The German Federal Court of Justice (BGH) recently issued a landmark decision (X ZB 3/25) on February 25, 2026, clarifying the requirements for the disclosure of inventions involving purpose-bound product protection.

The Case at Hand: The dispute centred on a patent for an agent to treat fructose intolerance containing the enzyme glucose isomerase. While the application described the enzyme’s ability to convert fructose into glucose in a laboratory setting (in-vitro), it failed to provide sufficient evidence or plausible indicators for its effectiveness within the human body (in-vivo). Consequently, the patent was revoked.

Key Takeaways from the BGH:

• Reasonable Expectation of Success: For a patent claiming purpose-bound product protection, the application must contain information that establishes at least a “reasonable expectation” that the substance possesses the claimed therapeutic property.
• Beyond Pure Theory: If the assumption of efficacy is based solely on theoretical conclusions without factual indicators for practical application, the disclosure is deemed insufficient.

• Threshold of Information: While clinical trials are not strictly mandatory at the filing stage, the skilled person must be able to assess the probability of success with “sufficient reliability” based on the application’s content.

💡 Practical Tips for Patent Practitioners:

1. Prioritize Data Generation: This ruling highlights the risks of filing “paper patents.” If in-vitro results are used, ensure they are comparable to physiological conditions. In this case, the BGH noted that industrial in-vitro conditions do not automatically prove efficacy in the complex environment of the human small intestine.
2. Establish Plausibility Early: A causal link between the active ingredient and the treatment must either be known from the state of the art or plausibly demonstrated in the application.
3. Burden of Proof Dynamics: While the opponent in opposition or nullity proceedings generally bears the burden of proof regarding non-enabling disclosure, they can successfully challenge a patent by demonstrating its “speculative nature” through technical arguments. The patentee must then be able to support the expectation of success.
4. Consistency in Legal Standards: The “reasonable expectation of success” is a crucial criterion for both enabling disclosure and inventive step. A weak disclosure may fail at the very first hurdle of patentability.

Conclusion: The BGH is raising the bar for the quality of patent applications in the life sciences sector. To secure protection for medical applications, applicants must provide more than just a sound theory—they must provide a credible path to practical success.