Rifaximin – USA

Rifaximin – USA

On Aug. 10, 2022, Delaware court ruled polymorph and one MoU patents invalid whereas other MoU patent as valid.


Norwich (Defendant) submitted ANDA to the USFDA for approval to market a generic version of Xifaxan (Rifaximin), 550 mg tablets. Salix (Plaintiff) markets Xifaxan in the USA. Salix sued Norwich for infringement of twenty-six patents. Before trial, Salix narrowed its case to U.S. Patent Nos. 7,612,199, 7,902,206 (“the Polymorph Patents”), 8,642,573 , 9,421 ,195, 10,335,397 (“the HE Patents”), 8,309,569, and 10,765,667 (“the IBS-D Patents”).


Polymorph Patents:

Plaintiffs asserted two claims each from US’206 and US’199. Those claims relate to polymorph B with specific XRD peaks (5.4°; 9.0°; and 20.9°) with water content (about 4.5% to about 40%). Norwich admits and thus Court held that Norwich’ s ANDA product will infringe the asserted claims.

With respect to invalidation, Norwich argued that U.S. Patent No. 4,557,866 (the “Cannata” reference) inherently anticipates claim 4 of the ‘199 patent because it discloses a process that necessarily produces the claimed rifaximin B. But Court disagreed and said that this evidence does not amount to clear and convincing evidence that Claim 4 is inherently anticipated. Specifically, rifaximin forms such as alpha, delta are not necessarily derived from rifaximin B. Thus, to show that Cannata inherently anticipates Claim 4, Norwich would need to show that every time Cannata is performed, rifaximin B is produced. Norwich has not done so.

For Obviousness, Norwich contends that claims are obvious over Cannata in view of Normix Label / common knowledge. Norwich argued that the general knowledge would motivate a POSA to “identify the characteristics of the obtained rifaximin” using “routine methods.” Furthermore, Norwich argues that a POSA would recognize “that the crystallization solvent used by Cannata included water, which could lead to hydrate formation, and thus [the POSA] would have been motivated to analyze the effect of water on the crystalline form using conventional methods. Court agreed and said that the evidence is clear and convincing that a POSA would have been motivated to characterize the rifaximin produced by the Cannata processes. Cannata disclosed that rifaximin had strong antibacterial properties and low bioavailability, motivating a POSA to evaluate the substance as a potential drug candidate. Because the Cannata process for preparing rifaximin used water, a POSA would know about the potential for a hydrate to form, and be motivated to perform routine testing ( e.g. , KF or TOA) for water content and hydration formation. Thus, Norwich has proved by clear and convincing evidence that the claims are invalid as obvious.

For Written Description, Norwich argued that the polymorph patents improperly claim a genus, whereas the specification recites only a species. Salix responds that (1) the claims, on their face, are limited to the specific polymorphic form rifaximin B, rendering Norwich’ s genus characterization inaccurate, and (2) even if Norwich is right, the claims identify structural features common to the genus as required by the case law. Court agreed with Salix and said that the evidence shows that a subset of XRPD peaks can identify the polymorph. Moreover, patents claim only rifaximin B’ a polymorphic form which can be identified using the three peaks recited in the claims. Court thus rejecedt Norwich’ s written description challenge.


Method of Use patents:

Court concluded that Norwich’ s ANDA will induce infringement of the HE, and IBS-D patents. The HE claims are nonobvious and Norwich has failed to show a lack of adequate written description. The asserted IBS-D claims are invalid as obvious.


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