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
i

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
 This guidance has been prepared by the Extended Release Dissolution Working Group of the 1

Biopharmaceutics Coordinating Committee (BCC) in the Center for Drug Evaluation and Research (CDER) at the Food

and Drug Administration (FDA). This guidance represents the Agency’s 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. 

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.
2

! 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
Level A correlations are the most common type of correlation developed in NDAs submitted to the FDA. 2

Level B correlations are rarely seen in NDAs; multiple Level C correlations are seen infrequently.

3

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 correlation is usually estimated by a two-stage procedure: deconvolution 2

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.
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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, Cmax, Tmax). A Level C correlation does not reflect the complete shape of the plasma

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.
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! 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:
6

! 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 
7

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 (Cmax or AUC)

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.
8

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). 
9

! 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 model’s 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 formulation’s plasma concentration profile (or Cmax and/or AUC for

a multiple Level C IVIVC) from each respective formulation’s 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 Cmax

and AUC establishes the predictability of the IVIVC. In addition, the %

PE for each formulation should not exceed 15%.
10

! 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 Cmax and AUC establishes the external

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 Cmax, AUC, or any other suitable parameter. A relationship

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
11

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,
12

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
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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

Cmax and AUC should be no more than 10%, based on dissolution profiles

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.
14

f. Obtaining Category 2a, 2b, and 2c Biowaivers:

The difference in predicted means of Cmax and AUC should be no more than

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:
15

! 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

Cmax and AUC should be no more than 10%, based on dissolution profiles

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 Cmax and AUC should be no more than

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:
16

! 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 Cmax and AUC should be no more than

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 sponsor’s 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 scaleup 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 
17

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. 
18

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 Cmax and AUC.

! 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 Cmax and AUC).

! 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 Cmax and AUC. 

! 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 Cmax . At

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%.
19

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.
20

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.
21

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) = I0 c*(t-u) rabs(u) du t

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
22

absorption rate time course (rabs) that resulted in the plasma concentrations (c(t)) may be

estimated by solving the following convolution integral equation for r : abs

c(t) = I0 c*(t-u) rabs(u) du t

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
MDTvitro'

I

4

o

(M4&M(t))dt

M4

23

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., T50%) and a summary parameter that characterizes the in vivo time

course (e.g., Cmax or AUC).

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

= MRToral - MRTi.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:

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).
24

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.