Enanta Pharmaceuticals, Inc. v. Pfizer Inc. (22-cv-10967).

In 2022, Enanta accused Pfizer of infringing its U.S. 11,358,953 Patent, which claimed compounds that inhibit an enzyme critical in the replication of the COVID-19 virus.  Enanta claimed that one of the components of Pfizer’s Plaxovid drug infringed the patent.  Enanta prepared infringement contentions that asserted that a particular portion of the Plaxovid compound met the limitation of an “optionally substituted C₁-C₁₈ alkyl” group.  Pfizer asserted that this contention failed to explain how the portion of Plaxovid qualified as such an alkyl group, and moved for an order requiring updated contentions.  Pfizer also propounded an interrogatory seeking the complete legal and factual basis for this contention.  Meanwhile, Pfizer served noninfringement contentions which Enanta asserted were ambiguous as to this particular limitation (of possible import, the specification of the patent does not identify the Pfizer component as one of the substitutions contemplated by the claim term).

Judge Boal noted that the Local Rules of the District of Massachusetts requires an infringement plaintiff to serve infringement claim charts “identifying, with as much specificity as reasonably possible” where and how each element is found in each accused product.  This requires more than a simple repetition of the claim language – an analysis must be presented.  It does not, however, require the disclosure of specific evidence of require actual proof.  Under this standard, she determined that Enanta’s contentions were sufficient, as they showed which component of the Pfzer drug were asserted to meet the specific limitation.  She found that Pfizer’s argument regarding how the portion of the Pfizer drug could satisfy the claim element was an argument on the merits of the contention, which is ”beyond the scope of preliminary infringement claim charts.”  She accordingly denied Pfizer’s motion with respect to the contentions.  She did, however, find that Pfizer’s interrogatory sought information beyond that required in infringement contentions under the local rules, and that Enanta had failed to provide a suitable response thereto.  She thus ordered Enanta to supplement its response.

Judge Boal ruled similarly with respect to Pfizer’s noninfringement contentions, finding that they sufficiently identified which claim elements were not met by the accused drug.  She further denied without prejudice Enanta’s motion to compel a more detailed response to Enanta’s interrogatory seeking the factual and legal basis for the denial that the substituted alkyl limitation was met.  She noted that it is Enanta’s burden to prove infringement, and that it must present its infringement theory to Pfizer (in the form of an updated interrogatory response) before Pfizer should be required to present detail on its noninfringement position.  Otherwise, Pfizer would be required to “negate every conceivable infringement theory.”