Kim & Chang successfully obtained a ruling from the Intellectual Property High Court (the “IP High Court”), stating that the scope of a patent on a novel active ingredient covers its solvate forms even during the patent term extension (“PTE”) period, despite the narrowed scope during PTE (IP High Court Decision 2023Heo13438, October 23, 2024).

Daiichi Sankyo is the patentee of a substance patent covering edoxaban, the active ingredient of the oral anticoagulant tablet Lixiana®. In this case, a Korean generic company filed a scope confirmation action at the Intellectual Property Trial and Appeal Board (the “IPTAB”) in 2022, challenging the scope of the patent during its PTE on the grounds that (i) edoxaban propylene glycol solvate, a modified solid form, did not fall within the scope of the patent during PTE, and that (ii) the solvate had been intentionally excluded from the patent scope under prosecution history estoppel.

The IPTAB initially ruled in favor of the generic, stating that the solvate was outside of the scope of the PTE and had been intentionally excluded from the patent scope under prosecution history estoppel. However, in the appeal to the IP High Court, our firm argued that under the principles established in the Supreme Court’s prior Vesicare decision (regarding the PTE scope of a substance patent) and Forxiga decision (regarding prosecution history estoppel), the PTE should still cover the generic’s solvate product. The Vesicare case involved a situation where a generic argued that its product used a different salt form from the original approved product, and therefore was outside the scope of the PTE for the substance patent, which is limited to covering the approved product. The Supreme Court in that case essentially held that as long as a person skilled in the art easily could have derived the salt form from the documentary evidence, the salt form was still within the scope of the PTE. Our firm argued that the same logic applied to this case and that the solvate should be considered within the PTE scope, citing extensive documentary and expert evidence.

The IP High Court overturned the IPTAB’s decision, agreeing with our firm’s argument that solvate forms of an active ingredient still are within the scope of a substance patent during PTE, even when “solvate” forms are not expressly claimed as possible solid forms of the active ingredient. The IP High Court recognized that while the term “solvate” had been excluded from the claims during prosecution, this deletion did not evidence to surrender any substantive subject matter, because the deletion was made to expedite allowance in response to descriptive support and clarity rejections, and a person skilled in the art readily would have been able to recognize and screen all possible solid forms of a novel substance even without specific examples in the specification.

This case is significant in further extending the logic of the Vesicare decision to make it more difficult for generics to easily circumvent substance patents by making simple changes to their generic products, such as changing the salt or solvate forms used, by rejecting an overly narrow view of the PTE scope, and emphasizing that the applicant’s subjective intent must be given significant weight in determining whether deleted terms amount to surrendered subject matter under prosecution history estoppel.