While clinical trials are indispensable for the development of new therapeutics, they can also jeopardise the patentability of later filed patent applications. EPO jurisprudence applies a nuanced analysis to determine whether information related to clinical trial drugs forms part of the state of the art. Central considerations include the public accessibility of the investigational drug and the existence – or absence – of confidentiality obligations. This article summarises key legal principles and provides insight into landmark decisions shaping the current practice.
When drafting patent applications for new therapeutic compounds or uses, pharmaceutical innovators face a strategic dilemma. Filing early is critical to securing priority under the first-to-file system and to avoid losing rights to prior disclosures. Yet, filing too soon – before robust experimental data is available – may compromise patentability. Without concrete evidence of the claimed therapeutic effect, patent applications may fall short of the EPO’s sufficiency threshold. This tension between timing and technical substantiation lies at the heart of patent filing strategies in the life sciences.
Clinical trials are the preferred means of acquiring sound data in support of a corresponding patent application. Yet, under European patent law, they may also serve as a double-edged sword: if details about a trial drug or its therapeutic effect are made public before the corresponding application is filed, this may amount to public prior use under European patent law.
This article reviews the EPO’s case law on public prior use in the context of clinical trials, addressing when such use may render an invention part of the state of the art within the meaning of article 54(2) European Patent Convention (EPC).
The legal framework: public prior use under the EPC
Article 54(2) EPC defines the state of the art as ‘everything made available to the public by means of a written or oral description, by use, or in any other way’ before the filing date. This broad definition encompasses not only written publications but also oral disclosures and public prior use.
To qualify as prior art, a public prior use must be established through clear and convincing evidence showing (1) what was used, (2) when it was used, and (3) how it was made available to the public.
These principles place a high evidentiary burden on parties seeking to invalidate a patent: the entire chain of events must be proven ‘up to the hilt’ (Case Law of the Boards of Appeal, IV.C.2.1). On the other hand, it is not necessary to demonstrate that the information was actually accessed – only that it was accessible to at least one member of the public. Clinical trial sponsors must therefore carefully manage the information flow during a study.
Public accessibility of the medication itself
One route by which a trial drug may become publicly available is through physical access by members of the public.
Case law from the EPO and national courts (see, eg, German Patent Court, 3 Ni 38/85 Adalat) recognises that clinical trials establish a special relationship of trust between the sponsor and the persons involved, including study personnel and trial participants. As long as this relationship remains intact, trial participants are not considered members of the public, and they are assumed to comply with the handling and use restrictions imposed by the sponsor.
A special relationship is more difficult to prove outside of the context of clinical trials – for example, in commercial settings (T 505/15) or physician-led medical treatments (T 945/09).
A particularly sensitive issue arises in trials where participants are allowed to take investigational drugs home. In such cases, the EPO evaluates whether the sponsor maintained control over the drug despite its removal from the clinical environment.
In the well-known case of the contraceptive Yasmin® (T 7/07), participants were informed of the active ingredient (a micronised form of drospirenone) and given take-home tablets. Due to the lack of stringent drug accountability procedures and the absence of a requirement to return unused study drug, the sponsor was deemed to have lost control over the study drug. This allowed the theoretical possibility of third-party analysis, rendering the composition publicly available and destroying novelty of the formulation patent.
A similar issue arose in T 2250/13, where the examining division concluded that third-party analysis was possible despite requests for participants to return unused medication. Although the appeal was later withdrawn, the case illustrates the fine balance between trial logistics and public accessibility.
In contrast, the board in T 670/20 found no public accessibility in a take-home drug thrombosis trial where strict drug accountability was enforced under the EMEA Guidelines for Good Clinical Practice. Patients were required to use the medication as directed and return unused study drug. The board found that this arrangement barred the participants from freely disposing over the investigational drug, thereby precluding public access. Importantly, the sponsor’s control over the trial drug was not found to be breached by the absence of a legal sanction tied to non-compliance with the imposed handling requirements.
These decisions underscore the need to implement strict drug accountability procedures, especially in studies involving take-home medication. This includes requiring participants to return unused medication, providing clear instructions on handling and use and ensuring that investigational drugs are not freely accessible to third parties. Such measures help maintaining control over the trial drug as recognised by the EPO Boards of Appeal, thereby reducing the risk that the clinical trial composition will be considered publicly available and novelty-destroying.
In general, information about the study drug and details of the clinical trial should be shared only on a need-to-know basis and confidentiality provisions included wherever possible.
Public accessibility of information about the trial drug
When clinical trials are not conducted with take-home medication, but in a hospital setting, the drug usually remains within the control of the study sponsor and cannot be freely accessed by the trial participants (see, by way of comparison, T 2395/22, where the trial drug was reconstituted before being brought to the patients for injection, and any unused quantities were disposed of in accordance with special regulations). This does not, however, entirely prevent novelty-destroying public availability: The information about the trial drug can become publicly available too.
In general, the EPO considers a piece of information as being available to the public within the meaning of article 54(2) EPC if a single member of the public who is not under an obligation to maintain secrecy has the possibility to access the particular piece of information (see, eg, T 239/16).
Therefore, even when trial medication is not dispensed for home use, public disclosure risks remain – particularly concerning information shared about the investigational product and the clinical trial setup.
Confidentiality and the nature of the information recipient
The decisive question is whether those with access to the information were bound – implicitly or explicitly – by confidentiality obligations.
EPO Boards have consistently held that:
- Medical professionals and investigators participating in clinical trials are generally presumed to be under an explicit or implicit obligation of confidentiality (eg, T 152/03, T 906/01). This protective veil of secrecy extends to those members of the clinical staff that are not directly participating in the clinical trial, and to personnel involved in preparing and shipping the investigated drug to the clinical trial institution (T 2395/22).
- Trial participants are not typically subject to express confidentiality obligations but implied confidentiality will usually be assumed due to the special relationship between study participants and clinical investigators. While participants themselves are not treated as ‘the public’ (T 598/12), the information they receive may become public if they are encouraged to share it (T 239/16).
- The doctor–patient relationship is typically deemed confidential. Discussions between trial patients and their own physicians are therefore presumed to be private.
Thus, the extent to which trial participants are informed and permitted to share details of the clinical trial plays a pivotal role in determining whether novelty is compromised.
Information flow to the trial participants
The mere fact that patients are encouraged to discuss their trial participation with their doctors, relatives or friends does not, in itself, breach the ‘special relationship’ between sponsor and participant (eg, T 670/20). This is because the precise technical features of the trial drug are not typically a piece of information on which patients base their decision to participate.
Moreover, it is not sufficient to argue that the trial participants are theoretically able to inquire about the trial drug. For example, in T 494/96, surgically implanted lenses supplied to physicians under investigation agreements were not deemed publicly available, despite the patients’ theoretical right to inquire about the composition. The board drew an analogy to a library entitled to order a book it never actually ordered.
Opponents frequently rely on informed consent forms as a starting point for their public availability argument. While those documents are not usually considered publicly available, it is common practice that patients who have signed the form receive a copy to take home with them, where its contents can potentially be discussed with third parties, including members of the public. This can lead to public availability of the consent form’s content (eg, T 239/16). It is therefore paramount that the patent owner controls the information presented to the patients via the consent form.
In the case underlying T 2395/22, the claim was directed to a lyophilised composition in a product-by-process context. The informed consent form only specified the active compound ‘PS-341’ and contained no further details on the composition or its production method. The board therefore concluded that no relevant information had become publicly available.
These examples highlight the importance of working with code names, timing disclosure of the chemical structure of active pharmaceutical ingredients (APIs) and tightly controlling the information flow to the trial participants. Sponsors must ensure that the participants receive all necessary information to make an informed decision about participating in the trial, while refraining from sharing technical details that could compromise patentability.
Implications for medical use claims
While novelty of a compound or composition claim is usually denied once the compound or composition has become publicly available, a different standard applies to medical use claims.
To invalidate a medical use claim, public disclosure of the therapeutic effect – not just the product – is required (eg, T 158/96, T 233/96, T 715/03, T 1859/08). The mere announcement of a clinical trial, without efficacy data, does not suffice. Spurred by clinicaltrials.gov disclosures being used as prior art, the past decade has seen a whole body of EPO case law develop around the legal test of reasonable expectation of success, which remains a case-by-case assessment.
Conclusion and outlook
The EPO’s approach to public prior use in clinical trials boils down to a case-specific analysis of confidentiality, access and control. While trial participants are usually not considered members of the public, a lack of effective confidentiality and drug accountability measures can lead to unintended public disclosures.
Clinical trial sponsors and patent applicants should therefore:
- whenever feasible, seek to file a European patent application before commencing clinical trials. In practice, data from preclinical studies or in vitro experiments are often adequate to meet the EPO’s sufficiency threshold for inventive step during examination and opposition;
- ensure that confidentiality agreements are in place;
- define expectations for trial participants‘ handling of investigational products, and maintain robust drug accountability procedures, particularly in outpatient settings;
- recognise that even disclosures lacking efficacy data can impact inventive step assessments.
For parties seeking to challenge the validity of a patent based on public prior use, the case law discussed above underscores the importance of substantiating all relevant facts with detailed and verifiable evidence. In the context of clinical trials, this means carefully examining not only whether the investigational drug was physically accessible to the public, but also whether trial participants were in a position to use or disseminate it freely. Where drug accountability procedures, confidentiality agreements or other restrictions were in place, a public prior use attack is likely to fail unless there is concrete proof that such safeguards were ineffective or not enforced in practice.
The legal framework in this area continues to evolve and clinical trial disclosures remain a challenging field also from a patent policy perspective. Arguably, it should generally be possible for an inventor to test their invention before filing a patent application. In fact, in many cases, the inventor will only be able to complete the invention by testing a hypothesis and it will generally be in the public interest that patent applications are not filed merely on the basis of speculation, but on the basis of sound research results. This is no different in the field of pharmaceuticals than in other areas of technology. One of the key differences compared to other areas of technology is, however, that pharmaceutical inventions generally require extensive clinical trials with humans that, for ethical reasons, require comprehensive information and the written, documented, voluntary consent of the participating patients. For ethical reasons, the patent applicant often does not have control over what information is included in the patient consent forms and to what extent the patient is under a secrecy obligation. If these ethical requirements lead to a situation where every patient information in the context of testing a drug that has not yet been approved is regarded as prior art, that would make patent protection based on data from clinical trials impossible. Arguably, this was not intended by the EPC and does not correspond to the purpose of patent protection, which is to provide an incentive for innovative research. It thus remains to be seen where the future case law develops in this area.
Patent practitioners and clinical trialists must remain vigilant, especially when devising filing strategies and preparing patent applications based on clinical trial results. A seemingly minor lapse in managing trial confidentiality may have far-reaching consequences for patent validity.
Dieser Artikel wurde erstmal im Juni 2025 auf IAM veröffentlicht; weitere ausführliche Analysen finden Sie unter IAM The Guide to Life Sciences: Key issues for senior life sciences executive 2025.
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