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Suresh Keshav Bowalekar
Managing Director, PharmaNet Clinical Service Pvt. Ltd., Marwah Center, 7th Floor, Krishanlal Marwah Marg, Andheri (East) - 400 072, Mumbai
India

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In the initial period of 1900, or even a little before, the efficacy of any new treatment used to be assessed on the basis of information gathered through the medical report of one patient or several patients (case series). In very few studies, the efficacy of treatment used to be very obvious, even in a small sample of patients. In the rest (relatively large number) of the studies, it was not that easy to draw a meaningful conclusion with regard to the efficacy of treatment, as the number of patients exposed to the treatment was relatively less. Thereafter, began a period of studies designed to evaluate the efficacy of treatment using a large number of patients. Bradford Hill noticed that all these studies were uncontrolled, and came out with the idea of conducting randomized clinical trials (RCT) in the field of medicine. [1] Thus, for a long period of time, RCT continued to be the best method for comparing the effects of two treatments. [2],[3] The objective of the RCT was to show the superiority of one treatment over the other - in most cases, the other treatment used to be placebo.

Showing superiority of a new treatment or test treatment (TT) over placebo (P) or conducting 'placebo-controlled' trials has been the gold standard for many years in drug development. [4] However, with the increased availability of established treatments with proven efficacy, the placebo-controlled trials started facing ethical issues. This gave rise to an era of 'active-controlled' trials and the focus shifted from showing TT being superior to P to showing TT 'as good as' the standard treatment (ST). Statistically, it was not possible to show exact equality in the efficacy of the two treatments, hence, it was demonstrated that the effect of TT was 'as good as' ST. Subsequently, the phrase 'as good as' got replaced by the word 'equivalence' and the category of 'equivalence trial' came into existence.

Statistical tests used in superiority are called superiority trial tests. If the superiority trial test is significant, one concludes that the efficacy of TT is different from that of ST. Furthermore, if the result is in favor of TT, the conclusion is that TT is statistically and significantly superior to ST. However, a nonsignificant superiority test is misinterpreted as an indirect evidence of 'no difference' between the two treatments or 'equivalence of the two treatments'. Unfortunately as per the statistical principles of hypothesis testing, if the statistical test implies that the difference is not the statistically significant, then it cannot be concluded that the two treatments are 'equivalent.' Hence, use of apt statistical principles is very important for setting up a null hypothesis for 'equivalence' trials or 'non-inferiority (NI)' trials.

It is well known that the trials using non-inferiority designs are being conducted since 1982, [5] and many products have been approved by regulatory agencies based on the results of studies conducted using non-inferiority design. [6] However, the 'Draft Guidance for Industry: Non-Inferiority Clinical Trials' was distributed for comment purposes only, in March 2010, by the US Food and Drug Administration (FDA). [7]

Regulations on adequate and well-controlled studies (21CFR 314.126) describe the following four types of concurrently controlled trials for providing evidence of effectiveness:

Placebo-controlledNo treatmentDose-responseActive treatment (active-controlled)

The first three types mentioned above are superiority trials, and attempt is to show that TT is superior to the control (placebo, no treatment or a lower dose of TT). The fourth active-controlled type can also be categorized as a superiority trial, if the objective of active-controlled trial is to show that TT is more effective than the active-control / standard treatment (ST). Generally, the difference between two active treatments (TT and ST) is less than that between active treatments ST and P or TT and P, hence, achieving statistical significance with the same number of study subjects may fail to show superiority. Hence, the intention of such a trial is not to show superiority, but to show that TT is not worse than the comparator, which typically is the standard treatment (ST) or an active-control.

Three important reasons for conducting active control trials are:

Assay sensitivity: Assay sensitivity is a property of a clinical trial defined as the ability to distinguish an effective treatment from a less effective or ineffective treatment. [8] It should be appropriately used in the context of NI trialsEthics: It is unethical to use placebo as a control when established treatments with proven efficacy are available in the marketComparative evaluation: This is required to examine how TT compares with ST (which can be an active treatment) available in the market. ST must be known to be effective in the population under study.

The purpose of active control can be to show that a TT is either

Superior to the active control orEquivalent to the active control orNon-inferior to the active control

The objective of equivalence trials [9] is to determine whether or not the TT is therapeutically similar to the existing ST (active control), whereas, the objective of NI trials is to determine whether or not the TT is no worse than the existing ST. As mentioned earlier, it is impossible to prove the exact equality, hence, a margin (Δ or M) of non-inferiority for a primary endpoint is defined in advance. NI or the equivalence margin Δ(or M) is the degree of acceptable inferiority between the TT and the ST, where a trial needs to predefine at the design stage. The margin (Δ or M) chosen should be smaller than the 'effect size'. The effect size is defined as the expected difference between ST and P. It is a reliable and realistic estimate of the 'difference' between the effects of ST and P.

In the equivalence trials, two treatments are labeled as equivalent if the treatment difference falls between two limits - Δ (or - M) and + Δ (or + M). It is a two-sided approach, with symmetry around a value zero, for difference. For NI trials, the question under consideration is not symmetry. [9] The NI trials are expected to show that a TT (new) is worse by an amount less than the predetermined margin of Δ (or M). Many times this finding is accompanied by a list of other advantages like greater availability, reduced cost, less invasive, less harmful, ease of administration, and so on.

As of today, many non-inferiority trials have already been conducted and are being conducted, yet there are many areas that need the attention of the stakeholders of clinical trials as well as regulatory bodies. The basic idea is to sit together and bring about clarity in terms of various requirements, in order to draw a meaningful conclusion, scientifically acceptable to all. Some of the requirements needing immediate attention are listed herewith:

 Design: Three Arm Trials or Two Arm Trials

References