IP Law Daily, PATENT—D. Del.: Patent infringement case against Lupin over proposed generic product will not proceed, (Aug 28, 2026)

By Carolin Dennis, B.Sc., LL.B., LL.M.

The patent owner failed to establish that the proposed generic product infringed any of its asserted patent claims relating to formulations of ivacaftor.

In a case involving patents for a precise compound to treat cystic fibrosis, Vertex Pharmaceuticals Inc. (Vertex) failed to prove infringement relating to its formulations of ivacaftor, the federal district court in Delaware has held. The district court rejected all of Vertex's patent infringement claims because it was trying to claim that its patents cover a range of ivacaftor concentrations that it failed to patent (Vertex Pharmaceuticals Inc. v. Lupin Ltd., No. 22-cv-966-SB (D. Del. Aug. 24, 2026)).

Background. Vertex sold several drugs for the treatment of cystic fibrosis containing active ingredient ivacaftor. One of these drugs is Kalydeco. According to Vertex, an effective ivacaftor drug would comprise “about 10% by weight to about 80% by weight” ivacaftor. Using the 80% or about 80% specifications, Vertex got a range of patents for an ivacaftor drug. Lupin Limited and Lupin Pharmaceuticals (collectively, Lupin) submitted Abbreviated New Drug Application No. 217431 to the FDA, seeking approval to market a generic version of Vertex's Kalydeco oral granules prior to the expiration of patents that cover Kalydeco and its use. Vertex sued Lupin under the Hatch-Waxman Act, claiming that Lupin’s application infringed U.S. Patent Nos. 10,646,481 (the ‘481 patent); 11,564,916 (the ‘916 patent); 12,458,635 (the ‘635 patent) and 10,272,046 (the ‘406 patent). Two of them claim a drug containing exactly 80% ivacaftor and the other two claim “about 80%” ivacaftor. To show direct patent infringement, Vertex must prove either literal infringement or infringement under the doctrine of equivalents.

Literal infringement. Vertex conceded that Lupin did not literally infringe any of its claims that specify 80% ivacaftor exactly. Instead, it alleged literal infringement of its “about 80%” patents. Vertex’s argument for literal infringement relied on its expert, Dr. Berkland who read “80% ivacaftor” as a shorthand for a “high drug load” and the phrase “about 80% ivacaftor” to literally cover a wide range of percentages, “to at least 70 to 90% as a range.” The district court found Dr. Berkland’s “high drug load” approach unpersuasive because the phrase “high drug load” appears nowhere in the patents or their prosecution. Dr. Berkland failed to persuade the district court that drugs should be categorized as high or low load instead of by percentages. He also failed to give a concrete definition of “about 80%” and offered no scientific or principled basis to conclude that Lupin’s 74% ivacaftor drug is literally the same as about 80%.

By contrast, the district court found Lupin’s expert, Dr. Donovan, completely credible. Though she too did not give an exact percentage range, she limited it to less than a couple of percentage points. Her opinion was based in part on Vertex’s own patent prosecution, which specified the weight of ivacaftor down to a tenth of a percentage point. In the context of Vertex’s patents, the examiner thought that “about 80%” included 79.9%, and “about 0.5%” included 0.55%. Those statements comport with reading “about” even more narrowly than Dr. Donovan’s view and a far cry from Dr. Berkland’s “high drug load” approach. Therefore, the district court found Dr. Donovan testimony credible and adopted her reading of “about.” Additionally, the district court concluded that because Lupin’s compound varies from Vertex’s by more than a couple of percentage points, there is no literal infringement.

Infringement under the doctrine of equivalents. Vertex argued as a fallback that the drugs are functionally the same under the doctrine of equivalents. However, both the claim language and prosecution history point against the doctrine of equivalents here.

Starting with the claim language, the district court noted that Dr. Berkland’s testimony instead of opining on percentages or ratios, spoke of “high drug loads” and “very high drug loads” with no evidence that those are terms a drug maker would use. However, Vertex specified its claims down to half a percentage point. The “inherent narrowness” of those specifications belies Vertex’s efforts to assimilate 74.257% to about 80%. Next, considering the prosecution history the district court noted that the doctrine of equivalents could not impermissibly vitiate the limitations that Vertex argued for when prosecuting its patents. Here, to get its patent, Vertex emphasized how surprising the result at 80% was, and the examiner viewed about 80% as introducing variance of a tenth of one percent.

The district court noted that there are two ways to prove that the doctrine of equivalents applied: the function-way-result test and the insubstantial-differences test but neither worked Vertex’s way. The function-way-result test does not fit generic drugs because that test would ask whether a new drug does the same work in the same way as a patented one and virtually all generic drugs do. Vertex’s argument rests on the bioequivalence of Lupin’s drug: Both drugs use an amorphous dispersion of ivacaftor to treat cystic fibrosis. Nevertheless, bioequivalence is not enough to prove infringement. If it were, selling any generic of a patented drug would be illegal.

Thus, many courts find the substantial-differences test “more suitable” for generic drugs. Under that test, Lupin infringes if the differences between its drug and Vertex’s patent claims are “insubstantial.” Nevertheless, the intrinsic evidence does not suggest that a person of ordinary skill would view 74.257% and 80% ivacaftor as equivalent drug loads. Moreover, Vertex and Lupin make their drugs using different processes: wet versus dry granulation. However, the district court noted that Vertex insisted that the similar (though not identical) dissolution profiles mean that any difference is insubstantial which is just another way of saying the drugs are bioequivalent. However, Vertex cannot use bioequivalence to effectively outlaw generics.

Accordingly, the district court rejected all of Vertex's patent infringement claims.

The Case is No. 22-cv-966-SB.

Judge: Bibas, S.

Attorneys: Derek James Fahnestock (Arsht & Tunnell LLP) for Vertex Pharmaceuticals Inc. Cortlan S. Hitch (Morris James LLP) for Lupin Ltd.

Companies: Vertex Pharmaceuticals Inc.; Lupin Ltd.

Cases: Patent DelawareNews