A comparator is a substance used in a controlled clinical trial as a comparison to the investigational substance. The comparator can be an active medicinal product (active comparator), a placebo or – in certain study designs – the standard therapy. The choice of comparator has considerable implications for the study design, the regulatory validity of the results and the ethical justifiability of the trial. Regulators such as the EMA and FDA generally require, for pivotal trials, a comparison with the established standard of care, where one exists.
Types of comparators
Various types of comparators are used in clinical trials:
- Placebo: A preparation without active ingredient that matches the investigational substance in appearance, taste and consistency. Placebo-controlled trials allow demonstration of the absolute efficacy of a substance, but are only ethically justifiable if no effective standard therapy is available or if the trial concerns add-on efficacy.
- Active comparator: An authorised medicinal product used as the comparison arm. This approach allows demonstration of non-inferiority or superiority relative to the existing therapy and is ethically required where a standard therapy exists.
- Standard of care: The currently recommended treatment according to applicable guidelines – this can be a single medicinal product, a combination, or even a non-pharmacological procedure.
- Dose-response comparator: In some trials, different dosages of the investigational substance are compared against each other, without an external comparator.
Regulatory requirements for the comparator
The selection of the comparator must be scientifically and regulatorily justified in the study protocol. The ICH E10 guideline “Choice of Control Group and Related Issues in Clinical Trials” provides detailed recommendations on the choice of control group. The EMA generally expects a comparison with the active standard of care, where available. In placebo-controlled trials in indications with an available therapy, ethical justifiability must be explicitly established – for example through the short duration of the trial, an add-on design, or the absence of clinically relevant disadvantages for patients in the placebo arm. The alignment of the comparator with the standard of care actually used in the target population is also an important aspect of the external validity of the trial.
Procurement and quality assurance of the comparator
The procurement, storage and distribution of the comparator are subject to the same GMP requirements as the investigational substance itself. For active comparators that are commercially available, authenticity and quality must be demonstrated. In certain cases – for example in trials conducted in countries where the comparator is not authorised – over-encapsulation or blinding of the comparator is required to ensure the trial’s blinding. This requires corresponding pharmaceutical development and quality controls. Responsibility for providing a suitable comparator generally rests with the sponsor, who may delegate this task to a specialised CRO or contract manufacturer.
Relevance for clinical trials
The choice of the right comparator is a strategic decision with far-reaching consequences: it influences the regulatory acceptance of the study results, the ethical justifiability of the design, and the commercial positioning of the product after authorisation. A comparator that is too weak (e.g. placebo instead of the active standard) may lead to endpoints that are statistically easier to achieve, but will fail to convince regulatory authorities and the market. Conversely, a comparator that is too strong can make it more difficult to demonstrate superiority.
Particular care is required when the comparator is not uniformly available internationally or when different formulations exist in different markets. In such cases, early procurement planning is essential to avoid supply shortages during the trial. Shelf life, storage conditions and transport requirements must also be aligned with the sponsor and the responsible investigational site during the planning phase, since delays in the supply chain can have a direct impact on the study timeline. Full-service CROs such as mediconomics support sponsors in the scientific and regulatory justification of the comparator choice as well as in the practical procurement, over-encapsulation and GMP-compliant provision of the comparator.
Frequently asked questions (FAQ)
Is a placebo-controlled trial always permissible?
No. The use of placebo as a comparator is only ethically justifiable if no effective standard therapy exists, if it is an add-on design (all patients receive the standard therapy in addition to the investigational substance or placebo), or if the short duration of the trial ensures that patients do not suffer lasting harm. The Declaration of Helsinki and the ICH E10 guideline set clear ethical limits here, which are enforced by ethics committees and regulators.
What does a non-inferiority trial mean with regard to the comparator?
A non-inferiority trial compares the investigational substance with an active comparator and aims to demonstrate that the new substance is not substantially worse than the comparator – within a predefined tolerance limit (non-inferiority margin). The choice of this margin must be regulatorily justified and is based on historical data on the efficacy of the comparator versus placebo.
What logistical challenges exist in comparator procurement?
In multinational trials, procuring a uniform comparator can be complex: the product may not be authorised in all trial countries, regional formulation differences may require over-encapsulation, or import permits may need to be obtained. Early planning – ideally in parallel with study protocol development – is therefore essential to avoid delays in the study start-up.
Regulatory references
- ICH E10: Choice of Control Group and Related Issues in Clinical Trials
- EU Regulation 536/2014 (CTR): requirements for investigational medicinal products and auxiliary medicinal products
- EMA Guideline on the choice of the non-inferiority margin (2005)
- Declaration of Helsinki (2013), Section 33: use of placebo
- EU GMP Annex 13: Manufacture of Investigational Medicinal Products