German Federal Court of Justice (Bundesgerichtshof), order of 25 February 2026 – X ZB 3/25 – Fructose Intolerance Agent · ECLI:DE:BGH:2026:250226BXZB3.25.0
In a decision handed down on February 25, 2026, the X. Civil Senate (Patent Senate) of Germany’s Federal Court of Justice (Bundesgerichtshof, BGH) revisited a recurring question in pharmaceutical and life-sciences patent law: what does a patent claiming purpose-bound substance protection actually have to disclose about the substance’s therapeutic suitability? The Court’s answer is a useful reminder that, for medical-use claims built around a known compound, the asserted therapeutic effect is the heart of the invention—and it cannot rest on speculation.
Background: the patent and the dispute
The patent in suit was German patent DE 10 2007 008 664, filed on February 20, 2007, with grant published on July 29, 2021. It concerned an agent for use in fructose intolerance. Claim 1—on which six further claims depended—was directed to an agent for use in fructose intolerance containing glucose isomerase, acceptable carriers and/or excipients and added metal ions (selected from Mn²⁺, Mg²⁺, Zn²⁺, Fe²⁺, Co²⁺ or Cu²⁺ and mixtures thereof), with the composition containing no 5-D-fructose dehydrogenase.
The underlying idea was mechanistic: glucose isomerase can convert fructose into glucose, so the enzyme is meant to convert dietary fructose in the food pulp into glucose before it can cause the symptoms associated with fructose intolerance.
An opponent challenged the patent. The Federal Patent Court (Bundespatentgericht), 14th (Technical) Senate, decided the opposition under § 61(2) sentence 1 no. 1 of the German Patent Act (PatG) and revoked the patent by decision of November 22, 2024. The patentee appealed on points of law (Rechtsbeschwerde), which the Federal Patent Court had expressly admitted under § 100(1) PatG.
The outcome
The appeal was admissible but failed on the merits. The BGH dismissed the Rechtsbeschwerde at the patentee’s cost, leaving the revocation in place.
Key findings of the decision
1. A purpose-bound substance claim protects the substance’s suitability for the stated medical use
The claim was treated as purpose-bound substance protection within the meaning of § 3(4) PatG. The Senate reaffirmed its established line of authority that the subject matter of such a claim lies in the suitability of the substance for a specific medical purpose—ultimately an inherent property of the substance itself (referring to its Kollagenase I decision, X ZB 5/13, BGHZ 200, 229).
2. The claimed therapeutic suitability must actually exist—and be plausibly disclosed
Because suitability is the protected core, it must genuinely be present. The Court was careful not to impose a rigid evidentiary threshold: experimental data or clinical trials are not strictly mandatory. However, the Senate drew a clear line:
Where the asserted therapeutic effect of the substance is not made plausible by any experimental data in the originally filed application documents, the question of speculation can arise.
In other words, an applicant need not supply a full clinical dossier, but cannot fall back on a bare assertion of medical effect either.
3. On the facts, the disclosure amounted to speculation
Glucose isomerase was a long-known, commercially available enzyme whose ability to convert fructose into glucose was itself not new. The application described the mechanism and the intended dosing, but—on the Court’s assessment—did not provide a sufficiently plausible and comprehensible demonstration of the therapeutic suitability and tolerability of orally administered glucose isomerase for treating fructose intolerance. The teaching of the patent therefore came down to speculation rather than a credibly disclosed therapeutic effect.
4. Consequence: no purpose-bound protection—and a bridge to insufficiency of disclosure
The Senate confirmed that a patent claiming purpose-bound substance protection under § 3(3) or § 3(4) PatG may not be granted (or maintained) if the substance does not have the claimed suitability. Significantly, it noted that where a claimed property of the substance is objectively absent, this can also mean the invention is not sufficiently disclosed—linking the suitability requirement to the separate ground of insufficient disclosure (mangelnde Ausführbarkeit).
5. A safeguard for granted patents: revocation requires certainty
The decision also restated an important counterweight. Once a patent has been duly granted, the legal position the patentee acquired can be taken away only where it is established beyond doubt that it was wrongly obtained (citing X ZR 83/21). Here, that high bar was met.
Practical takeaways
- Plausibility at filing matters. For medical-use and purpose-bound substance claims around known compounds, the therapeutic effect should be made plausible in the application as filed—mechanistic reasoning alone may not suffice.
- The suitability is the invention. When the active substance is already known, the newly asserted medical suitability carries the patent and must be credibly disclosed.
- Two grounds, one weakness. A poorly substantiated therapeutic effect can undermine both the availability of purpose-bound protection and the sufficiency of disclosure.
- Revocation still needs certainty. The “beyond doubt” standard protects granted patents—but it is not insurmountable where the file lacks any supporting data.
Why it matters
The decision is a clean statement of how German patent law treats the dividing line between a disclosed therapeutic property and an unproven hope. For applicants in the pharmaceutical, nutrition and “food-for-medical-purposes” space—particularly those repurposing well-known enzymes or compounds—the message is to build the application around credible support for the claimed effect, rather than relying on the inherent properties of a known substance and a plausible-sounding mechanism.
The full text of the order is available from the Federal Court of Justice (PDF).
