Guideline for Industry
Dose-Response Information
to Support Drug
Registration
ICH-E4
November 1994 TABLE OF CONTENTS
I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
A. Purpose of Dose-Response Information . . . . . . . . . . . . . . . . . . . . . . . . . 1
B. Use of Dose-Response Information in Choosing Doses . . . . . . . . . . . . 2
C. Uses of Concentration-Response Data . . . . . . . . . . . . . . . . . . . . . . . . . 3
D. Problems with Titration Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
E. Interactions Between Dose-Response and Time . . . . . . . . . . . . . . . . . . 4
II. OBTAINING DOSE-RESPONSE INFORMATION . . . . . . . . . . . . . . . . . . . . 5
A. Dose-Response Assessment Should Be an Integral Part of Drug
Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
B. Studies in Life-Threatening Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C. Regulatory Considerations When Dose-Response Data are Imperfect . 6
D. Examining the Entire Database for Dose-Response Information . . . . . . 7
III. STUDY DESIGNS FOR ASSESSING DOSE RESPONSE . . . . . . . . . . . . . 7
A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
B. Specific Trial Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Parallel Dose-Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2. Cross-over Dose-Response . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3. Forced Titration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Optional Titration (Placebo-Controlled Titration to Endpoint) . . . 12
IV. GUIDANCE AND ADVICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
V. REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 GUIDELINE FOR INDUSTRY 1
DOSE-RESPONSE INFORMATION TO 
SUPPORT DRUG REGISTRATION
I. INTRODUCTION 
A. Purpose of Dose-Response Information
Knowledge of the relationships among dose, drug concentration drug
concentration in blood, and clinical response (effectiveness and
undesirable effects) is important for the safe and effective use of drugs in
individual patients.  This information can help identify an appropriate
starting dose, the best way to adjust dosage to the needs of a particular
patient, and a dose beyond which increases would be unlikely to provide
added benefit or would produce unacceptable side effects. 
Dose-concentration, concentration- and/or dose-response information is
used to prepare dosage and administration instructions in product
labeling.  In addition, knowledge of dose-response may provide an
economical approach to global drug development, by enabling multiple
regulatory agencies to make approval decisions from a common
1This guideline was developed within the Expert Working Group (Efficacy) of the
International Conference on Harmonisation of Technical Requirements for the
Registration of Pharmaceuticals for Human Use (ICH) and has been subject to
consultation by the regulatory parties, in accordance with the ICH process.  This
document has been endorsed by the ICH Steering Committee at  Step 4 of the ICH
process, March 10, 1994.  At  Step 4 of the process, the final draft is recommended for
adoption to the regulatory bodies of the European Union, Japan and the USA.  This
guideline was published in the  Federal Register on November 9, 1994 (59 FR 55972)
and is applicable to both drug and biological products.  In the past, guidelines have
generally been issued under  10.90(b) [21 CFR 10.90(b)], which provides for the use
of guidelines to state procedures or standards of general applicability that are not legal
requirements but that are acceptable to FDA.  The agency is now in the process of
revising 10.90(b).  Therefore, this guideline is not being issued under the authority of
10.90(b), and it does not create or confer any rights, privileges or benefits for or on
any person, nor does it operate to bind FDA in any way.  For additional copies of this
guideline contact the Executive Secretariat Staff, HFD-8, Center for Drug Evaluation
and Research, 7500 Standish Place, Rockville, MD, 20855, 301-594-1012.  An
electronic version of this guideline is also available via Internet by connecting to the
CDER FTP server (CDVS2.CDER.FDA.GOV) using the FTP protocol. database.  
Historically, drugs have often been initially marketed at what were later
recognized as excessive doses (i.e., doses well onto the plateau of the
dose-response curve for the desired effect), sometimes with adverse
consequences (e.g., hypokalemia and other metabolic disturbances with
thiazide-type diuretics in hypertension).  This situation has been improved
by attempts to find the smallest dose with a discernible useful effect or a
maximum dose beyond which no further beneficial effect is seen, but
practical study designs do not exist to allow for precise determination of
these doses.  Further, expanding knowledge indicates that the concepts
of minimum effective dose and maximum useful dose do not adequately
account for individual differences and do not allow a comparison, at
various doses, of both beneficial and undesirable effects.  Any given dose
provides a mixture of desirable and undesirable effects, with no single
dose necessarily optimal for all patients.
B. Use of Dose-Response Information in Choosing Doses
What is most helpful in choosing the starting dose of a drug is knowing
the shape and location of the population (group) average dose-response
curve for both desirable and undesirable effects.  Selection of dose is
best based on that information, together with a judgment about the
relative importance of desirable and undesirable effects.  For example, a
relatively high starting dose (on or near the plateau of the effectiveness
dose-response curve) might be recommended for a drug with a large
demonstrated separation between its useful and undesirable dose ranges
or where a rapidly evolving disease process demands rapid effective
intervention.  A high starting dose, however, might be a poor choice for a
drug with a small demonstrated separation between its useful and
undesirable dose ranges.  In these cases, the recommended starting
dose might best be a low dose exhibiting a clinically important effect in
even a fraction of the patient population, with the intent to titrate the dose
upwards as long as the drug is well tolerated.  Choice of a starting dose
might also be affected by potential intersubject variability in
pharmacodynamic response to a given blood concentration level, or by
anticipated intersubject pharmacokinetic differences, such as could arise
from nonlinear kinetics, metabolic polymorphism, or a high potential for
pharmacokinetic drug-drug interactions.  In these cases, a lower starting
dose would protect patients who obtain higher blood concentrations.  It is
entirely possible that different physicians and even different regulatory
authorities, looking at the same data, would make different choices as to
the appropriate starting doses, dose-titration steps, and maximum
recommended dose, based on different perceptions of risk/benefit relationships.  Valid dose response data allow the use of such judgment.  
In adjusting the dose in an individual patient after observing the response
to an initial dose, what would be most helpful is knowledge of the shape
of individual dose-response curves, which is usually not the same as the
population (group) average dose-response curve.  Study designs that
allow estimation of individual dose-response curves could therefore be
useful in guiding titration, although experience with such designs and
their analysis is very limited.
 
In utilizing dose-response information, it is important to identify, to the
extent possible, factors that lead to differences in pharmacokinetics of
drugs among individuals, including demographic factors (e.g., age,
gender, race), other diseases (e.g., renal or hepatic failure), diet,
concurrent therapies, or individual characteristics (e.g., weight, body
habitus, other drugs, metabolic differences).
 
C. Uses of Concentration-Response Data 
Where a drug can be safely and effectively given only with blood
concentration monitoring, the value of concentration-response information
is obvious.  In other cases, an established concentration-response
relationship is often not needed, but may be useful:  (1) For ascertaining
the magnitude of the clinical consequences of pharmacokinetic
differences, such as those due to drug-disease (e.g., renal failure) or
drug-drug interactions; or (2) for assessing the effects of the altered
pharmacokinetics of new dosage forms (e.g., controlled release
formulation) or new dosage regimens without need for additional clinical
trial data, where such assessment is permitted by regional regulations. 
Prospective randomized concentration-response studies are obviously
critical to defining concentration monitoring therapeutic "windows," but
are also useful when pharmacokinetic variability among patients is great;
in that case, a concentration-response relationship may in principle be
discerned in a prospective study with a smaller number of subjects than
could the dose-response relationship in a standard dose-response study. 
Note that collection of concentration-response information does not imply
that therapeutic blood level monitoring will be needed to administer the
drug properly.  Concentration-response relationships can be translated
into dose-response information.  Concentration-response information can
also allow selection of doses (based on the range of concentrations they
will achieve) most likely to lead to a satisfactory response.  Alternatively,
if the relationships between concentration and observed effects (e.g., an
undesirable or desirable pharmacologic effect) are defined, the drug can
be titrated according to patient response without the need for further blood level monitoring.  
D. Problems With Titration Designs
A study design widely used to demonstrate effectiveness utilizes dose
titration to some effectiveness or safety endpoint.  Such titration designs,
without careful analysis, are usually not informative about dose-response
relationships.  In many studies, there is a tendency to spontaneous
improvement over time that is not easily distinguishable from an
increased response to higher doses or cumulative drug exposure.  This
leads to a tendency to choose, as a recommended dose, the highest
dose used in such studies that was reasonably well tolerated. 
Historically, this approach has often led to a dose that was well in excess
of what was really necessary, resulting in increased undesirable effects,
e.g., to high-dose diuretics used for hypertension.  In some cases,
notably where an early answer is essential, the
titration-to-highest-tolerable-dose approach is acceptable, because it
often requires a minimum number of patients.  For example, the first
marketing of zidovudine (AZT) for treatment of people with acquired
immune deficiency syndrome (AlDS) was based on studies at a high
dose; later studies showed that lower doses were as effective and far
better tolerated.  The urgent need for the first effective anti-HIV (human
immunodeficiency virus) treatment made the absence of dose-response
information at the time of approval reasonable (with the condition that
more data were to be obtained after marketing), but in less urgent cases
this approach is discouraged. 
E. Interactions Between Dose-Response and Time
The choice of the size of an individual dose is often intertwined with the
frequency of dosing.  In general, when the dose interval is long compared
to the half-life of the drug, attention should be directed to the
pharmacodynamic basis for the chosen dosing interval.  For example,
there might be a comparison of the long dose interval regimen with the
same dose in a more divided regimen, looking, where this is feasible, for
persistence of desired effect throughout the dose interval and for adverse
effects associated with blood level peaks.  Within a single dose interval,
the dose-response relationships at peak and trough blood levels may
differ and the relationship could depend on the dose interval chosen.
Dose-response studies should take time into account in a variety of other
ways.  The study period at a given dose should be long enough for the
full effect to be realized, whether delay is the result of pharmacokinetic or
pharmacodynamic factors.  The dose-response may also be different for morning versus evening dosing.  Similarly, the dose-response
relationship during early dosing may not be the same as in the
subsequent maintenance dosing period.  Responses could also be
related to cumulative dose, rather than daily dose, to duration of exposure
(e.g., tachyphylaxis, tolerance, or hysteresis) or to the relationships of
dosing to meals.
II. OBTAINING DOSE-RESPONSE INFORMATION
A. Dose-Response Assessment Should Be an Integral Part of Drug
Development 
Assessment of dose-response should be an integral component of drug
development with studies designed to assess dose-response an inherent
part of establishing the safety and effectiveness of the drug.  If
development of dose-response information is built into the development
process it can usually be accomplished with no loss of time and minimal
extra effort compared to development plans that ignore dose-response.
 
B. Studies in Life-Threatening Diseases
 
In particular therapeutic areas, different therapeutic and investigational
behaviors have evolved; these affect the kinds of studies typically carried
out.  Parallel dose-response study designs with placebo, or
placebo-controlled titration study designs (very effective designs, typically
used in studies of angina, depression, hypertension, etc.) would not be
acceptable in the study of some conditions, such as life-threatening
infections or potentially curable tumors, at least if there were effective
treatments known.  Moreover, because in those therapeutic areas
considerable toxicity could be accepted, relatively high doses of drugs
are usually chosen to achieve the greatest possible beneficial effect
rapidly.  This approach may lead to recommended doses that deprive
some patients of the potential benefit of a drug by inducing toxicity that
leads to cessation of therapy.  On the other hand, use of low, possibly
subeffective, doses, or of titration to desired effect may be unacceptable,
as an initial failure in these cases may represent an opportunity for cure
forever lost.
Nonetheless, even for life-threatening diseases, drug developers should
always be weighing the gains and disadvantages of varying regimens
and considering how best to choose dose, dose-interval and
dose-escalation steps.  Even in indications involving life-threatening
diseases, the highest tolerated dose, or the dose with the largest effect
on a surrogate marker will not always be the optimal dose.  Where only a single dose is studied, blood concentration data, which will almost always
show considerable individual variability due to pharmacokinetic
differences, may retrospectively give clues to possible
concentration-response relationships.
Use of just a single dose has been typical of large-scale intervention
studies (e.g., post-myocardial infarction studies) because of the large
sample sizes needed.  In planning an intervention study, the potential
advantages of studying more than a single dose should be considered. 
In some cases, it may be possible to simplify the study by collecting less
information on each patient, allowing study of a larger population treated
with several doses without significant increase in costs.
 
C. Regulatory Considerations When Dose-Response Data Are Imperfect 
Even well-laid plans are not invariably successful.  An otherwise
well-designed dose-response study may have utilized doses that were
too high, or too close together, so that all appear equivalent (albeit
superior to placebo).  In that case, there is the possibility that the lowest
dose studied is still greater than needed to exert the drug's maximum
effect.  Nonetheless, an acceptable balance of observed undesired
effects and beneficial effects and beneficial effects might make marketing
at one of the doses studied reasonable.  This decision would be easiest,
of course, if the drug had special value, but even if it did not, in light of the
studies that partly defined the proper dose range, further dose-finding
might be pursued in the postmarketing period.  Similarly, although
seeking dose response data should be a goal of every development
program, approval based on data from studies using a fixed single dose
or a defined dose range (but without valid dose response information)
might be appropriate where benefit from a new therapy in treating or
preventing a serious disease is clear.
D. Examining the Entire Database for Dose-Response Information
In addition to seeking dose-response information from studies specifically
designed to provide it, the entire database should be examined
intensively for possible dose-response effects.  The limitations imposed
by certain study design features should, of course, be appreciated.  For
example, many studies titrate the dose upward for safety reasons.  As
most side effects of drugs occur early and may disappear with continued
treatment, this can result in a spuriously higher rate of undesirable effects
at the lower doses.  Similarly, in studies where patients are titrated to a
desired response, those patients relatively unresponsive to the drug are
more likely to receive the higher dose, giving an apparent, but misleading, inverted "U-shaped" dose-response curve.  Despite such limitations,
clinical data from all sources should be analyzed for dose-related effects
using multivariate multivariate or other approaches, even if the analyses
can yield principally hypotheses, not definitive conclusions.  For example,
an inverse relation of effect to weight or creatinine clearance could reflect
a dose-related covariate relationship.  If pharmacokinetic screening
(obtaining a small number of steady-state blood concentration
measurements in most Phase 2 and Phase 3 study patients) is carried
out, or if other approaches to obtaining drug concentrations during trials
are used, a relation of effects (desirable or undesirable) to blood
concentrations may be discerned.  The relationship may by itself be a
persuasive description of concentration-response or may suggest further
study.
III. STUDY DESIGNS FOR ASSESSING DOSE RESPONSE
 
A. General
The choice of study design and study population in dose-response trials
will depend on the phase of development, the therapeutic indication under
investigation, and the severity of the disease in the patient population of
interest.  For example, the lack of appropriate salvage therapy for
life-threatening or serious conditions with irreversible outcomes may
ethically preclude conduct of studies at doses below the maximum
tolerated dose.  A homogeneous patient population will generally allow
achievement of study objectives with small numbers of subjects given
each treatment.  On the other hand, larger, more diverse populations
allow detection of potentially important covariate effects.  
In general, useful dose-response information is best obtained from trials
specifically designed to compare several doses.  A comparison of results
from two or more controlled trials with single fixed doses might
sometimes be informative, e.g., if control groups were similar, although
even in that case, the many across-study differences that occur in
separate trials usually make this approach unsatisfactory.  It is also
possible in some cases to derive, retrospectively, blood
concentration-response relationships from the variable concentrations
attained in a fixed-dose trial.  While these analyses are potentially
confounded by disease severity or other patient factors, the information
can be useful and can guide subsequent studies.  Conducting
dose-response studies at an early stage of clinical development may
reduce the number of failed Phase 3 trials, speeding the drug
development process and conserving development resources. Pharmacokinetic information can be used to choose doses that ensure
adequate spread of attained concentration-response values and diminish
or eliminate overlap between attained concentrations in dose-response
trials.  For drugs with high pharmacokinetic variability, a greater spread of
doses could be chosen. Alternatively, the dosing groups could be
individualized by adjusting for pharmacokinetic covariates (e.g.,
correction for weight, lean body mass, or renal function) or a
concentration-controlled study could be carried out.
 
As a practical matter, valid dose-response data can be obtained more
readily when the response is measured by a continuous or categorical
variable, is relatively rapidly obtained after therapy is started, and is
rapidly dissipated after therapy is stopped (e.g., blood pressure,
analgesia, bronchodilation).  In this case, a wider range of study designs
can be used and relatively small, simple studies can give useful
information.  Placebo-controlled individual subject titration designs typical
of many early drug development studies, for example, properly conducted
and analyzed (quantitative analysis that models and estimates the
population and individual dose-response relationships), can give
guidance for more definitive parallel, fixed-dose, dose-response studies
or may be definitive on their own.
In contrast, when the study endpoint or adverse effect is delayed,
persistent, or irreversible (e.g., stroke or heart prevention, asthma
prophylaxis, arthritis treatments with late onset response, survival in
cancer, treatment of depression), titration and simultaneous assessment
of response is usually not possible, and the parallel dose-response study
is usually needed.  The parallel dose-response study also offers
protection against missing an effective dose because of an inverted
"U-shaped" (umbrella or bell-shaped) dose-response curve, where higher
doses are less effective than lower doses, a response that can occur, for
example, with mixed agonist-antagonists.  
Trials intended to evaluate dose- or concentration-response should be
well-controlled, using randomization and blinding (unless blinding is
unnecessary or impossible) to assure comparability of treatment groups
and to minimize potential patient, investigator, and analyst bias, and
should be of adequate size.
It is important to choose as wide a range of doses as is compatible with
practicality and patient safety to discern clinically meaningful differences. 
This is especially important where there are no pharmacologic or
plausible surrogate endpoints to give initial guidance as to dose. 
 
B. Specific Trial Designs A number of specific study designs can be used to assess
dose-response.  The same approaches can also be used to measure
concentration-response relationships.  Although not intended to be an
exhaustive list, the following approaches have been shown to be useful
ways of deriving valid dose-response information.  Some designs outlined
in this guidance are better established than others, but all are worthy of
consideration.  These designs can be applied to the study of established
clinical endpoints or surrogate endpoints.
1. Parallel Dose-Response
Randomization to several fixed-dose groups (the randomized
parallel dose-response study) is simple in concept and is a design
that has had extensive use and considerable success.  The fixed
dose is the final or maintenance dose; patients may be placed
immediately on that dose or titrated gradually (in a scheduled
"forced" titration) to it if that seems safer.  In either case, the final
dose should be maintained for a time adequate to allow the
dose-response comparison.  Although including a placebo group in
dose-response studies is desirable, it is not theoretically necessary
in all cases; a positive slope, even without a placebo group,
provides evidence of a drug effect.  To measure the absolute size
of the drug effect, however, a placebo or comparator with very
limited effect on the endpoint of interest is usually needed. 
Moreover, because a difference between drug groups and placebo
unequivocally shows effectiveness, inclusion of a placebo group
can salvage, in part, a study that used doses that were all too high
and, therefore, showed no dose-response slope, by showing that
all doses were superior to placebo.  In principle, being able to
detect a statistically significant difference in pair-wise comparisons
between doses is not necessary if a statistically significant trend
(upward slope) across doses can be established using all the data. 
It should be demonstrated, however, that the lowest dose(s)
tested, if it is to be recommended, has a statistically significant and
clinically meaningful effect.
 
The parallel dose-response study gives group mean
(population-average) dose-response, not the distribution or shape
of individual dose-response curves.
It is all too common to discover, at the end of a parallel
dose-response study, that all doses were too high (on the plateau
of the dose-response curve), or that doses did not go high enough. 
A formally planned interim analysis (or other multi-stage design) might detect such a problem and allow study of the proper dose
range.
As with any placebo-controlled trial, it may also be useful to
include one or more doses of an active drug control.  Inclusion of
both placebo and active control groups allows assessment of
"assay sensitivity," permitting a distinction between an ineffective
drug and an "ineffective'' (null, no test) study.  Comparison of
dose-response curves for test and control drugs, not yet a
common design, may also represent a more valid and informative
comparative effectiveness/safety study than comparison of single
doses of the two agents. 
The factorial trial is a special case of the parallel dose-response
study to be considered when combination therapy is being
evaluated.  It is particularly useful when both agents are intended
to affect the same response variable (a diuretic and another
anti-hypertensive, for example), or when one drug is intended to
mitigate the side effects of the other.  These studies can show
effectiveness (a contribution of each component of the
combination) and, in addition, provide dosing information for the
drugs used alone and together.
A factorial trial employs a parallel fixed-dose design with a range of
doses of each separate drug and some or all combinations of
these doses.  The sample size need not be large enough to
distinguish single cells from each other in pair-wise comparisons
because all of the data can be used to derive dose-response
relationships for the single agents and combinations, i.e., a
dose-response surface.  These trials, therefore, can be of
moderate size.  The doses and combinations that could be
approved for marketing might not be limited to the actual doses
studied but might include doses and combinations in between
those studied.  There may be some exceptions to the ability to rely
entirely on the response surface analysis in choosing dose(s).  At
the low end of the dose range, if the doses used are lower than the
recognized effective doses of the single agents, it would ordinarily
be important to have adequate evidence that these can be
distinguished from placebo in a pair-wise comparison.  One way to
do this in the factorial study is to have the lowest dose combination
and placebo groups be somewhat larger than other groups;
another is to have a separate study of the low-dose combination. 
Also, at the high end of the dose range, it may be necessary to
confirm the contribution of each component to the overall effect.   
2. Cross-over Dose-Response
 
A randomized multiple cross-over study of different doses can be
successful if drug effect develops rapidly and patients return to
baseline conditions quickly after cessation of therapy, if responses
are not irreversible (cure, death), and if patients have reasonably
stable disease.  This design suffers, however, from the potential
problems of all cross-over studies: It can have analytic problems if
there are many treatment withdrawals; it can be quite long in
duration for an individual patient; and there is often uncertainty
about carry-over effects (longer treatment periods may minimize
this problem), baseline comparability after the first period, and
period-by-treatment interactions.  The length of the trial can be
reduced by approaches that do not require all patients to receive
each dose, such as balanced incomplete block designs.
 
The advantages of the design are that each individual receives
several different doses so that the distribution of individual
dose-response curves may be estimated, as well as the population
average curve, and that, compared to a parallel design, fewer
patients may be needed.  Also, in contrast to titration designs,
dose and time are not confounded and carry-over effects are
better assessed.
 
3. Forced Titration
 
A forced titration study, where all patients move through series of
rising doses, is similar in concept and limitations to a randomized
multiple cross-over dose-response study, except that assignment
to dose levels is ordered, not random.  If most patients complete all
doses, and if the study is controlled with a parallel placebo group,
the forced titration study allows a series of comparisons of an
entire randomized group given several doses of drug with a
concurrent placebo, just as the parallel fixed-dose trial does.  A
critical disadvantage is that, by itself, this study design cannot
distinguish response to increased dose from response to
increased time on drug therapy or a cumulative drug dosage
effect.  It is therefore an unsatisfactory design when response is
delayed, unless treatment at each dose is prolonged.  Even where
the time until development of effect is known to be short (from
other data), this design gives poor information on adverse effects,
many of which have time-dependent characteristics.  A tendency
toward spontaneous improvement, a very common circumstance, will be revealed by the placebo group, but is nonetheless a
problem for this design, as over time, the higher doses may find
little room to show an increased effect.  This design can give a
reasonable first approximation of both population-average dose
response and the distribution of individual dose-response
relationships if the cumulative (time-dependent) drug effect is
minimal and the number of treatment withdrawals is not excessive. 
Compared to a parallel dose-response study, this design may use
fewer patients, and by extending the study duration, can be used
to investigate a wide range of doses, again making it a reasonable
first study.  With a concurrent placebo group this design can
provide clear evidence of effectiveness, and may be especially
valuable in helping choose doses for a parallel dose-response
study.
4. Optional Titration (Placebo-Controlled Titration to Endpoint)
In this design, patients are titrated until they reach a
well-characterized favorable or unfavorable response, defined by
dosing rules expressed in the protocol.  This approach is most
applicable to conditions where the response is reasonably prompt
and is not an irreversible event, such as stroke or death.  A crude
analysis of such studies, e.g., comparing the effects in the
subgroups of patients titrated to various dosages, often gives a
misleading inverted "U-shaped" curve, as only poor responders
are titrated to the highest dose.  However, more sophisticated
statistical analytical approaches that correct for this occurrence, by
modeling and estimating the population and individual
dose-response relationships, appear to allow calculation of valid
dose-response information.  Experience in deriving valid
dose-response information in this fashion is still limited.  It is
important, in this design, to maintain a concurrent placebo group to
correct for spontaneous changes, investigator expectations, etc. 
Like other designs that use several doses in the same patient, this
design may use fewer patients than a parallel fixed-dose study of
similar statistical power and can provide both population average
and individual dose-response information.  The design does,
however, risk confounding of time and dose effects and would be
expected to have particular problems in finding dose-response
relationships for adverse effects.  Like the forced titration design, it
can be used to study a wide dose range and, with a concurrent
placebo group, can provide clear evidence of effectiveness.  It too
may be especially valuable as an early study to identify doses for a
definitive parallel study.  
IV. GUIDANCE AND ADVICE
1. Dose response data are desirable for almost all new chemical entities
entering the market.  These data should be derived from study designs
that are sound and scientifically based; a variety of different designs can
give valid information.  The studies should be well-controlled, using
accepted approaches to minimize bias.  In addition to carrying out formal
dose-response studies, sponsors should examine the entire database for
possible dose-response information.
2. The information obtained through targeted studies and analyses of the
entire database should be used by the sponsor to:
a. Identify a reasonable starting dose, ideally with specific
adjustments (or a firm basis for believing none is needed) for
patient size, gender, age, concomitant illness, and concomitant
therapy, reflecting an integration of what is known about
pharmacokinetic and pharmacodynamic variability.  Depending on
circumstances (the disease, the drug's toxicity), the starting dose
may range from a low dose with some useful effect to a dose that
is at or near the full-effect dose.
b. Identify reasonable, response-guided titration steps, and the
interval at which they should be taken, again with appropriate
adjustments for patient characteristics.  These steps would be
based either on the shape of the typical individual's dose-effect
dose-effect curves (for both desirable and undesirable effects), if
individual dose-response data were available, or if not, on the
shape of the population (group)-average dose-response, and the
time needed to detect a change in these effects.  It should be
noted that methodology for finding the population (group)-average
dose-response, at present, is better established than is
methodology for finding individual dose-response relationships.
c. Identify a dose, or a response (desirable or undesirable), beyond
which titration should not ordinarily be attempted because of a lack
of further benefit or an unacceptable increase in undesirable
effects.
3. It is prudent to carry out dose-ranging or concentration-response studies
early in development as well as in later stages in order to avoid failed
Phase 3 studies or accumulation of a database that consists largely of
exposures at ineffective or excessive doses.  The endpoints of studies may vary at different stages of drug development.  For example, in
studying a drug for heart failure, a pharmacodynamic endpoint might be
used early (e.g., cardiac output, pulmonary capillary wedge pressure), an
intermediate endpoint might be used later (e.g., exercise tolerance,
symptoms) and a mortality or irreversible morbidity endpoint might be the
final assessment (survival, new infarction).  It should be anticipated that
the dose response for these endpoints may be different.  Of course, the
choice of endpoints that must be studied for marketing approval will
depend on the specific situation.
4. A widely used, successful, and acceptable design, but not the only study
design for obtaining population average dose-response data, is the
randomized parallel, dose-response study with three or more dosage
levels, one of which may be zero (placebo).  From such a trial, if dose
levels are well chosen, the relationship of drug dosage, or drug
concentration, to clinical beneficial or undesirable effects can be defined.
Several dose levels are needed, at least two in addition to placebo, but in
general, study of more than the minimum number of doses is desirable. 
A single dose level of drug versus placebo allows a test of the null
hypothesis of no difference between drug and placebo, but cannot define
the dose-response relationship.  Similarly, although a linear relationship
can be derived from the response to two active doses (without placebo),
this approximation is usually not sufficiently informative.  Study designs
usually should emphasize elucidation of the dose-response function, not
individual pair-wise comparisons.  If a particular point on the curve, e.g.,
whether a certain low dose is useful, becomes an issue, it should be
studied separately.
5. Dose-response data for both beneficial and undesirable effects may
provide information that allows approval of a range of doses that
encompass an appropriate benefit-to-risk ratio.  A well-controlled
dose-response study is also a study that can serve as primary evidence
of effectiveness.
6. Regulatory agencies and drug developers should be open to new
approaches and to the concept of reasoned and well-documented
exploratory data analysis of existing or future databases in search of
dose-response data.  Agencies should also be open to the use of various
statistical and pharmacometric techniques such as Bayesian and
population methods, modeling, and pharmacokinetic- pharmacodynamic
approaches.  However, these approaches should not subvert the
requirement for dose-response data from prospective, randomized,
multi-dose-level clinical trials.  Post-hoc exploratory data analysis in search of dose-response information from databases generated to meet
other objectives will often generate new hypotheses, but will only
occasionally provide definitive assessment of dose-response
relationships.
A variety of data analytical techniques, including increased use of
retrospective population-type analyses, and novel designs (e.g.,
sequential designs) may help define the dose-response relationship.  For
example, fixed-dose designs can be reanalyzed as a continuum of dose
levels if doses are refigured on a milligram per kilogram (mg/kg) basis, or
adjusted for renal function, lean body mass, etc.  Similarly, blood levels
taken during a dose-response study may allow estimates of
concentration-response relationships.  Adjustment of drug exposure
levels might be made on the basis of reliable information on drug-taking
compliance.  In all of these cases, one should always be conscious of
confounding, i.e., the presence of a factor that alters both the refigured
dose and response or that alters both blood level and response,
compliance and response, etc.
 
7. Dose-response data should be explored for possible differences in
subsets based on demographic characteristics, such as age, gender, or
race.  To do this, it is important to know whether there are
pharmacokinetic differences among these groups, e.g., due to metabolic
differences, differences in body habitus, or composition, etc.
8. Approval decisions are based on a consideration of the totality of
information on a drug.  Although dose-response information should be
available, depending on the kind and degree of effectiveness shown,
imperfections in the database may be acceptable with the expectation
that further studies will be carried out after approval.  Thus, informative
dose-response data, like information on responses in special populations,
on long-term use, on potential  drug-drug and drug-disease interactions,
is expected, but might, in the face of a major therapeutic benefit or urgent
need, or very low levels of observed toxicity, become a deferred
requirement.
V. REFERENCE
Federal Register. Vol. 59, No. 216, Wednesday, November 9, 1994, pages
55972-55976.