Orange Book Blog

One of the most commonly recurring and fascinating issues in Hatch-Waxman cases is the presence of “about” in claims. Such claims are a challenge for generic defendants, who lack certainty on how they can safely design around such claims, but also presents patentees with challenges as well as they must then demonstrate that “about” covers the claimed range and fend off indefiniteness challenges.

On its face, an “about” claim seems to run afoul of Section 112’s requirement for “claims particularly pointing out and distinctly claiming the subject matter” which the inventor regards as invention. Of course, there are cases finding such claims invalid for indefiniteness, including most recently for example in  Enviro Tech Chemical Services, Inc., v. Safe Foods Corp., No. 2024-2160 (Fed. Cir. May 4, 2026). But the Federal Circuit has also long held that words like “about” and “approximately” may be appropriately used to “avoid[] a strict numerical boundary to the specified parameter.” OrthoMcNeil Pharm., Inc. v. Caraco Pharm. Lab’ys, Ltd., 476 F.3d 1321, 1326 (Fed. Cir. 2007) (quoting Pall Corp. v. Micron Separations, Inc., 66 F.3d 1211, 1217 (Fed. Cir. 1995)). When a word of approximation like “about” is used, the range must be reasonably certain based on the “technological facts of the particular case.” Ortho-McNeil, 476 F.3d at 1326.

But patentees still must be able to point to such facts to prove infringement when the accused limitation is covered only by the broadening use of “about.” The challenges of doing so were well demonstrated recently in Vertex Pharms. Inc. v. Lupin Ltd., No. 22-cv-966-SB (D. Del. Aug. 24, 2026). In that case Judge Bibas (of the Third Circuit, sitting by designation) issued a short 10 page-written opinion finding Vertex’s claims to both “80%” and “about 80%” ivacaftor not infringed by Lupin’s drug, which consisted of 74.26% ivacaftor, either literally or under the doctrine of equivalents.

As a quick background, Vertex was hampered during prosecution by its own previous disclosure that an effective ivacaftor drug would comprise “about 10% by weight to about 80% by weight” ivacaftor. Vertex was able to obtain claims to “80% by weight” and “about 80% by weight” ivacaftor (along with specific excipients) based on arguing surprising results that occurred at 80% by weight. A sample claim is below:

1. A pharmaceutical composition comprising a single solid dispersion, wherein the solid dispersion comprises:
i. about 80 wt % of amorphous or substantially amorphous [ivacaftor] by weight of the solid dispersion[];
ii. about 19.5 wt % of [HPMCAS] by weight of the solid dispersion; and
iii. about 0.5 wt % of [SLS] by weight of the solid dispersion.

However, the examiner rejected an attempt to claim “about 72 wt% to about 88 wt%” ivacaftor in a related patent, concluding that such a range was obvious and that there was no proof the unexpected solubility result would hold across such a range.

During claim construction (which was handled by Judge Andrews), the court found no construction necessary, rejecting Lupin’s argument that “about” should be limited to rounding, i.e. “79.5-80.4” ivacaftor, 19.45-19.54% HPMCAS and 0.45-0.54% SLS, or else the claims would be indefinite. Somewhat strangely, Judge Andrews stated “Defendants provide largely conclusory statements regarding indefiniteness” despite himself noting that “[n]either party here could point to a place in the specification that clearly defined ‘about.’” Nor did Judge Andrews provide any guidance on how a POSA should assess “about,” leaving it entirely to the experts at trial.

Judge Bibas took over the case and conducted trial. Vertex conceded no literal infringement of the claims to exactly 80/19/0.5%, but the decision on literal infringement for the “about” claims turned entirely on how to apply “about” only for the 80% ivacaftor limitation. “Unfortunately for Vertex,” Judge Bibas found its expert “unauthoritative” because he was “less careful and less scrupulous and more willing to sign off on extreme statements.” Specifically, Judge Bibas was unimpressed with Vertex’s expert’s argument that “about 80% ivacaftor” meant “high drug load” and covered “at least 70 to about 90 percent as a range.” Judge Bibas noted the expert “gave no reason to think that is true” as “high drug load appears nowhere in the patents or their prosecution.”

In contrast, Judge Bibas found Lupin’s expert “completely credible” as “[s]he was meticulous” and “was admirably careful about what she could or couldn’t say.” Judge Bibas specifically found her opinion that “about” meant “nearly the same as” and limited to less than couple percentage points, noting that Vertex’s patent prosecution “specified the weight of ivactafor down to a tenth of a percentage point.”

Judge Bibas also found such testimony consistent with the examiner’s views, stated that “about 80%” included 79.9% and “about 0.5%” included 0.55% which “comport[ed] with reading ‘about’ even more narrowly than [Lupin’s] view-and a far cry from [Vertex]’s ‘high drug load’ approach.” Thus, Judge Bibas found no literal infringement.

Judge Bibas then considered the doctrine of equivalents for both the “80%” and “about 80%” claims together. To begin, Judge Bibas noted that the doctrine of eqvuialents is “an ‘exceptional’ path to proving patent infringement” and “applies only when ‘the nature of language makes it impossible to capture the essence’ and ‘every nuance’ of the patented invention.” Judge Bibas noted further, “many [claim] limitations warrant little, if any, range of equivalents” because of “the inherent narrowness of the claim language” and “prosecution history estoppel.”

Judge Bibas first held that Vertex’s arguments “would have erased the numerical limits in Vertex’s patents” and Vertex’s use of “claims down to half a percentage point” “belies Vertex’s efforts to assimilate 74.257% to about 80%.” As I’ll discuss below, Judge Bibas’ focus on “half a percentage” point strangely appears to relate to the HPMCAS and SLS limitations, not the ivacaftor limitation, despite Judge Bibas’ myopic focus on the ivacaftor limitation.

Judge Bibas also considered the prosecution history and that “Vertex emphasized how surprising the result at 80% was, and the examiner viewed about 80% as introducing variance of a tenth of one percent.” Though Judge Bibas appeared to view this as precluding the application of the doctrine based on prosecution history estoppel, he did not do any sort of estoppel analysis or identify any amendment or argument where the patentee surrendered scope. Interestingly, while noting the failure to obtain claims to “about 72 wt % to about 88 wt %” in a different patent in the background, Judge Bibas did not discuss this prosecution history when addressing DOE.

Judge Bibas continued that even if the doctrine of equivalents could be applied, Vertex could not prove infringement. He first held that the “function, way, result” test “does not fit generic drugs” as “virtually all generic drugs” work the same way as a patented one, citing Voda v. Cordis Corp., 536 F.3d 1311, 1326 (Fed. Cir. 2008) (which does not relate to generic drugs, so I am a bit unclear where he drew this rule from).

Judge Bibas then held the insubstantial differences test did not help Vertex, because “the intrinsic evidence does not suggest that a person of ordinary skill would view 74.257% and 80% ivacaftor as equivalent drug loads” in light of the “patent examiner read[ing] ‘about 80%’ to introduce a variance of roughly a tenth of a percentage point.” It was not entirely clear what Judge Bibas felt was “substantially different” about 74 versus 80%. Judge Bibas then noted that Lupin utilized a different process (wet versus dry granulation) and was unpersuaded by an argument that “the similar (though not identical) dissolution profiles mean that any difference is insubstantial” because “this is just another way of saying the drugs are bioequivalent.”

I found this case fascinating, and perhaps an example of a court reaching the right outcome for the wrong reasons.

First, I think the terms here should have been held indefinite. As I explained above, Judge Andrews’ claim construction order seemed to reflect that there was no guidance on how to be reasonably certain of the scope of the claims. Similarly, Judge Bibas did not credit either side as presenting “reasonably certain” scope of “about 80%” based on “the technical facts of the case.” And from my admittedly cursory review of the record, I’m not sure one could have found one. But it appears Lupin did not continue its indefiniteness arguments to trial. It is possible Lupin made a strategic decision that it would be better to prevail on non-infringement than invalidity, opening up the market for other generic competition.

Second, I find Judge Sibas’ emphasis on the examiner’s brief mention of a single example involving “about” to be a bit strange, as the judge repeatedly noted that the examiner “thought that ‘about 80%’ included 79.9% and ‘about 0.5%’ included 0.55%.” That the examiner gave such an example as falling within the scope of the claims does not to me clearly and objectively set an outer bound, especially such a limited range (which even Lupin did not advocate for). But Judge Sibas twice described the examiner as “read[ing] ‘about 80%’ to introduce a variance of roughly a tenth of a percentage point.” While not saying it outright, Judge Sibas seems to have adopted a claim construction of “about 80%” as 79.9-80.1%, even narrower than Lupin’s proposed construction, which Judge Andrews rejected, and then additionally applying that as a limitation on the equivalence range of 80%. But the entire purpose of “about” is to avoid strict numerical boundaries, and instead to focus on the “technological facts of the particular case,” which Judge Sibas does not seem to do. But again, the challenge is in trying to find reasonable certainty on a record that provides none.

Third, I find Judge Sibas’ analysis of the prosecution history to similarly be a bit strange. There was no dispute that the prior art taught using 10-80% ivacaftor, or that the claims to “80%” and “about 80%” were allowed after pointing to unexpected success in using an 80% formulation based on allegedly surprising solubility. What Judge Sibas’ discussion does not mention, however, is that the argument was that the prior art, while broadly disclosing 10-80% could be used, provided only an example with 50%. As Lupin argued, the “amount of API in the Lupin solid dispersion is much closer to the claimed 80% drug load than the 50% drug load in the prior art.” Judge Sibas did not seem to seriously grasp with this argument. The more problematic part of the prosecution history (strangely given little discussion) was Vertex’s inability to obtain claims to “about 72% to about 88%.”, discussed more below).

Ultimately, however, I do think Judge Sibas’ decision is correct. Whether applying the “about” broadener to the limitations or applying the doctrine of equivalents (which largely become the same analysis), it seems clear the claims could not cover Lupin’s product.

The claims require either exactly or about 80% ivacaftor, 19.5% HPMCAS and 0.5% SLS. The parties seemed to agree that Lupin’s generic product was approximately 74.26% ivacaftor, 22.28% HPMCAS, and 3.47% SLS. While I do tend to agree it is a bit difficult to read 74% as “about 80%,” I find some force to Vertex’s argument that a POSA would read “about” to include “the batch-to-batch variability inherent in pharmaceutical manufacturing” and encompass 10% variance (and 80% is not very precise, having only one significant figure), which might explain the ivacaftor limitation. More compelling to me is an argument Vertex made that Lupin’s ANDA would permit an 80% ivacaftor product because it is within 10% of the specified 74.26%, i.e., even under Lupin’s construction its ANDA still literally infringes (and infringes the exact 80% limitation).

However, Vertex still seems to have a problem in how it can succeed in proving that 3.46% SLS is “about 0.5%” or equivalent to 0.5% no matter how you slice it. I cannot find anywhere where Vertex ever explains how 0.5% SLS could possibly be “about 3.5%” which is well outside of the batch-to-batch variability one would expect. While Vertex attempted to argue the precise weight percentages (especially for SLS for example) were not important, such a broad reading of the claims clearly contrasts with the specificity of the actual limitations, especially the SLS limitation, and Vertex’s argument would clearly seem to vitiate at least the 0.5%/about 0.5% SLS limitation. Thus, I think Judge Bibas reached the correct result.

What would have been a more interesting question to me is whether a broader claim to 80% ivacaftor or about 80% ivacaftor without specific amounts of HPMCAS and SLS would have read on a 74.26% ivacaftor product (putting aside the argument that the ANDA permits 80% ivacaftor). While clear Judge Bibas believes the answer is no, that to me would have been a much closer call.

However, Vertex would have had a significant problem in that it attempted to claim ranges in a related patent of about 72-88%, and failed to convince an examiner to allow such claims. And though it didn’t make it much into the opinion, I think the ultimate problem Vertex had is that it was asking for “about 80%” to be viewed as broader than the rejected 72-88% and cover 70-90%, and did not have a compelling argument for why it should be granted claim scope the patent office rejected.

This is where the arguments get a little confusing, and I think the parties and court somewhat conflated determining the literal scope of the “about” limitation and the equivalence of the non-about claims. In some ways these are the same inquiry, and the patentee cannot apply equivalence to the about claims. See Cohesive Techs., Inc. v. Waters Corp., 543 F.3d 1351, 1372 (Fed. Cir. 2008) (“a patentee has brought what would otherwise be equivalents of a limitation into the literal scope of the claim, the doctrine of equivalents is unavailable to further broaden the scope of the claim.”).

So there were really two arguably very similar questions: (1) is 74.26% literally “about 80%” and (2) is 74.26% equivalent to 80% (and could Vertex resort to DOE). To properly conduct the analysis requires the use of the oft conflated but analogous doctrines of prosecution history disclaimer and prosecution history estoppel. As a reminder, prosecution history disclaimer is a claim construction issue, and means that the literal scope of the claim is narrowed. Prosecution history estoppel prevents the patentee from recapturing what was disclaimed or surrendered through the doctrine of equivalents.

Because of the fuzziness of “about,” applying these doctrines to this fact scenario gets quite hairy. For example, if an original claim recited exactly 72-88% and was rejected, and the patentee amended the claim to recite “80%,” it would be clear there was a narrowing amendment and both prosecution history disclaimer and estoppel would apply, with the claim limited to literally 80% and the patentee barred from trying to recapture alleged equivalents. However, when the original claims are “about 72 to about 88%” and amended to “about 80” it is not clear what scope was surrendered and thus what literal scope remains. For example, a patentee could argue that the patentee merely surrendered the literal scope of “about” below 72 and above 88, but still retained 72-88%. Or, a significant digits nerd like myself could take it even further and argue “about 80” is actually broader than “about 72 to about 88” because 80 has fewer significant digits and therefore provides less precision.

While Vertex didn’t make this specific significant figures argument as best I can tell, it did argue that “about 80” was actually broader than 72-88, covering at least 70-90%. At bottom, however, I think Vertex had no way to explain why it should be given scope either literally (with the about claims) or under DOE (for the exact claims) that the patent office rejected. Digging through the briefing, it appears Vertex attempted to argue the amendment was only “tangential” the alleged equivalent because the concern was directed particularly “at the upper bound of approximately 88%.” But if that were the case, why didn’t Vertex amend the claims to recite “about 72 to about 80%”?

It is unclear to me why Vertex appears to have argued for a broader range of 70-90% (both for literal scope of the about claims and for equivalence), rather than arguing that while 72% and below or 88% and above might have been surrendered and outside the scope of the claims, 74.3% was still literally covered by “about 80%” and was equivalent to 80%. Vertex made this point, but only when arguing for the tangential exception to PHE, stating “Critically, no specific intermediate value between about 72% and about 80%, and certainly not a composition at 74.3% amorphous ivacaftor, was ever identified, discussed, tested, or negotiated away during prosecution.”

While I do not think it changes the outcome, I think making this the key point of the argument (rather than buried in the tangential exception) was the only potential path to victory for Vertex. Having a literal range for “about 80%” (and an equivalence range for 80%) that was narrower than “about 72% to about 88%” would have been far more credible argument than asking the Judge to give a broader range than the one rejected by the patent office. The problem I think Vertex had is how can they provide a range that both avoids the 72-88% problem and covers 74.26% that is reasonably certain to a POSA based on the intrinsic record. And I think that’s where I end up full circle that “about” claims are inherently problematic, especially when used to avoid prior art, as it becomes increasingly difficult to justify a reasonably certain, broad claim scope. Indeed, if Vertex’s claims covered e.g., 70-90% ivacaftor, 18-25% HPMCAS, and 0.1-5% SLS, why not seek such claims?

So the clear takeaway to me is that while “about” can be used to attempt to broaden scope, it is no substitute for actually claiming the broader range and subjecting that broader range to prosecution.