Addressing claim construction of a term used in several different contexts in the asserted patent claims, the U.S. Court of Appeals for the Federal Circuit reversed a stipulated non-infringement judgment entered by a district court after claim construction and explained that the term in dispute (“substantially pure”) could  have different constructions depending upon how the term is used within the claims and specification.  Aventis Pharmaceutical Inc.  v. Amino Chemicals Ltd., Case Nos. 11-1335, -1336 (Fed. Cir., May 20, 2013) (Reyna, J.) (Bryson, J., dissenting). 

The patent at issue concerns methods for making purer forms of piperidine derivatives, which are useful as antihistamines, and covers a method used to produce fexofenadine, the active ingredient in the allergy medicine Allegra®.  The patent is assigned to Albany Molecular Research and exclusively licensed by Aventis.  The defendants in the case, including Amino Chemicals, Dipharma, Mylan and Teva, are generic drug manufacturers.   At issue was the meaning of the phrase “substantially pure” recited in the claims to characterize an intermediate compound formed during the process.  The claims include the step of providing a “substantially pure regioisomer” of a particular structural formula, and then converting the substantially pure regioisomer to a piperidine derivative product.  The term “substantially pure” is not defined in the specification, and the specification fails to attach a numeric value to the substantially pure regioisomer.

The district court concluded that since the patent specification used the phrase “substantially pure” to describe both the regioisomer intermediate as well as the piperidine end product, its meaning must apply equally to both compounds.  In its construction, the district court relied upon statements in the prosecution history (of both the patent and a related patent) which indicated the inventor’s understanding of the term “substantially pure” to equate to a purity of 98 percent, i.e., pharmaceutical-grade purity with respect to all impurities.   Aventis appealed.

The Federal Circuit reversed, explaining that claims must be construed in light of the appropriate context in which the claim term is used.  The Federal Circuit noted that the district court’s construction conflated the purity required for the final product (i.e., for human consumption) with that of the piperidine intermediate. The Court further found that the “one construction throughout the patent” rule adopted by the district court was incorrect, stating that “there is no requirement that a claim term be construed uniformly, particularly if it would lead to a “nonsensical reading”.  The Court further reasoned that the district court improperly decoupled “substantially pure” from “regioisomer” in its construction, recognizing that there was no justification for applying a pharmaceutical-grade purity requirement of an ingested end product to an intermediate formed in the process.  Finally, in turning to the meaning of “substantially pure” in reference to the intermediate, the Court adopted the term’s ordinary and customary definition, citing cases in which “substantially” was interpreted as a non-specific term of approximation that avoids a numerical boundary.