Innovation in Drug Development: Adaptive Designs for Clinical Trials

Definitions, Classification, Regulatory Responses, Operational Considerations and Recommendations

By: Anastassios D. Retzios, Ph.D.*



A. Abstract 2

B.  Introduction. 3

C. Definitions. 4

D. Types of adaptive designs: 5

1.    Model-dependent/Continual Reassessment Adaptive Designs. 7

2.    Group Sequential/Sample-size Re-Estimation Designs. 8

3.    Group Sequential/Response Adaptive Designs. 10

4.    Randomization Adaptive Designs. 11

E.  Utilization of Bayesian Statistics. 11

F.  Regulatory Agencies and their Response to Clinical Study Innovations. 12

1.    The FDA’s Critical Path Initiative and Design Issues in Clinical Studies. 12

a.        The FDA’s View of Adaptive Designs. 12

b.       The FDA Guidance on Adaptive Designs. 13

2.    The EMEA initiative. 14

a.        The EMEA’s Reflection Paper on Adaptive Designs in Confirmatory Studies. 14

G. Operational Considerations. 17

H. Recommendations. 18

1.    The Planning Stage. 18

2.    The Conduct Stage. 20

3.    The Imperative of Full Documentation. 20

I.   Conclusions. 21

J.   Keywords. 22

K. References. 22


A.    Abstract

In the last decade there has been an increased interest in adaptive designs for clinical trials.  These designs allow the modification of several provisions of the clinical study protocol following an interim analysis while preserving the validity and integrity of the study.  The elements that can be modified include the sample size of the study, the type of patient enrolled, the randomization algorithm, the primary endpoint and others.  These designs promise a reduction of the attrition rate in new medical entities in development and reductions in time and money required to develop new agents.  The experience so far is limited and such claims remain to be verified.

A number of industry groups have attempted to define and promote the use of these designs.  The Pharmaceutical Research and Manufacturers of America (PhRMA) defined adaptive designs a “study designs that uses accumulated data to modify elements of the study without undermining the validity and integrity of the study”, a definition that has met with wide acceptance.

There are various classifications of these designs.  The one introduced in this paper is based on the degree of heterogeneity between parts of the study after the interim analysis.  Thus, we discern four main groups: model-dependent/continuous assessment method; group sequential/sample size re-estimation; group sequential/response adaptive and adaptive randomization designs.

The regulatory response to these designs has been surprisingly uniform in the US and Europe. The FDA and the EMEA noted the promise of these designs but also sounded a note of caution regarding several practices.  Neither of these agencies has produced a full official guidance at this stage.  Members of the FDA and the EMEA have published papers in industry journals examining aspects of these designs.  The FDA has shown elements of a draft guidance to industry/regulator forums and the EMEA has produced a reflection paper on adaptive designs used in confirmatory clinical trials.  This report examines these publications and summarizes the current regulatory approach to these designs.  It is expected that the regulatory position would evolve with the increased utilization of these designs.

There are a number of operational considerations in the application of these designs.  The potential beneficial effect of adaptations depends highly on the information derived by data collected from each patient treated in the study (in continual assessment method designs) or at the interim analysis (for group sequential designs).  Thus, it is imperative that the study management makes certain that compliance to the study is strictly enforced and that data are collected in a timely and accurate fashion.  A high number of deviations or many missing data will undermine the validity of the analysis and the quality of the decision from the small set of data at the interim.  In addition, when unblinding is required for the interim analysis, the appropriate firewalls should be in place and should be copiously documented.  It is imperative that no bias is introduced by either the sponsor or independent committees that render decisions on various study adaptations.  This paper provides certain recommendations for meeting the operational demands of these studies.

B.    Introduction

In one of my previous articles on the rate of failure in Phase 3 clinical studies,[1] certain fault lines in clinical research were examined. We discussed limitations in designs and endpoints that affect the pace of development and/or the accuracy and reliability of the collected information.   After more than four decades of modern clinical research, the limitations of our “tools” are becoming obvious, but the methods to overcome them are not. 

As can be seen in Figure 1, there has been a progressive and substantial decrease in the approval rate of new medical entities (NMEs) and hefty increases in development budgets.  These findings are not limited to the US. They are consistent throughout the area covered by major regulatory agencies.  The reasons for this trend are multiple: The limitations of clinical development tools are certainly one them and one that has been addressed previously by the author.[1] Others are related to bottlenecks in discovery (relevant animal models, biomarkers, etc.), inadequate information sharing, risk-averse funding of new companies, industry consolidation and the concentration of resources to new medical entities (NMEs) with substantial marketing potential.

Alarmed by this trend, both the FDA and EMEA have launched initiatives to jumpstart the process of innovation, as have various academic and industry forums.  These initiatives address clinical study designs among other research bottlenecks.  Thus, the renewed interest in clinical study designs referred to as “adaptive” or “flexible”.

The concept and practice of changes in clinical trial design based on accumulated information are by no means new. However, recent innovations in the manner and the extent to which these adaptations can be pursued while retaining study validity and integrity have captured the attention of many in the pharmaceutical R&D community.[2]  They have also elicited strong interest from regulatory authorities in pursuit of efforts to increase innovation in drug development.  As the utilization of these methods is still rare, it remains to be determined if adaptive designs are capable of reducing budgets, shrinking timelines and of improving attrition rates.  As we will be discussing later, there is a price to be paid for adaptability as the associated operational efforts are often very demanding.

It is important to note here that this paper is not meant to be a detailed review of adaptive clinical trial designs. A number of recent reviews provide an exceptional level of detail.[3]  Although core elements of these designs will be summarized therein,  my aim here is to broadly classify these designs in terms easily understood by all participants in pharmaceutical research,  examine their impact on associated operational activities, highlight regulatory concerns in the US and EU, and discuss their relevance in a real world environment.

C.     Definitions

Adapting clinical trials to problems encountered while patient accession and data collection is ongoing is not new.  In many cases, changes to the protocol are necessitated by a variety of factors, most notably lower than expected accession rates or difficulty in collecting specific information pertinent to the endpoints of the study.  Studies can also be stopped after planned interim analyses for achieving their efficacy goals or for futility. However, the term “adaptive clinical trial design” extends beyond these practices.

In 2006, the PhRMA, a pharmaceutical industry organization, assembled a working group to provide definitions and to examine additional issues pertaining to adaptive clinical trial designs.[4]  This group defined the term “adaptive design” as “any clinical study design that uses accumulated data to modify elements of the study without undermining the validity and integrity of the study”

The first element of the definition is not specific enough to provide any insight.  As mentioned earlier, modifications of studies (either planned or unplanned) on the basis of collected information were not unknown prior to the recent emphasis on “adaptive designs”.  Interim analyses in a group sequential methodology allowed the possibility of the “early” termination of the clinical study if efficacy had been achieved and for futility while preserving the type I error (maintaining the rate of false positives at the pre-specified level).  In fact, such designs also allowed a certain flexibility regarding the number of interim analyses.[5]  Obviously, the “adaptive designs” that have attracted so much attention in this decade go beyond this level of adaptation (and will be discussed later), but no specific details are included in the definition.

The second element of the definition, that of preserving the validity and integrity of the study, refers to the statistical and operational considerations utilized to provide the same level of statistical inference and integrity of process as classical “fixed” designs.  However, as we will see, the regulatory agencies have specific concerns which will progressively define the acceptable bounds of adaptive designs and the extent of their utilization in pivotal studies.  The debate between the regulatory agencies and the industry is ongoing and the regulatory approach will evolve as our experience deepens.

A missing element of the definition is the word “planned”.  Expected adaptations in study design must be declared prospectively allowing all “stakeholders” to plan accordingly and for the regulatory agencies to provide input regarding the validity of the approach.  Planning and meticulous execution of the plan is of outmost importance in maintaining the integrity of a study based on an adaptive design.

D.    Types of adaptive designs:

There are adaptations that address most aspects of a clinical study.  Thus, the classification of adaptive designs presents a number of challenges.  A “rules” based classification is certainly possible, although somewhat cumbersome.  In general, adaptive designs modify four basic elements of the study (occasionally referred to as rules): (a) the manner in which the patients are randomized into the study (allocation rule); (b) The number of subjects that will be included (sampling rule); the rules by which a decision will be made to move to a different stage or modify elements of the study such as the primary endpoint and/or the method of analysis (selection rule); and how the study will be brought to an end (stopping rule).  Thus, utilizing a matrix of rules, designs can be classified by the number and type of rules they modify.    Such a classification may be detailed but it fails to provide relevant information to persons outside the biostatistical community.

Another classification scheme is based on the phase of development for which the adaptive design is best suited. Certain adaptations are utilized mostly in early development studies, others in the confirmatory and pivotal phase.  Such a classification scheme is simple, but lacks specificity.

In this paper, I have classified the studies on the basis of how the results of the interim/continual analysis affect the post-interim structure of the study.  This is essentially an “operational” classification and one that I think provides a real-world insight to these designs.   My classification is not drastically different from the one presented by Coffee and Kairalla,[6] albeit simplified.  The reasons for the simplification are explained below, along with the outline of this classification.

·      Model-based/continuous assessment adaptive designs: A group of designs commences mostly with modeling and simulation, initiates subject treatment, continuously assesses collected data and then assigns consecutive patients to dose groups on the basis of the fit of the collected data to the model.  These designs are utilized mostly in early clinical development for dose finding and ranging. 

·      Group sequential/sample-size re-estimation (SSR) designs: This second group consists of group sequential designs[*] in which the interim analysis is utilized to recalculate the sample size and possibly the number of additional interim analyses.  They were introduced by Bauer and Köhne[7] based on the premise of planning a multi-stage study as a meta-analysis of independent studies.  In these designs, there are usually no changes in the groups being tested and in patient characteristics after the interim analysis.  Heterogeneity between stages is less pronounced than in response adaptive designs.

·      Group sequential/response adaptive (RA) designs: This third group consists of designs in which several elements of the study, such as enrollment criteria, number of arms/doses, randomization scheme, primary endpoint, stopping rules and switching between non-inferiority to superiority or vice versa,  are modified in the 2nd stage after subject response in the 1st stage is assessed. The heterogeneity of the study is thus more pronounced in stage II of the clinical trial than in the SSR designs. These designs are very operationally demanding and can be used both in early and late phases of development.

·      Adaptive randomization designs: In this final group belong studies that utilize an adaptive randomization scheme to balance the groups of the study for a variety of prognostic factors that may have a bearing on outcome.    

One can expand the categories of adaptive designs by including hybrids and combinations of these designs.  In certain classifications, seamless phase II/III clinical trial designs[6] are treated as a separate category of “adaptive designs” although they are simply administrative constructs of the designs described above.  Seamless Phase II/III studies may utilize a model-based/continual assessment adaptive design in phase 2 for dose finding, followed by a phase 3  study with the doses of interest utilizing  either a sample size re-estimation, an adaptive response or a classical fixed group design.  Such seamless designs certainly save time and money as they decrease the logistical requirements and compress the time for starting the Phase 3 study.  They do have a number of operational disadvantages including certain regulatory reticence when used in pivotal phases (Section F.)    Also, sample-size re-estimation designs can include elements of response adaptation. Readers are advised to examine other classifications of these designs.  Both Chow and Chang3 and Dragalin,[8] among others, have surveyed and classified these designs in detail:.

1.     Model-dependent/Continual Reassessment Adaptive Designs

These designs are normally used in early development, in phase 1 and phase 2 studies.  In the early stages of development, the effort consists of carefully defining the risk/benefit ratio throughout the dose spectrum. Thus, early studies attempt to define the maximum tolerable dose (MTD) and the minimum effective dose (MED). In this process, there is a moral imperative to quickly discontinue ineffective or toxic doses of a drug while obtaining reliable information.   Adaptive designs can successfully address both of these requirements.

In Phase 1 safety studies, adverse reactions and toxicities are the primary endpoints.  Phase 2 dose-ranging studies usually utilize surrogate efficacy endpoints or a combination of pharmacodynamic/biomarker endpoints.  Although usually their correlation to the clinically beneficial endpoint is somewhat weak,[†] they can produce a statistically meaningful differential response to treatment with relatively few subjects.  In the classical Phase 1 methodology, a typical dose escalation (usually 3 + 3) approach[‡] is employed until the MTD is defined. The adaptive approach is based on the creation a priori of a model of the toxicity curve expected; this model is continuously adjusted and refined with the results obtained from each individual patient.  The dose selected for each subsequent patient depends on the presence or not of a dose-limiting toxicity (DLT) in the previous patient.   If a DLT occurs, the dose is lowered; if not, it is increased.  This design is based on a continual reassessment method (CRM) of subject information introduced by Quigley et al.[9]  A number of variants merging this method with a traditional 3 + 3 design soon appeared.[10],[11]  Some of these hybrid methods do not require a prospectively defined dose toxicity curve but proceed in the manner of the classical 3 + 3 design.

Dose ranging studies in Phase 2 present similar challenges and opportunities.   In the classical approach, which is still prevalent in use, the study subjects are randomized equally to a spectrum of doses] deduced from previous preclinical or clinical studies.   The sample size is declared prospectively, calculated in the typical process that utilizes the expected differential in response between doses, the desired level of significance and power.  Despite its simplicity, such a design may be inefficient: it may miss a substantial section of the dose-response curve.  Even if it does not, the vagaries of sample size calculation may mean that the variance in response may be such that no statistical significance can be obtained.

Adaptive designs for dose ranging studies try to avoid these pitfalls and provide a more reliable definition of dose response although there are number of limitations and caveats in their use.[12]  These designs are typically based on the continual reassessment method (CRM) outlined above for phase 1 clinical studies.  These CRM-based designs can be combined with a fixed randomization design for a confirmatory study in a seamless Phase II/Phase III construct.

2.     Group Sequential/Sample-size Re-Estimation Designs

Group sequential designs were developed early on to allow a clinical study to be stopped after an interim analysis if the results showed that there has been a convincing demonstration of efficacy or a demonstrable futility of achieving a meaningful efficacy result.[13] 

Group sequential designs possess a certain appeal because many of the elements that lead to the estimation of the sample size for the study are informed assumptions that may not be representative of the response in the population and/or the selected sample.  It is well known that enrollment criteria substantially modify the sample from the overall disease population so that many assumptions based on previous results or clinical observations may no longer apply.  More often than not, they are be derived from groups or subgroups of patients with different demographics and prognostic factors from those of the prospective population of the planned study. 

The major elements that go into the calculation of a sample size (beyond the desired level of significance and power) are the expected clinically beneficial effect[**] (δ) and the anticipated variance (standard deviation, σ).   In certain cases, regulatory guidances may provide detailed information as to the size of the effect necessary to gain marketing authorization.   . 

In classical group sequential designs, a study is powered by the best guess for the lowest clinically beneficial effect required to obtain marketing authorization. This results in the maximum sample size to be assessed in the study. The reverse is true for adaptive group sequential/sample size re-estimation designs.  In these, a more optimistic value for the clinically beneficial effect is selected, thus allowing the study to start with a relatively small number of patients and increase the sample size, if needed, based on the response assessed at the interim analysis.[14] 

Of course, what applies to the treatment effect applies equally as well to the variance.  I in this case, one may examine the variance of the primary endpoint by pooling all results and thus avoid unblinding during the interim analysis.[15]  In this case, the type I error rate is fully preserved and no statistical penalty needs to be paid. 

Does the sample size re-estimation methodology present specific advantages?  In cases in which the guess for the clinically beneficial effect is based on less than ideal information, and in which one wants to avoid expanding unduly the scope of early development to define it better, such designs may have a definitive utility.  In a variety of therapeutic areas such as neurology, oncology and others, earlier phases of development utilize surrogate endpoints (e.g., brain lesions in the case of multiple sclerosis, progression-free survival in oncology).  The typical endpoint for the pivotal phase must correspond to clinical benefit (e.g., time to progression to next stage in multiple sclerosis); thus prior information based on surrogate endpoints or prior clinical trials may only provide informed guesses as to the possible treatment effect and the statistical underpinnings of the study.[††]   

There are a number of concerns: the differences observed at the interim, based on small samples may be due to chance fluctuations and may mislead sample re-estimation.  In addition, if the sample size in the 2nd stage is very large in comparison to the sample size of the Stage I, a remote possibility exists that a treatment may be declared beneficial if the results of stage I are highly positive but the much larger dataset of stage II is negative.[16]   Also, adaptation has a price: adaptive group sequential designs are not as statistically efficient under certain circumstances as the classical “fixed” approaches and may result in more patients treated prior to the conclusion of the study than it would have been the case otherwise.[17],[18]  There are regulatory concerns: regulatory authorities would need to be convinced that these designs are not utilized for the sake of minimizing the Phase 2 program.    In addition, designs in which not only the sample size but also the number of interim analyses are subject to change may face regulatory obstacles, as more than one interim analysis may make it difficult to convince regulators that the integrity of the study has been adequately maintained (Section F).

3.     Group Sequential/Response Adaptive Designs

These are designs in which substantial changes are introduced at the interim stage based on patients’ response to treatment with the sole purpose of “amplifying” this response, concentrate resources and patients into effective treatments and generally improve the possibilities of a successful outcome.  The changes may include reduction in dose groups, modification of enrollment criteria, and switching from superiority to non-inferiority.  Also, randomization may become unbalanced in stage II, allowing allocation of more patients to groups with superior outcome or by the discontinuation of treatment arms with inferior outcomes (play-the-winner[19] / drop-the-loser designs[20]).  In certain cases, the adaptation following the interim analysis may include a change in the primary endpoint (or components of a composite endpoint) if the clinical benefit in a certain disease is not well understood and no specific regulatory guidance applies.  Thus, there is usually a substantial qualitative change between Stage I (study design prior to the interim analysis) and Stage II of the clinical trial.   These studies are operationally quite demanding for both the sponsor and for the investigative sites in which the study is carried out.

Many two-stage designs are appropriately powered in stage II.  Because the 1st stage may be lacking adequate power, the decision as to which group to drop/modify may be often based on precision analysis.  In the final analysis of the data, methods exist that allow the combination of  p-values of endpoints from various stages of the study.[7],[21]    

The regulatory approaches for such designs are discussed in more detail in the discussion of the EMEA’s reflection paper in Section F.

4.     Randomization Adaptive Designs

Certain study designs may also modify the randomization algorithm on the basis of covariates (covariate adaptive randomization designs) if certain patient characteristics appear to be important in the response, thus balancing out prognostic factors.[22] These approaches maybe valuable in studies with relatively small number of patients in which the study groups may not obtain the appropriate balance in factors deemed capable of modifying response to treatment.

E.     Utilization of Bayesian Statistics

Certain of the approaches discussed above are based on the “frequentist” approach to statistics, in which hypothesis testing is based on data collected directly from the sample tested in the clinical study.  Continual reassessment method(CRM)-based designs (discussed in model-dependent adaptive designs) and certain multistage designs depend of Bayesian statistics. Bayesian statistics  allow the probability distribution of a given endpoint from previous information (earlier stages of the study, previous studies or other observations) to be combined with the probability distribution derived from  the currently tested sample.  Although it may be tempting or even intuitive to utilize previous information, there are substantial issues that may advise against such an approach, (such as sample differences and methodology changes) that may introduce a bias in the interpretation of results.  Thus, a lot of objections to the use of Bayesian statistics revolve around combining prior information with current observations to provide an “optimal” estimate.  The obvious question here is that if that prior information is solid, why perform another experiment and if it is not, why undertake the exercise? In addition to this intrinsic problem, the computational and programming aspect of Bayesian statistical analyses presents major problems.  They have been based on individual approaches that present difficulties to third parties and regulatory agencies in the evaluation of their statistical properties. Overall, there are no generally accessible programmed solutions that meet regulatory requirements, which explains the regulatory reticence in the utilization of Bayesian inference in pivotal studies.   

Since CRM-based studies mainly driven by Bayesian inference address the sponsors “learning” requirements in early development, regulatory inhibitions about their use in that context are few. The FDA is attempting to redress the difficulty of evaluating the statistical robustness of programming Bayesian statistics. However, the agency’s timelines are not clear.  In the progress report on the Critical Path Initiative (See Section F) for 2008, [23] the FDA reports that it is working with a “large statistical software company” under a cooperative research and development agreement to produce a commercially available software package that would allow the design and analysis of Bayesian-driven clinical trials.  This package should have commenced beta testing at the end of 2009.[23] The EMEA is also examining the use of Bayesian methodology.  In the final report from the EMEA/CHMP think tank on innovative drug development, there is a commitment to investigate such methods and possibly render them usable and evaluable by the agency.[24]

F.     Regulatory Agencies and their Response to Clinical Study Innovations

1.     The FDA’s Critical Path Initiative and Design Issues in Clinical Studies

The FDA initiative is called the Critical Path Initiative and it was launched in March of 2004.  At its launch, the FDA issued a report,[25] stating that the launch of this initiative was an imperative because of the slowing pace of development of new agents.  It highlighted the low productivity, rising costs of development, increased risk and a higher failure rate.  It also stated that predicting success was very difficult with current tools, an issue discussed extensively in a previous article.  The FDA estimated that a compound entering clinical research has only an 8% chance of reaching the market, substantially lower than the 14% chance that has been historically established before the first decade of the 21st century.[25] In the launching of the initiative, the FDA promised to bring its expertise and accumulated data to bear in the development of a new toolkit for drug development.

The Critical Path Initiative essentially aims to create a number of technologies that would facilitate drug development.  These “integrated technologies” consist mainly of developing better animal models of disease; extending information on useful biomarkers that can provide dependable information on disease progress and potential clinical benefit and may make earlier phases of development more predictive of the final outcome; pharmacogenomic information that can predict response to the drug; new clinical trial designs and statistical capabilities; and improved quality assessment tools.  A report by the FDA at the end of 2008 highlighted its progress in a variety of these areas. [23]

a.      The FDA’s View of Adaptive Designs

A more detailed critique of adaptive clinical trials design was published in 2006, authored by members of the FDA’s Division of Biometrics and Office of Biostatistics.[26] In that paper, the authors stated several of the areas of uncertainty introduced by adaptive designs and in some cases questioned the need for them.  A very strong argument was made that if the criteria for the planned adaptation are carefully defined a priori, a more statistically efficient “fixed” design may be available.[17] and that the estimate of the treatment effect at the interim may be inadequate in providing guidance for sample size re-estimation.[27] The authors also noted that in study designs in which an arm of the study is dropped, reallocation of the alpha to the remaining arms may lead to a substantial inflation of the type I error.  They caution that, in such a case, either the reallocation of the unused alpha should not be attempted or the planned sample size of the terminated arm should be distributed to the remaining treatment arms.[28] The authors also addressed the possibility of changing from superiority to non-inferiority.  They concluded that no adjustment to the alpha is necessary if superiority and non-inferiority are tested with the same confidence interval for the treatment effect.  However, they strongly advise setting and justifying the non-inferiority margin prospectively, and warn that a non-inferiority margin derived from interim data is not going to be interpretable.  In terms of changing the primary endpoint at the interim, the FDA authors conclude that this approach, however valid the statistical test employed, probably has no advantages compared to a “fixed” design with multiple primary endpoints in which the alpha is allocated by a Bonferroni adjustment.[‡‡] 

It was also emphasized that adaptive designs leave unclear which point estimate for the treatment effect can be reported in the product label.  This appears to be a serious issue for the authors.  In addition, the authors wonder what happens to the validity of multiplicity adjustments for secondary endpoints after a number of adaptations.  They also present a number of case studies to highlight issues with adaptive designs and conclude with a number of logistical concerns.

Gallo and Mauer[29] have provided a response to this paper on behalf of the industry.  They defend the overall concept of the adaptive designs because they claim that studies should not necessarily be held hostage to initial assumptions that may be proven wrong during the conduct of the study or to unfavorable chance events at an interim of an non-adaptive group sequential design.  The authors also defend the estimates for the treatment effect obtained by adaptive designs, claiming that many methodologies of fixed designs, such as carrying forward the last observation or worst-case imputation, also modify such estimates included in product labels.    

b.     The FDA Guidance on Adaptive Designs

From the onset of the Critical Path Initiative, the FDA has indicated that it is working on a number of guidances and has highlighted some issues and opportunities in presentations by its senior personnel.  However, as of the writing of this paper, these guidances have not as yet appeared.  Members of the FDA team have presented outlines of a draft guidance in recent meetings.[30]  The outline does not exhibit any substantive departures from the opinions voiced by Hung et al.[26] It reiterates that the field is in evolution and that a final guidance should be understandable by a wide audience.  The presentation of the early draft focused on concerns regarding the integrity of the study following the interim analysis and the difficulty of interpreting results from studies utilizing adaptive designs.  In many ways, the guidance outline indicates that the FDA’s approach closely resembles that of the EMEA’s as revealed by the latter’s reflection paper published in 2007.  Also, very much like the EMEA, the FDA is concerned that that adaptive designs may be used to shortchange early development, thus expanding the use of an experimental agent well before there is adequate safety information to allow such a step. 

2.     The EMEA initiative

The EMEA was also alarmed with the slowing pace of innovation in drug development.  Its approach is similar in broad outlines although there are differences in detail, foundational philosophy and implementation.[§§]  The EMEA’s response to adaptive clinical trial designs and other issues of pharmaceutical development is an element of the Innovative Medicines Initiative (IMI) and its Strategic Research Agenda (SRA).[***]  In the process of forming a response, the EMEA assembled a think-tank group that consulted both academia and corporations on ways for speeding development; this group also examined the methods by which the agency may reorganize and modernize itself in order to streamline drug development. The findings of the EMEA/CPMP drug group were published in 2007.   Some of the findings echoed positions enunciated earlier by the FDA on the development of biomarkers and flexible study designs.

a.      The EMEA’s Reflection Paper on Adaptive Designs in Confirmatory Studies

In October 2007, the EMEA also released a reflection paper on adaptive (flexible) designs in confirmatory clinical trials.  Since this is the first document officially released by a major regulatory agency on this issue (although it is not a guidance), it is worthy of a more detailed examination.  It should be pointed out that the “Reflection Paper” is very similar in concept and occasionally utilizes the same language as the paper by Armin Koch of German drug regulatory authority which was published in 2006.[31]

The reflection paper[32] mostly centers on considerations for studies with planned interim analyses and outlines practices that may be acceptable for a positive review of an application.  It does not discuss statistical approaches in detail apart from general statements regarding the control of type I error, makes no mention on the acceptability of Bayesian statistical methods in these studies and reiterates a number of pre-existing guidances which it regards as still applicable to clinical trials with flexible designs.

The guidance places a lot of emphasis on the confidentiality of the results of interim analyses, a common thread in the concerns of regulatory agencies.  The EMEA apparently feels that the danger of compromising the study is substantial and insists that the need and the number of interim analyses should be carefully justified.  The agency would need to be convinced, for example, that interim analysis for sample size recalculation is not undertaken because of the insufficiency of earlier studies.  Thus, the EMEA states that flexible designs should not be utilized as a method of substantially reducing the “learning” phase of clinical development.  The inherent dangers of the approach can only be overcome by careful reasoning that the agency can accept.  Thus, extensive consultation on this point would be crucial.  The agency has further concerns about the possible bias being introduced by interim analyses.  The reflection paper makes clear that an analysis of the data prior to and following the interim analysis would be necessary to show that the homogeneity of the study has been maintained.  Obviously, this may be possible with adaptive group sequential designs but not with multi-stage adaptive randomization designs which, by definition, introduce heterogeneity.  Because of the possible introduction of bias by the interim analysis, the reflection paper is rather negative on the introduction of more than one interim analysis.  The agency assumes that the need for more than one interim analysis indicates that conditions of the study fluctuate far more than it is acceptable for a confirmatory trial.

The EMEA discusses the possible consequences of stopping a given study “early”.  Many in the development community would take exception to the term “early”[33] but the agency is apparently concerned that an “early” discontinuation may compromise the safety data expected to be collected.  Since the EMEA feels quite strongly on this issue, the best approach would be to contemplate the first interim analysis only when at least the minimum number of patients for safety determination has been accessed as per ICH guidelines.  In conclusion, the agency specifies that “interim analyses without realistic objectives should be avoided” but it fails to define what these realistic objectives may be.  My guess is that these “realistic objectives” of the interim analyses would need to be decided on an individual basis in consultation with the agency and early stopping of clinical studies should be undertaken with great caution.  If an “early” stop to the study has occurred, the agency is very clear that it wants to see two analyses: the analysis of the data collected at the interim analysis stage and an additional one in which the patients that were accessed and treated after the commencement of the interim analysis are included.  Any discontinuities between these analyses may present problems at the review stage.  It would all depend on the magnitude of difference between the interim and final analyses although no specific guidance is offered.  The EMEA is apparently convinced that interim analyses, on average, over-estimate the true treatment difference and this should be kept in mind when providing a rationale for them to the agency. 

The EMEA has a variety of reservation regarding adaptations.  They stem from the belief that the need for such adaptations spring from incomplete prior development and errors on assumptions.  Thus, the reflection paper states that re-assessment of sample size may also indicate that many of the assumptions about the design were simply “erroneous”.  In the case of non-inferiority clinical studies, the non-inferiority margin must be re-evaluated and re-justified if the sample size has been re-estimated.

In planning the sample size, the treatment effect should be well defined prospectively and the agency would apparently frown upon justifying a treatment effect as clinically beneficial on the basis of interim results.  This is in line with the EMEA’s strong concerns about changing the main endpoint of the study at the interim result stage.  In the reflection paper, the agency authors makes clear that the main endpoint in pivotal studies is selected on the basis of its clinical benefit and not on the basis of displaying differences between groups. Although it does not provide details, the EMEA states that rejection of null hypothesis based on results from different endpoints in multistage designs is unacceptable.

The agency appears to harbor strong reservations for designs that discontinue study arms, especially the placebo one.  The reflection paper notes that study populations may vary at different stages, depending on the inclusion or exclusion of a placebo arm in these stages.  It is clear, however, that discontinuing certain ineffective doses of the test drug may face less opposition than discontinuing controls or the placebo.   The agency clearly indicates that it much prefers studies with unbalanced randomization to studies that discontinue treatment arms if the approach is statistically robust.    Thus, in a multistage trial design contemplated to support registration in the EU, it may be necessary to continue enrolling patients in the 2nd stage in the placebo and control arms in an unbalanced randomization scheme..

As a note of caution for arm discontinuation in multistage designs, the reflection paper also clearly indicates that in studies with more than one dose it would not be sufficient to show that some dose of the drug (combining all drug doses) is effective.  The selected dose should achieve this aim on its own.  In addition, in a multi-stage setting, only data from the treatment that has gone through all stages would be acceptable as part of the label claim, even if arms discontinued in earlier stages showed superiority against placebo. 

The EMEA repeated its typical guidance in switching between superiority and non-inferiority.  However, it is rather hostile to a study design that proves non-inferiority at the interim and continues treatment to show superiority.  The agency prefers two independent non-inferiority studies the results of which may be combined in a metanalysis to prove superiority.   

The reflection paper is negative on Phase II/Phase III combinations, if these studies are the sole element in support of a marketing authorization.  The draft guidance flatly states that such studies are not going to be acceptable for filing purposes and should be used to investigate correlations between surrogate endpoints and to define the optimal dose regimen. 

G.    Operational Considerations

In classical study designs, data are examined after the study has been completed, all data have been gathered and the blind removed.  By their very definition, this is not the case with adaptive designs.  As the study is planned to be modified on the basis of accumulated data, a number of operational considerations must be taken into account in order (a) to collect the data within an appropriate time frame and (b) to maintain the integrity of the study while examining that data, especially if this requires unblinding.   Both of these efforts place a substantial burden on the conduct of the clinical study and the obligations of the sponsor, the sponsor’s agents and investigative sites.

In all studies in which interim analyses are scheduled, speed and accuracy of data collection is imperative; otherwise the delay in this step can be substantial.  The pressure for timely and accurate data collection and auditing is even more pronounced in methods that require continual reassessment in model-dependent adaptive designs.  In addition, extreme care should be taken to assure that the both the sponsor and the investigative sites remain blinded as to the group assignments and do not bias the study in its later stages.  This may involve the removal of the sponsor from the committees that evaluate the data and render decisions to proceed or not with the study.  These committees may include a steering committee and/or a data safety monitoring board (DSMB) with well specified responsibilities and appropriate charters.  If the sponsor assigns employees to support these committees such as a biostatistician, programmer and/or data manager, and if the data accessed reside in the sponsor’s databases, then the appropriate “firewalls” should be put in place and they should be copiously documented.  It is obvious that for adaptive designs to be efficient, the main endpoint and other essential data should not require an excessively long period of time to be collected, otherwise treatment in stage 2 would be substantially delayed.  

In response adaptive clinical study designs, additional considerations may apply.  If the design addresses the possibility that  the drug is successful only in subset of the population tested,  these subpopulations should be carefully constructed and “nested.” The appropriate sample size for each subpopulation tested at the interim analysis stage should be defined.    

The operational demands of adaptive designs act as a barrier for their adoption by the organizations that may actually need them the most: the small biotech companies.  In adaptive group sequential/sample-size re-estimation designs in which subject numbers may be increased substantially from the starting estimate, securing funding for the largest feasible sample size may be just too difficult.  In multistage designs, the “winner” may be a smaller section of the population than originally envisaged, thus undermining pre-existing funding structures.    But beyond these general considerations, the everyday operational requirements of studies with adaptive designs are too demanding for the organizations of medium to small biotech companies.  The much greater emphasis in timely and accurate data collection and dissemination of information to all stakeholders, supervision of enrollment, constant examinations of the validity of the database, the maintenance and documentation of firewalls may be insurmountable obstacles for companies that are “virtual” in many of their functions and for which continuous monitoring of processes and regular training is beyond their means and beyond the expertise of their personnel.  The CRO and sponsor “organizational distance” imposes limitations on information flow and agile study and data management.  In addition, devolving important decisions regarding the study to independent committees may be beyond their capacity of senior management of small biotech companies to accept.  One may take the cynical view that with all the inefficiencies built into the whole R&D effort of small companies as the attain “focus”, adaptive designs are probably the least of their problems.

In larger pharmaceutical companies in which all the organizational pre-requisites exist and risk is well-apportioned to a large number of compounds, adaptive clinical studies may provide substantive money and time savings.  Progressively, as these designs mature and experience in dealing with them increases, their adoption by smaller companies may be easier.

H.   Recommendations

1.     The Planning Stage

So, how does one proceed with a study based on an adaptive design?  The answer to this question certainly varies with the capabilities of each organization.  First and foremost, all elements of the study must be carefully understood accounted for in the planning stage.  Any deficiencies in the plan can spell disaster later on. 

A full examination and possible revision of SOPs should be undertaken to make certain that no gaps exist and that there will be no deficiencies in compliance when dealing with management of data (blinded or unblinded) of an ongoing study.  As one may want SOPs to remain somewhat general, it may be appropriate to construct a number of best practices to address information access and flow, responsibilities, firewalls and other operational requirements.   In this context, both the monitoring and the data management plan should go into details and include a full risk mitigation plan that takes into account all eventualities.  It is also imperative that the clinical study team should undertake the effort of “educating” major stakeholders of the corporation to the issues that may be encountered. 

What should also be addressed in the planning phase and should be fully in place prior to the beginning of the study is the composition, charter, membership and of a DSMB or a steering committee for the study, if the study requires decision making by an independent entity. If needed and not previously employed, SOPs for the DSMB should also be compiled and all its members should receive adequate instruction in them.  The information flow between the corporation and the independent committee should be well regulated on the basis of both the DSMB and the sponsor SOPs.  It should be fully documented to assure regulators that study integrity was not undermined.

The study feedback loops should also be planned at this stage.  During the conduct of the study, these feedback loops should be continuously assessed to make certain that errors are kept to minimum, information flows as planned and no bottlenecks exist. It is very important that the study manager should be in control of the feedback loops and that the management structure is as centralized as possible.  A diffuse decision making in such a program can spell disaster.  Since the Stage I of all adaptive studies is crucial in further decision making, getting it right from the very beginning is imperative.

Maintenance of the blind is imperative.  In certain cases, designing the  of the blind may be challenging because of differences in test/control drug volume sizes, expected topical adverse effects, anticipated typical post-administration AEs, etc. Efforts beyond the usual should be undertaken to mask these differences during the conduct of the study.  If the maintenance of the blind is expected to be challenging, then the plans to proceed with an adaptive design should be reappraised.

2.     The Conduct Stage

Since a number of decisions taken after the interim analysis would be crucial to the success of the study, the quality of the data at the interim must be high.  The number of protocol deviations and violations should be kept to a minimum.  Although this is a good advice in general for all clinical studies, it has a special urgency in adaptive designs.  Usually, the rate of violations/deviations improves as the study goes on. Continuous corrective actions by study personnel improve the education and subsequent compliance of the investigative sites and ineffectual or non-compliant investigators are removed.  Unfortunately, in designs heavily dependent on an interim analysis, the margins are far tighter.  Corrective actions should be as timely as possible and information about them should be quickly disseminated to all sites.  The study management team should be “at the top of its game.”  All efforts should be expended to make certain that only the proper patients enter into the study, all tests and assessments are performed and completed within the appropriate time windows and that the protocol-mandated treatment algorithm is adhered to.  Too many missing data and too many deviations at the interim may seriously bias the adaptation decisions.  

In order to achieve high quality of data, a stable, well-trained and well-motivated study management and monitoring team is required;  Teams with decentralized management and high turnover rate may be inappropriate for such an effort.  Of course, investigative site education should be a thorough, ongoing and unremitting process.

3.     The Imperative of Full Documentation

It is imperative that all communications with the sites be documented and reviewed in as detailed a fashion as possible to make certain that any introduction of bias by the sponsor or any independent participant does not occur.  Detailed standard procedures and thorough documentation of interactions with sites may avert any suspicion by regulatory bodies of inadvertent introduction of bias if some “peculiarities” are detected in the data. 

The following example highlights such a case: Koch[31] examined a study in which three different stages were discernible (the first one was up to the interim analysis).  The experimental treatment achieved virtually identical results in all three stages, while the efficacy of the standard treatment declined considerably from stage to stage (the decline was statistically significant).  Koch stated that such discontinuities would raise concerns among regulators, unless “full reassurances exist that the treatments are fully (my emphasis) blinded to patients as well as observers.” Gallo and Mauer,[29] in their reply to Koch stated that within-study “drifts” may “occur naturally” possibly because of the experience gained by investigators during the trial or because of “natural shifts” in patient population.  I find this reply totally unconvincing, because if the changes in efficacy were caused by the investigators gaining experience, they would have affected the experimental rather than the standard treatment.  The reverse actually happened.  In addition, I am not sure what is “natural” in data drifts and patient populations and I think that the regulatory authorities would have the same uncertainty.

I.       Conclusions

The allure of adaptive designs in clinical studies is based on the promise of lowering costs, speeding up development and reducing attrition rates.  However, many of these promises depend on a flawless implementation of very complex procedures and methods of analysis that may not be well understood.  There is skepticism and caution within large regulatory agencies regarding their large scale adoption. The field is in evolution and the regulatory agencies are slowly responding to the challenges that such designs pose.  Their proponents, such as various CROs and biostatisticians, may be overselling their benefits, at least at present.

The complexity of implementation as well as regulatory caution essentially assures that progress in the field will be slow despite the excitement that has been generated in the last few years.  Also, the challenges of implementation (and possibly of conception) make it obvious that these designs will be utilized mostly within the confines of large, well-funded and well-staffed pharmaceutical companies. Unfortunately, these have not been the well-springs of productivity in research as of late.

At this time, it appears that the regulatory agencies will have little problem with adaptive studies in Phase 1 or 2.  In any case, as long as the ethics guidances are met, it is really the responsibility of sponsors to “learn” at this stage of development.  In fact, efforts for dose finding at these stages may provide a good test for a variety of adaptive designs and the opportunity to discover if these methods do provide more accurate information for a “go/no go” decision.

As usual, the regulatory agencies review early stage information at the end-of-phase 2 meeting (or equivalent) and its adequacy (or lack of it) shapes the regulatory feedback on the pivotal phase designs. Both the EMEA and the FDA have sounded strong warnings to sponsors about proceeding with adaptive designs in the pivotal phase without an adequate safety database after the Phase 2 program. Regulatory bodies may have a much easier time accepting adaptive designs in confirmatory studies  if surrogate or pharmacodynamic/ biomarker endpoints have been used in Phase 2.  In such circumstances, there would always be a good case that the assumptions regarding the clinical beneficial endpoint may not be precise and an adaptive design (such as sample size recalculation) would be the best way of addressing this uncertainty.

For those planning the clinical development of drugs and biologics, it is important to consider that, because of regulatory caution, substantive departures from the paradigm of “two well-designed confirmatory studies” with fixed designs should be adopted (a) only when the rationale is sound and has been fully accepted by regulatory authorities and (b) when there is the organizational capability to support such an effort. The same note on caution applies to contemplating and planning confirmatory studies with adaptive designs without compiling an adequate safety experience in the early phases. For well-funded corporations with adequate personnel and organization, adaptive clinical trials in early phases may save money and move the decision process faster and better than classical designs.

J.       Keywords

Pharmaceutical Development - Clinical Trial – Failure Rate – Clinical Trial Design –Adaptive Design – Group Sequential Design – Phase II - Phase III - Bayesian Statistics –Classification – Recommendations – FDA – EMEA – Critical Path Initiative – Innovative Medicines Initiative - Reflection Paper – Regulatory Guidance - Good Clinical Practices – GCP – Protocol Violations

K.    References

[*] In sequential designs, data are assessed after each patient is treated to compare the test statistic with the boundaries of the stopping rule; in group sequential designs, groups of patients are treated prior to an interim analysis to assess if the boundary has been crossed or not.  

[†] For the discussion of phase 2 study endpoints see: “Why do so many phase 3 studies fail? Part 1: The Effect of Deficient Phase 2 Trials in Therapeutic Areas with High Failure Rates in Phase 3 Studies”

[‡] The 3 + 3 design is based on enrolling 3 subjects per dose in an escalating manner.  If none of the patients has a dose limiting toxicity (DLT) at a given dose, 3 more subjects are treated in the next dose level.  If 1 subject displays a DLT, 3 more subjects are enrolled. If 2 subjects overall develop a DLT, then escalation stops and the previous dose level is declared as the Maximum Tolerable Dose (MTD)

[§] In these designs, 3 to 5 doses, placebo and/or active control is a typical configuration of the arms of the study

[**] The primary endpoint of a pivotal study has to correspond to a well-defined clinical benefit.  The terms “clinically beneficial effect” and “treatment effect” is synonymous here with the primary endpoint of a pivotal study

[††] Oncology presents certain challenges for group sequential approaches (either adaptive or not) because oncology studies utilizing such designs are likely to use progression-free survival (PFS) to assess efficacy during the interim stages, not overall survival (OS).  Thus, a stopping rule would have to utilize the surrogate endpoint.  The problem with this approach is discussed in summary by Hung et al.26

[‡‡] In a Bonferroni adjustment, the alpha is divided by the number of primary endpoints and then each endpoint is tested against the adjusted alpha.  However, other adjustment methods exist for dealing with multiple primary endpoints such as the Hochberg approach.

[§§] The FDA has formulated the CPI initiative and drives its implementation.  The EMEA pursues its agenda in partnership and collaboration with industrial groups

[***] IMI resulted from a partnership of the European Commission’s with the European Federation of Pharmaceutical Industries and Associations (EFPIA).

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