The '691 patent has fifteen claims directed to a pharmaceutical composition comprising certain weight ratios of two known drugs, tramadol and acetaminophen. '691 Patent, col.11 l.18 to col.12 l.36. Both of these drugs act as pain relievers, i.e., analgesics. The '691 patent discloses that where these components are in certain ratios the pharmacological effects of the compositions are superadditive or synergistic. Id. Abstract. More specifically, the description of the invention reads:

The [acetaminophen] and the tramadol material are generally present in a weight ratio of tramadol material to [acetaminophen] from about 1:1 to 1:1600. Certain ratios result in a composition which exhibits synergistic analgesic effects. For example, in a composition comprising a tramadol material and [acetaminophen], the ratio of the tramadol material: [acetaminophen] is preferably from about 1:5 to 1:1600; and, more preferably, from about 1:19 to 1:800.

The most preferred ratios are from about 1:19 to 1:50. Compositions of a tramadol material and [acetaminophen] within these weight ratios have been shown to exhibit synergistic analgesic effects. In addition, the particular compositions wherein the ratio of the components are [sic] about 1:1 and about 1:5 are encompassed by the present invention.

Id. col.3 l.63 to col.4 l.8.

The only claim at issue is claim 6, a dependent claim, which, when read in conjunction with the two claims upon which it depends, states: "[A pharmaceutical composition comprising a tramadol material and acetaminophen], wherein the ratio of the tramadol material to acetaminophen is a weight ratio of about 1:5." Id. col.11 ll.19-34. As will be seen, the only claim construction dispute between the parties is the meaning of the phrase "about 1:5." The term "about" is used in all of the claims of the '691 patent to modify the weight ratios claimed therein. Id. col.11 l.19 to col.12 l.36.

Caraco's ANDA expressly required Caraco's formulation to have a weight ratio of no less than 1:7.5. Caraco moved for summary judgment of non-infringement, because its weight ratio was outside what it considered Ortho's patented range.

Under either claim construction, Caraco argued its ANDA-defined product did not literally infringe. With respect to infringement under the doctrine of equivalents, Caraco argued that the doctrine should not apply to broaden the scope of the "about 1:5" limitation beyond the range of ratios suggested by the confidence intervals in the patent because to do so would, alternatively, improperly expand a narrow claim limitation, improperly eliminate the 1:5 claim limitation, or improperly encompass the prior art disclosed in U.S. Patent No. 3,652,589 to Flick, et al. ("the Flick patent"). At argument in the district court, Caraco also stated that prosecution history estoppel should apply because, during reissue proceedings relating to the '691 patent, Ortho narrowed the "about 1:5" limitation to something very close to 1:5 when Ortho described the 1:5 limitation and clearly distinguished it from the 1:10 limitation disclosed in the Flick patent.

The district court construed the "about 1:5" limitation of claim 6 to mean "approximately 1:5, encompassing a range of ratios no greater than 1:3.6 to 1:7.1." In reaching this conclusion, the district court relied upon both intrinsic and extrinsic evidence. The intrinsic evidence upon which the district court relied included the claims and the specification. The extrinsic evidence upon which the court relied consisted, in part, of the opinions of Ortho's experts...

Ortho got a reissue, in the prosecution of which Ortho argued over the Flick patent, bolstering Caraco's contention.

Under its construction, the district court concluded that Caraco's ANDA-defined product did not literally infringe the '691 patent. In addition, the district court decided that there was no infringement under the doctrine of equivalents. Relying on the doctrine of claim vitiation, see Freedman Seating Co. v. Am. Seating Co., 420 F.3d 1350, 1362 (Fed. Cir. 2005), the court concluded that finding infringement by Caraco's formulation with an average weight ratio of 1:8.67 would render meaningless the "about 1:5" limitation. The court thus rejected Ortho's claim of infringement under the doctrine of equivalents.

The CAFC on "about":

This court has looked at the meaning of the term "about," and similar qualifying words or phrases, in other cases and has developed an approach to the interpretation of such terms:

[T]he word "about" does not have a universal meaning in patent claims, . . . the meaning depends upon the technological facts of the particular case.

The use of the word "about," avoids a strict numerical boundary to the specified parameter. Its range must be interpreted in its technological and stylistic context. We thus consider how the term . . . was used in the patent specification, the prosecution history, and other claims. It is appropriate to consider the effects of varying that parameter, for the inventor's intended meaning is relevant. Extrinsic evidence of meaning and usage in the art may be helpful in determining the criticality of the parameter . . . .

Pall Corp. v. Micron Separations, Inc., 66 F.3d 1211, 1217 (Fed. Cir. 1995) (citations omitted). See also Modine Mfg. Co. v. United States Int'l Trade Comm'n, 75 F.3d 1545, 1554 (Fed. Cir. 1996) (stating that "the usage [of the term 'about'] can usually be understood in light of the technology embodied by the invention"); Conopco, Inc. v. May Dep't Stores Co., 46 F.3d 1556 (Fed. Cir. 1994) (discussing the criticality of the claimed ratio to the invention and whether or not one of ordinary skill in the art would have read the modifier "about" expansively in light of the intrinsic evidence).

The appeals court concurred with the district court on both the intrinsic and extrinsic evidence, and thus confirmed the non-infringement decision. "About" was bounded for the purpose of determining non-infringement under the doctrine of equivalents.

Under the district court's claim construction, with which we agree, there can be no literal infringement because Caraco's formulation must have a weight ratio of tramadol to acetaminophen of no less than 1:7.5. The issue we must decide then is whether the district court erred in granting summary judgment of non-infringement under the doctrine of equivalents. The district court determined that a holding that Caraco's product infringed claim 6 of the '691 patent under the doctrine of equivalents would impermissibly vitiate the limitation of claim 1 of a weight ratio of tramadol to acetaminophen of "about 1:5." We see no error in that determination.

As discussed above in connection with claim construction, the 1:5 parameter was critical to the invention. Moreover, the '691 patent points out the 95% confidence levels and makes them relevant to determining the scope of the invention. An infringement analysis that stretches the bounds of the "about 1:5" limitation beyond those confidence intervals directly conflicts with the patent's express claim to both the 1:1 and the 1:5 ratios. The patent specification distinctly identifies the 1:5 ratio versus all the other ratios or ratio ranges. Under this circumstance, whether or not the 1:5 ratio's analgesic response is statistically different from that of other ratios is of no moment. The intrinsic evidence points to the desirability, and thus the criticality, of the 1:5 ratio versus other ratios.

Also relevant is the prosecution history of the '691 patent and the '221 reissue patent, described above. Ortho admitted that it claimed more than it was entitled to claim in the '691 patent when, in its reissue application, it cancelled the broader "comprising" claims, except for claim 6. In sum, having so distinctly claimed the "about 1:5" ratio, Ortho cannot now argue that the parameter is broad enough to encompass, through the doctrine of equivalents, ratios outside of the confidence intervals expressly identified in the patent. We agree with the district court that to do so would eviscerate the limitation. The intrinsic evidence in this case points to the criticality of the "about 1:5" parameter, which necessitates a narrow claim construction and range of equivalents that does not encompass Caraco's product.