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Editor's Note: This article was originally published in BullsEye, a newsletter distributed by IMS Expert Services.

What is the meaning of the word "about" when used in a patent? The Federal Circuit Court of Appeals confronted that elusive question in a recent dispute between two pharmaceutical manufacturers and expert testimony proved important in finding the answer.

But while the court accepted the experts' opinions on the meaning of "about" as used in the patent, it turned an about face and rejected their testimony as to the ultimate issue of infringement.

Ortho-McNeil Pharmaceutical brought the lawsuit against generic-drug maker Caraco Pharmaceutical Laboratories alleging infringement of its U.S. Patent No. 5,336,691. Ortho's patent covered a pain reliever composed from two well-known analgesics; tramadol and acetaminophen.

The patent disclosed that when combined in certain ratios the effects of the two drugs were heightened. At issue in the case was the patent's claim number 6, which covered a composition 'wherein the ratio of the tramadol material to acetaminophen is a weight ratio of about 1:5.'

Ortho sued after Caraco filed an Abbreviated New Drug Application disclosing its plan to make and sell its own composition containing tramadol and acetaminophen. Caraco said its drug would have an average ratio of tramadol to acetaminophen of 1:8.67 and of no less than 1:7.5. Ortho contended that Caraco's drug would infringe its patent.

The district court granted summary judgment and Ortho appealed to the Federal Circuit. Both in the district court and on appeal, the case focused on the proper construction of the term 'about 1:5.' Ortho contended that it encompassed a range of at least 1:3.6 to 1:7.1, and that, under the doctrine of equivalents, Caraco's formulation infringed. Caraco argued for a narrow construction.

The district court adopted the construction asserted by Ortho, construing 'about 1:5' to mean 'approximately 1:5, encompassing a range of ratios no greater than 1:3.6 to 1:7.1.' It reached this conclusion relying in part on the intrinsic evidence of the claim and the specification and, in part, upon the extrinsic evidence of Ortho's experts, Dr. Donald R. Stanski and Dr. Eric Smith. Both experts gave the opinion that one of ordinary skill in the art would conclude that the 'about 1:5' limitation would include a range of ratios that would extend up to and include 1:7.1.

The Federal Circuit affirmed this construction. Like the district court, it found support for this construction both in the claim itself and in the testimony of Ortho's expert, Dr. Stanski. 'Dr. Stanski opined that 'about 1:5' means 'about 1:5, which includes a ratio up to and including 1:7.1',' the court noted.

Accepting this construction meant that Caraco's product did not literally infringe Ortho's patent. Ortho's patent covered a ratio of up to 1:7.1, while Caraco's started at 1:7.5. The question, therefore, became whether Caraco's drug infringed under the doctrine of equivalents.

Relying on its experts, Ortho asserted it did. One expert, Dr. Stanski, opined that a weight ratio of 1:8.76 is substantially similar to a weight ratio of 1:5. The other expert, Dr. Smith, stated in his report that the 'degree of synergy of a composition with a weight ratio of tramadol to acetaminophen of 1:5 is similar to the degree of synergy of a composition with a weight ratio of tramadol to acetaminophen of 1:8.67.'

But the district court disagreed. It concluded that finding infringement by a formulation with an average weight ratio of 1:8.67 would render meaningless the 'about 1:5' limitation.

The Federal Circuit affirmed, finding that the 1:5 parameter was critical to the invention. Stretching the bounds of that parameter to cover Caraco's drug would directly conflict with the patent's express claim to both the 1:1 and the 1:5 ratios, the court said.

'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 court said. 'The intrinsic evidence points to the desirability, and thus the criticality, of the 1:5 ratio versus other ratios.'

'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,' the court continued. 'We agree with the district court that to do so would eviscerate the limitation.'

For these reasons, the court said, it concluded that Caraco's drug could not infringe Ortho's patent and that the district court properly granted summary judgment of non-infringement.

Ortho-McNeil Pharmaceutical, Inc. v. Caraco Pharmaceutical Laboratories, Ltd., Case No. 06-1102 (Fed. Cir. Jan. 19, 2007).