May you present new evidence to defend your patent after its application?

A competitor disputes the validity of your patent and argues that your original patent application did not contain sufficient evidence. Can you still use data you collected only later to defend the invention? Yes, under strict conditions. A ruling by the president of the Dutch-speaking Enterprise Court in Brussels on 15 May 2025, in a case between pharmaceutical giants Bristol-Myers Squibb (BMS) and Sandoz demonstrates how Belgian judges apply the EPO guidelines on this, confirming that the original application must make the later evidence "plausible.

The facts: a blockbuster drug and a generic challenger

The case revolved around apixaban, the active ingredient in pharmaceutical company BMS' successful anticoagulant Eliquis®. The protection of the basic patent (EP 415) had already expired, but was extended in Belgium by an Supplementary Protection Certificate (SPC) until mid-2026.

Generic manufacturer Sandoz however, already obtained licenses to market a generic version, "Apixaban Sandoz," and was considering a market launch before the expiration of the SPC. BMS then initiated prohibitory injunction proceedings to prevent this threatened patent infringement.

Sandoz defended itself with a counterattack: a claim for invalidation of the basic patent and thus also of the SPC. According to Sandoz, the patent was invalid because the original application (from 2002) did not show that apixaban worked better than already known substances. BMS had submitted crucial test results proving apixaban's superior efficacy only years later, during the renewal process. So the key question was: may the court take this "later submitted evidence" (post-filed data) into account?

The decision: the G2/21 guideline as a guide to plausibility

The Brussels injunction judge upheld the validity of BMS's patent and prohibited Sandoz from commercializing its generic product. The court based its ruling largely on the principles contained in the directional decision G2/21 of the Grand Board of Appeal of the European Patent Office (EPO).

The president followed the reasoning in the G2/21 decision, which states that subsequently submitted evidence may be used to support a technical effect (such as improved operation) provided that the effect was plausible based on the application as originally filed. The invention need not be proven in every detail from the start, but the technical teaching in the application must make it plausible to a skilled person that the claimed effect will be achieved.

The president thoroughly analyzed the original patent application (WO 652) and found several indications whether “pointers" that made the superior efficacy of apixaban plausible:

• The application explicitly set the goal of finding improved Factor Xa inhibitors with better pharmacological properties.
• Apixaban was mentioned in a list of preferred compounds.
• A detailed manufacturing example for apixaban was included (Example 18).
• The description showed that apixaban was produced in the largest quantity and subjected to additional purification steps.

Taken together, these elements made it plausible to the skilled person that apixaban was the most promising candidate. Thus, the subsequently submitted evidence, which confirmed the significantly improved effect of apixaban, did not serve to create an entirely new invention, but rather to confirm an effect already made plausible. Therefore, the president ruled that the patent satisfied the requirement of inventive step.

Legal analysis and interpretation

This ruling is an important affirmation of the G2/21 standard in Belgian jurisprudence. It creates a balance. On the one hand, patent holders cannot merely speculate and try to rescue an invention with new data afterwards. On the other hand, it recognizes that pharmaceutical research is a lengthy process and not all comparative data are already available at the filing date. As long as the original application lays a solid technical foundation and makes the intended benefit plausible, later evidence can be used in support.

One striking and problematic aspect of the ruling, however, is the scope of the injunction imposed. In addition to prohibiting commercialization, the judge ordered Sandoz to refrain from "distributing or otherwise disseminating, through any medium, information carriers such as leaflets, brochures, and so forth" that contain information about the product.

This communication ban is exceptionally broad and legally shaky. patent law gives the holder the right to prohibit commercial acts (such as selling or offering), not the right to censor the dissemination of information. The entire patent system is just based on the disclosure of technical knowledge in exchange for a temporary monopoly. Such an unmotivated and broad ban on speech runs counter to this principle and clashes with fundamental freedoms such as the freedom of speech and freedom of enterprise.

What this specifically means

• For the innovative company (patent holder): Your original patent application is the foundation. Make sure it not only describes the invention, but also contains sufficient evidence and technical context to make its benefits and effects plausible, even if you do not yet have all the final, comparative test results. This ruling shows that a well-prepared application can be successfully defended later. In an injunction claim, however, be cautious about asking for a total ban on communications; this may be considered an overreaching and unlawful measure.
• For the generic manufacturer (challenger): Attacking a patent merely because the final proof dates are missing from the original application is a weak strategy. You must show that the claimed effect was not plausible to a skilled person at the time. If you do get convicted, critically analyze the injunction imposed. An injunction that goes beyond the cessation of commercial acts and amounts to censorship may be successfully challengeable on appeal.

FAQ (frequently asked questions)

What is the G2/21 decision and why is it important for Belgian patent cases?
G2/21 is a decision of the board of appeal of the European Patent Office. It clarifies the conditions under which evidence obtained after the patent application (post-filed data) may be used to prove inventive step. Although Belgian judges are not strictly bound, they consider such decisions to be very guiding in applying patent law uniformly in Europe.

What exactly does "plausibility" mean in patent law?
Plausibility means that a skilled person must, based on the information in the original patent application and his general professional knowledge, find it plausible or credible that the invention can actually produce the claimed technical effect or benefit. It is not absolute certainty, but more than mere speculation.

Can a judge prohibit me from communicating about my product even if I don't sell it?
In principle, no. Patent law visions commercial exploitation. A blanket ban on communications, as was imposed in this case, is highly exceptional and legally questionable because it may clash with freedom of expression and the core principles of patent law itself.

Conclusion

The BMS/Sandoz ruling provides clear guidance for dealing with later-filed evidence in patent litigation, in line with the EPO's G2/21 standard. It underscores the crucial importance of a carefully drafted, content-rich patent application. At the same time, the ruling serves as a warning against the dangers of an overreaching injunction that threatens to violate fundamental rights.