Claim Terms Can Be Construed to Have More than One Meaning

May 20, 2013

What This Means To You

  • When using a claim term that can have more than one meaning depending on context, be sure to use it consistently within each context, especially when that context represents an improvement over the prior art.
  • By not providing numerical boundaries for a claim term, you may secure a broader construction of the term based on its ordinary and customary meaning.
  • This case provides precedent for a broad construction of the term “substantially pure.”


In Aventis Pharmaceuticals v. Amino Chemicals Ltd., the U.S. Court of Appeals for the Federal Circuit (Federal Circuit) confirmed that the claim term “substantially pure” can mean two different things depending on the context in which it is used. In this case, the term was used indiscriminately throughout the patent’s specification to refer to both intermediate compounds and a final drug product.

The Federal Circuit did not agree with the district court’s rule of “one construction throughout the patent,” noting that claims should be construed in light of the context in which they are used. The Court further noted that the same claim term can have different constructions within the claims and the specification.

Case Background

Amino Chemicals, a generic drug manufacturer, submitted Abbreviated New Drug Applications (ANDAs) to the FDA to market a generic form of fexofenadine, the active ingredient in the allergy medicine ALLEGRA®, exclusively licensed by Aventis. Aventis sued Amino for infringing on its patent for producing fexofenadine.

The district court found that the patent did not expressly define the term “substantially pure” and construed the term to mean that the intermediate compound was of pharmaceutical grade purity (98% pure with respect to all impurities). Based on this construction, Aventis stipulated that infringement could not be proven, and timely appealed.

Decision Analysis

In reviewing the construction of the term “substantially pure” with respect to a regioisomer (a particular form of an intermediate compound used in producing fexofenadin), the Federal Circuit disagreed with the district court’s reliance on statements made in an interference proceeding involving a related patent, in which “substantially pure” was regarded as pharmaceutical grade purity. The Court explained that the focus of that interference was interpreting the claims in reference to the end product, thus there was no justification for applying the definition to the term “substantially pure regioisomer” in the patent in dispute.

The Court also disagreed with the district court’s conclusion that “substantially pure” applied to all impurities, as opposed to regioisomeric impurities, stating that the lower court’s analysis did not consider the appropriate frame of reference for claim construction, namely, the improvement of the patented process over the prior art process.

After concluding that the district court erred in its claim construction, and without clear guidance from the claims, specification, or other intrinsic evidence, the Court applied the “ordinary and customary” definition to the claim term. In doing so, the Court adopted Aventis’ proposed construction of “substantially pure regioisomer,” as “largely but not wholly the para regioisomer,” as compared to the meta isomer.

The Court reasoned that the construction was previously applied with approval by the Court, and that “largely but not wholly” represented a flexible approach to defining purity for an intermediate, was consistent with the specification’s silence regarding numerical precision, and was not arbitrarily tied to the standards for pharmaceutical-grade end products.


In this case, the fact that Aventis did not provide numerical boundaries for the term “substantially pure” allowed for a broad construction of the term by the Federal Circuit, based on the ordinary and customary meaning of the term.

The dissenting opinion by Judge Bryson, however, would have adopted the district court’s construction, finding the evidence of what “substantially pure” meant in a related interference proceeding to be more meaningful in the absence of guidance in the patent in suit.

When a claim term can have more than one meaning depending on context, it is prudent to use it consistently within that context, especially when that context represents an improvement over the prior art.