The recent decision in Dow Chemical1 confirmed the Federal Circuit’s earlier position in Teva Pharma2, that in instances where multiple methods of measurement exist for a parameter, a patentee must make sure to tell the public which one is being used.

Nova Chemicals Corporation appealed a U.S. District Court decision in which Dow Chemicals was awarded supplemental damages in the form of lost profits and reasonable royalties, but denied enhanced damages, related to Nova’s infringement of two of Dow Chemical’s patents.3 In the period between the decision from the District Court and Nova’s appeal, the Supreme Court decidedNautilus.4 The Federal Circuit determined that it was appropriate to reopen their previous decision under the change of law exception for both law of the case and issue preclusion.5 Specifically, the Federal Circuit determined that Nautilus changed the law of indefiniteness,6 second that the prior decision applied pre-Nautilus law,7 and third that the original decision would have been different under the Nautilus standard.8

The claims at issue in the infringed patents were directed to ethylene polymer compositions having a series of characteristic properties. One of the properties was directed to the “slope of strain hardening coefficient” or “SHC” of the polymer compositions.9 While the patents defined how to calculate SHC, the mathematical formulation required that the “slope of strain hardening” be determined.10 Nova argued that the term “slope of strain hardening coefficient” was indefinite because the patents failed to teach, with reasonable certainty, where and how the “slope of strain hardening” was to be measured from the stress/strain curve of the polymer.11

The specifications of Dow’s patents taught that “[t]he slope of strain hardening” was calculated by drawing “a line parallel to the strain hardening region of the . . . stress/strain curve,” and both parties agreed that the slope was to be measured at its maximum value.12 However, the Federal Circuit found that at least four different methods existed to determine the maximum slope, with each providing “simply a different way of determining the maximum slope,” and each of which may produce a different slope calculation.1314 Thus, because the methods did not always produce the same results, the Federal Circuit stated concern that the method chosen for calculating the slope of strain hardening could affect whether or not a given product infringed the claims.15

The Federal Circuit also noted that, prior to Nautilus, the existence of multiple methods to determine a characteristic (such as the slope of a stress/strain curve) would not have rendered the claims indefinite.16 However, under the current law from the Supreme Court, claims would be found invalid for indefiniteness if, when “read in light of the specification . . . and the prosecution history, failed to inform with reasonable certainty, those skilled in the art about the scope of the invention.”17 As in their decision in Teva Pharms.18, the Federal Circuit cited the lack of a definition, in either the specification or file history, for the term at issue when multiple, different ways of measuring the term were known in the art and encompassed by the claims, as the reason for finding the claims indefinite.19

These two indefiniteness cases from the Federal Circuit highlight the need for including explicit definitions, or specifying the exact methodology employed, when the characteristic of a claimed product or process can be determined in more than one way. While Teva Pharms and Dow Chemicalrelated to chemical (molecular weight) and material (SHC) characteristics of a product, the lessons learned should also be applied to pharmaceutical and biotech patents. For example, if multiple methods exist for determining an end-point of an in vitro or in vivo pharmacology study (e.g., effective dose, or drug tissue concentration) it is important to specifically delineate and define which methodology is used, and how those determinations are made. Similarly, measurements related to characteristics of a bioprocess (e.g., impurity levels, protein production rate) should be carefully set forth and clearly outlined to ensure that they meet the “reasonable certainty” requirement that will be applied when determining if the claims are indefinite.20