Lonsurf® (tipiracil)
Case Name: Taiho Pharma Co. v. MSN Labs Private Ltd., No. 19-2342-JLH (D. Del. Jan. 23, 2025) (Hall, J.)
Drug Product and Patent(s)-in-Suit: Lonsurf® (tipiracil); U.S. Patent No. 10,457,666 (“the ’666 patent”)
Nature of the Case and Issue(s) Presented: The ’666 patent claims stable crystal forms of tipiracil hydrochloride. The ’666 patent also noted three crystal forms of tipiracil hydrochloride: Crystal Form I, Crystal Form II, and Crystal Form III. Taiho asserted claim 3 of the ’666 patent, which recited Crystal Form I having a purity of at least 90% by mass. During discovery, the parties stipulated that claim construction was unnecessary. As the case progressed, it became clear that the parties disputed the meaning of the term “purity.” The term “purity” was dispositive of infringement. The court found that MSN did not infringe.
Why MSN Prevailed: Taiho argued that “purity” referred to chemical purity. In other words, Taiho believed that the 90% figure referenced the percentage of the mass that is tipiracil hydrochloride, as opposed to chemical impurities in the API. Conversely, MSN argued that “purity” referred to “polymorphic purity.” According to MSN, the 90% figure refers to the percentage of the mass that is in Crystal Form I. The court began by explaining that neither claim 3, nor any of the other claims, were helpful in resolving the parties’ dispute.
As to the specification, the court concluded that it strongly supported MSN’s construction. As a starting point, the court explained that the specification acknowledged that methods for producing tipiracil hydrochloride were known in the art, but that they resulted in mixtures of different crystal forms. Then under the heading, “Solution to Problem,” the specification stated that “through trial and error, the inventors discovered a method for advantageously obtaining a highly-pure form of Crystal I.” The specification went on to explain that “high purity” is polymorphic purity: “[h]igh purity used in the present invention means that at least 90% by mass, preferably 95% by mass, and more preferably 99% by mass of the crystals of [tipiracil hydrochloride] are the crystals of the present invention.” The court concluded that the only mention in the specification of a 90% figure, as recited in the claims, referred to polymorphic purity.
The court next addressed the prosecution history. While the examiner initially understood “purity” to refer to chemical purity, the parties later treated “purity” synonymously with polymorphic purity. Indeed, later in prosecution, the examiner expressed that a claim requiring “having a purity of at least 90% by mass” meant “having a crystal Form I purity of at least 90%.”
