A Thin Gray Line: Reading Claims in Light of the Specification Versus Impermissibly Reading Limitations into the Claims

There is a fine and often ambiguous line between improperly importing limitations from the specification into the claims and interpreting claims in light of the specification.  The Federal Circuit recently drew that line in The Medicines Company v. Mylan, Inc., reversing a lower court’s judgment that Plaintiff Mylan’s proposed bivalirudin formulation would infringe U.S. Patent No. 7,582,727 (“the ’727 patent”) covering bivalirudin (ANGIOMAX®).  The Federal Circuit held that the district court erred by failing to read unrecited processing limitations into the claims based on statements in the specification.

The asserted claims are directed to pharmaceutical “batches” of bivalirudin having less than “a maximum impurity level” and a target pH that is “adjusted by a base.” The specification describes an “efficient mixing” process used to ensure consistency amongst batches, but that phraseology does not appear in the claims.  Mylan employs a different process than that described in the specification to ensure batch consistency and pH level in its API. Thus, the issue was whether the claims require “efficient mixing” even though that language is absent from the claims.  (Incidentally, the claims in a related patent asserted by Medicines did recite “efficient mixing,” and the district court held that Mylan did not infringe those claims.)

The Federal Circuit held that the claims do require this unrecited element.  First, the Federal Circuit reasoned that the claimed impurity level could not simply apply to individual batches because that was already known.  “Such a construction would render the claims of the ‘727 patent invalid in light of Medicines’ numerous pre-critical-date sales of ANGIOMAX® batches . . . .”

Next, the Federal Circuit considered the specification and prosecution history.  In describing the background of the invention in the specification, the applicants stated that the “development of a compounding process for formulating bivalirudin that consistently generates formulations having low levels of impurities is desirable.”  The applicants also referred to “the compounding process . . . of the invention,” thereby suggesting the process was an integral part of the invention.  The applicants buttressed this understanding during prosecution, when they again referred to “the new process of the present invention.”

The Federal Circuit looked to the specification to determine what process was required by the claims.   The court found the answer in the “efficient mixing” process described in “example 5,” as that was the only process described for achieving consistent impurity and pH levels. Thus, the Court construed a reference to “batches” as requiring the process described in the patent, which ultimately limited the claims to the process of a single example in the patent.

This case presents a conundrum often faced by district courts when construing claims:  whether and how to consider claim-limiting language found only in the specification. As noted by Judge Walkers in his dissent in Medegen MMS v. ICU Medical, Inc.:

We have had many occasions to cite one or both of the twin axioms regarding the role of the specification in claim construction: On the one hand, claims “must be read in view of the specification, of which they are a part.” On the other hand, it is improper to read a limitation from the specification into the claims. Although parties frequently cite one or the other of these axioms to us as if the axiom were sufficient, standing alone, to resolve the claim construction issues we are called upon to decide, the axioms themselves seldom provide an answer, but instead merely frame the question to be resolved.

 The good news is that litigants should have good arguments regardless of which side of the debate they find themselves on.