES
1. Gillespie, W. R., Office of Clinical Pharmacology and Biopharmaceutics, FDA,
"Convolution-Based Approaches for In Vivo-In Vitro Correlation Modeling."
2. FDA, September 1997, Guidance for Industry: SUPAC-MR: Modified Release Solid Oral
Dosage Forms; Scale-Up and Post-Approval Changes: Chemistry, Manufacturing and
Controls, In Vitro Dissolution Testing, and In Vivo Bioequivalence Documentation.          
            
3. Moore, J. W., and H. H. Flanner, November 1994, "Mathematical Comparison of Curves
with an Emphasis on Dissolution Profiles," presented at the AAPS National Meeting,
Personal Communication from AAI Inc., Wilmington, NC 28405.  
4. Skelly, J. P., et al., 1987, "Report of the Workshop on CR Dosage Forms: Issues and
Controversies," Pharmaceutical Research, 4(1):75-78.
5. United States Pharmacopeial Convention, Inc., July 1988, "In Vitro-In Vivo Correlation
for Extended Release Oral Dosage Forms," Pharmacopeial Forum Stimuli Article,  4160-
4161.
6. Skelly, J. P., et al., September 1990, "Report of Workshop on In Vitro and In Vivo
Testing and Correlation for Oral Controlled/Modified-Release Dosage Forms," Journal of
Pharmaceutical Sciences, 79(9):849-854.
7. United States Pharmacopeial Convention, Inc., "In Vitro In Vivo Evaluation of Dosage
Forms", USP XXIII<1088>, 1927-1929.
8. Skelly, J. P., et al., 1993, Workshop II Report "Scale-up of Oral Extended Release
Dosage Forms," Pharmaceutical Research, 10(12):1800-1805.
20 DEFINITION OF TERMS
Batch: A specific quantity of a drug or other material produced according to a single
manufacturing order during the same cycle of manufacture and intended to have uniform character
and quality, within specified limits (21 CFR 210.3(b)(2)).  
Batch formula (composition): A complete list of the ingredients and their amounts to be used
for the manufacture of a representative batch of the drug product. All ingredients should be
included in the batch formula whether or not they remain in the finished product (Guideline for
Submitting Documentation for the Manufacture of and Controls for Drug Products, FDA,
February 1987).  
Bioavailability: The rate and extent to which the active drug ingredient or therapeutic moiety is
absorbed from a drug product and becomes available at the site of drug action (21 CFR 320.1(a)). 
Biobatch: A lot of drug product formulated for purposes of pharmacokinetic evaluation in a
bioavailability/bioequivalency study. This lot should be 10% or greater than the proposed
commercial production batch or at least 100,000 units, whichever is greater. 
Bioequivalent drug products: Pharmaceutical equivalents or pharmaceutical alternatives whose
rate and extent of absorption do not show a significant difference when administered at the same
molar dose of the therapeutic moiety under similar experimental conditions, either single dose or
multiple dose. Some pharmaceutical equivalents or pharmaceutical alternatives may be equivalent
in the extent of their absorption but not in their rate of absorption and yet may be considered
bioequivalent because such differences in the rate of absorption are intentional and are reflected in
the labeling, are not essential to the attainment of effective body drug concentrations on chronic
use, or are considered medically insignificant for the particular drug product studied (21 CFR
320.1(e)).  
Convolution: Prediction of plasma drug concentrations using a mathematical model based on the
convolution integral. For example, the following convolution integral equation may be used to
predict the plasma concentration (c(t)) resulting from the absorption rate time course (r ): 
abs
c(t) = I t  c (t-u)  r (u) du
0 * abs
The function c  represents the concentration time course that would result from the instantaneous
*
absorption of a unit amount of drug and can be estimated from either i.v. bolus data, oral solution,
suspension or rapidly releasing (in vivo) immediate release dosage forms.
Correlation: As used in this guidance, a relationship between in vitro dissolution rate and in vivo
input (absorption) rate.
Deconvolution: Estimation of the time course of drug input (usually in vivo absorption or
dissolution) using a mathematical model based on the convolution integral. For example, the
21 absorption rate time course (r ) that resulted in the plasma concentrations (c(t)) may be
abs
estimated by solving the following convolution integral equation for r :
abs
c(t) = I t  c (t-u)  r (u) du
0 * abs
The function c  represents the concentration time course that would result from the instantaneous
*
absorption of a unit amount of drug and is typically estimated from either i.v. bolus data, oral
solution, suspension or rapidly releasing (in vivo) immediate release dosage forms. 
Development: Establishing an in vitro/in vivo correlation.
Drug product: A finished dosage form, e.g., tablet, capsule, or solution, that contains a drug
substance, generally, but not necessarily, in association with one or more other ingredients (21
CFR 314.3(b)). 
Extended release dosage form: A dosage form that allows a reduction in dosing frequency as
compared to that presented by a conventional dosage form, e.g., a solution or an immediate
release dosage form.
Evaluation: In the context of in vitro/in vivo correlation, a broad term encompassing
experimental and statistical techniques used during development and evaluation of a correlation
which aid in determining the predictability of the correlation.
Formulation: A listing of the ingredients and composition of the dosage form.
In vitro/in vivo correlation: A predictive mathematical model describing the relationship
between an in vitro property of an extended release dosage form (usually the rate or extent of
drug dissolution or release) and a relevant in vivo response, e.g., plasma drug concentration or
amount of drug absorbed.
In vivo dissolution: The process of dissolution of drug in the gastro-intestinal tract.
In vitro release: Drug dissolution (release) from a dosage form as measured in an in vitro
dissolution apparatus.
In vivo release: In vivo dissolution of drug from a dosage form as determined by deconvolution
of data obtained from pharmacokinetic studies in humans (patients or healthy volunteers).
Level A correlation: A predictive mathematical model for the relationship between the entire in
vitro dissolution/release time course and the entire in vivo response time course, e.g., the time
course of plasma drug concentration or amount of drug absorbed.
Level B correlation: A predictive mathematical model for the relationship between summary
parameters that characterize the in vitro and in vivo time courses, e.g., models that relate the
mean in vitro dissolution time to the mean in vivo dissolution time, the mean in vitro dissolution
22 time to the mean residence time in vivo, or the in vitro dissolution rate constant to the absorption
rate constant.
Level C correlation: A predictive mathematical model of the relationship between the amount
dissolved in vitro at a particular time (or the time required for in vitro dissolution of a fixed
percent of the dose, e.g., T %)  and a summary parameter that characterizes the in vivo time
50
course (e.g., C  or AUC).
max
Lot: A batch, or a specific identified portion of a batch, having uniform character and quality
within specified limits or, in the case of a drug product produced by continuous process, a specific
identified amount produced in a unit of time or quantity in a manner that assures its having
uniform character and quality within specified limits (21 CFR 210.3(b)(10)).  
Mean absorption time: The mean time required for drug to reach systemic circulation from the
time of drug administration. This term commonly refers to the mean time involved in the in vivo
release and absorption processes as they occur in the input compartment and is estimated as MAT
= MRT -  MRT
oral  i.v.
Mean in vitro dissolution time: The mean time for the drug to dissolve under in vitro dissolution
conditions. This is calculated using the following equation:
I4(M &M(t))dt
MDT  o 4
vitro M
4
Mean in vivo dissolution time: For a solid dosage form: MDT   =  MRT   -  MRT . This
solid solid solution
reflects the mean time for drug to dissolve in vivo.
Mean residence time: The mean time that the drug resides in the body. MRT may also be the
mean transit time. MRT = AUMC/AUC.
Narrow therapeutic index drugs: Drugs having, for example, less than a two-fold difference in
the minimum toxic concentrations and the minimum effective concentrations (21 CFR 320.33 (c)).
 
Nonrelease controlling excipient (noncritical compositional variable): An inactive ingredient
in the final dosage form that does not significantly affect the release of the active drug substance
from the dosage form.
Predictability: Verification of the model's ability to describe in vivo bioavailability results from a
test set of in vitro data (external predictability) as well as from the data that was used to develop
the correlation (internal predictability).
23 Percent prediction error:
% PE = [(Observed value - Predicted value) / Observed value] x 100
Release controlling excipient (critical compositional variable): An inactive ingredient in the
final dosage form that functions primarily to extend the release of the active drug substance from
the dosage form.
Release mechanism: The process by which the drug substance is released from the dosage form.
Release rate: Amount of drug released per unit of time as defined by in vitro or in vivo testing.
Statistical moments: Parameters that describe the characteristics of the time courses of plasma
concentration (area, mean residence time, and variance of mean residence time) and of urinary
excretion rate.
24