In Mylan Institutional LLC et al. v. Aurobindo Pharma Ltd. et al., 2017-1645 (May 19, 2017), the Federal Circuit attempted to clarify the application of the doctrine of equivalents in chemical cases. Although affirming a district court grant of a preliminary injunction on a patent directed to isosulfan blue (ISB), a dye used for lymph node mapping, the court reversed the grant of the injunction to the extent it was based on two process patents. According to the Federal Circuit, the district court erred in determining that Mylan had demonstrated a likelihood of success in showing that Aurobindo infringes U.S. Patent 7,622,992 (the ’992 patent) and U.S. Patent 8,969,616 (the ’616 patent) because “the district court’s analysis of equivalence in this case was flawed.” Slip opinion at 12.

The ’992 and ’616 patents claim a process for preparing ISB comprising reacting isoleuco acid with silver oxide, recovering the ISB acid and treating the ISB acid with a sodium solution. Aurobindo’s process (the accused process) for preparing ISB differs from the patented process in that manganese dioxide is used in place of silver oxide as an oxidizing agent. The district court found that the accused process likely infringed the patented process under the doctrine of equivalents. Aurobindo argued on appeal that the district court erred, because manganese dioxide is a strong oxidizing agent that requires use of an acid, whereas silver oxide is a weak oxidizing agent that does not require an acid. Thus, according to Aurobindo, manganese dioxide and silver oxide oxidize isoleuco acid in different ways. Mylan countered, arguing that in the context of the process patents, silver oxide and manganese dioxide are equivalent. Mylan supported its assertion with expert testimony that the crude ISB yield from both the silver oxide and manganese dioxide processes is similar, a result that Mylan contended would not be expected if silver oxide and manganese dioxide were substantially different.

The Federal Circuit first noted that the “law on the doctrine of equivalents as applied to chemical materials is not clear, and its misapplication can lead to unsound results.” Id. Agreeing that the Supreme Court, in Graver Tank & Mfg. Co. v. Linde Air Prod. Co., 339 U.S. 605, 608, 609 (1950), had identified the function-way-result (FWR) test and the insubstantial differences test as two reasonable bases for an equivalence analysis, the Federal Circuit further acknowledged that the later case of Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 39 (1997) stated that “non-mechanical cases may not be well-suited to consideration under the FWR test. That seems to be particularly true in the chemical arts.” Slip opinion at 13. The Federal Circuit noted, however, that Warner-Jenkinson Co. also indicates that “the suitability of the two tests may vary, depending on the circumstances of the case[,]” and that “[d]ifferent linguistic frameworks may be more suitable to different cases, depending on their particular facts.” Id. (quoting Warner-Jenkinson Co., 520 U.S. at 40). Thus, the Federal Circuit concluded that the Supreme Court “seemingly blessed two equivalents tests, leaving to the lower courts in future cases the choice of which to apply.” Slip opinion at 13.

Some of the difficulty in applying the FWR test in chemical cases arises, according to the Federal Circuit, because it is applied on a limitation-by-limitation basis, and with “chemical compositions having many components, chemical compounds with many substituents (which are usually claimed as separate limitations), and those having a medical or biological use, it is often not clear what the ‘function’ or ‘way’ is for each claim limitation.” Id. at 14. The Federal Circuit further explained that in chemical process claims, the “function” and “way” of a claim limitation “may remain vague and often overlap[,]” or “may be synonymous.” Id. at 15. The Federal Circuit further implied that the “result” prong of the FWR test may be of limited use in chemical cases because, although “the structure and uses of one compound may be directly compared with those of another[,]” infringement under the FWR test is determined on a limitation-by-limitation basis. Id. at 14.

The Federal Circuit concluded that the district court’s application of the FWR test was flawed because the district court failed to properly address the “way” prong of the FWR test. Although the district court correctly identified oxidation of isoleuco acid as the function of silver oxide in the patented process, it dismissed as irrelevant, under either the FWR or insubstantial differences tests, Aurobindo’s argument that the oxidation strength of silver oxide is different from that of manganese dioxide. In the district court’s view, the absence of any claim limitation on oxidation strength rendered the relative oxidation strengths irrelevant. According to the Federal Circuit, the district court either failed to analyze the “way” prong of the FWR test or, if it did analyze “way,” failed to account for the relative oxidation strengths of silver oxide and manganese dioxide or the use of acid when using manganese dioxide. Thus, the Federal Circuit concluded “there is room for sufficient doubt as to whether silver oxide and manganese dioxide oxidize isoleuco acid in the same way so as to satisfy the ‘way’ prong of the FWR test.” Id. at 16.

The Federal Circuit recommended that in trying the merits of the case, the district court consider whether the insubstantial differences test might be better suited to evaluating the equivalence. The court stated that “[e]ven if evaluating the ‘function’ and ‘way’ prongs is feasible, the FWR test may be less appropriate for evaluating equivalence in chemical compounds.” Slip opinion at 16-17.

The Federal Circuit used a comparison between aspirin and ibuprofen in an attempt to demonstrate how “a compound may appear to be equivalent under the FWR test, but not under the substantiality of the differences test.” Id. at 17. The court first noted that due to the compounds’ substantial structural differences, “chemists would not usually consider [aspirin and ibuprofen] to be structural equivalents under the insubstantial differences test.” Id. On the other hand, the FWR test would suggest that aspirin and ibuprofen are substantial equivalents, according to the Federal Circuit, because “each provide[s] analgesia and anti-inflammatory activity (‘function’) by inhibiting prostaglandin synthesis (‘way’) in order to alleviate pain, reduce fevers, and lessen inflammation (‘result’).” Id. In this example, however, the Federal Circuit does not identify the claim in which the aspirin or ibuprofen appears, and so it provides no context against which equivalence of aspirin and ibuprofen is to be evaluated.[1]

The court further noted that “the process patents recite a method for preparing a specifically named compound by combining another specifically depicted compound with a third specific compound, viz., silver oxide. Each of these compounds is expressly named, and an infringement analysis must not take lightly the specific recitation of these materials.” Slip opinion at 17. The Federal Circuit further explained that “[m]anganese dioxide and silver oxide are substantially different in many respects. For example, manganese and silver are in different groups of the Periodic Table. In oxide form, manganese has an oxidation state of +4, while silver is +1. Those differences may well be relevant to equivalence at trial.” Id. at 18.

The court’s vague warning against taking lightly the recitation of specific materials, combined with its out-of-context, structure-based comparison of aspirin and ibuprofen, seems to suggest a focus on structural differences in chemical cases. If structural differences between two chemical compounds were sufficient to establish substantial differences and thus nonequivalence, however, then the doctrine of equivalents would appear to be quite limited, given that structural differences will necessarily exist between two nonidentical chemical compounds. Instead, it is likely that the context in which the chemical compound is claimed will guide assessment of whether a structural difference is substantial. For example, the structural differences between silver oxide and manganese dioxide that the court identifies as substantial, i.e., being in different groups in the periodic table and having different oxidation states, pertain to the different strengths of the compounds in the context of their use as oxidizing agents. As the court noted, a properly conducted FWR analysis would have taken into account these different oxidizing strengths as part of analyzing the “way” prong. In this case, therefore, it would appear that the FWR and insubstantial differences tests may in fact lead to the same conclusion.

In view of this case, the practitioner would be advised to assess equivalence in chemical cases under both the insubstantial differences test and the FWR test and, if needed, be prepared to justify the use of one test over the other. The context in which the limitation (e.g., chemical compound or structural substituent) is claimed and its function in the disclosed utility of the invention will be important.