Last month, the Federal Circuit affirmed the district court’s granting of a preliminary injunction (PI) precluding Aurobindo from marketing its proposed isosulfan blue (ISB) product in the U.S. The district court originally based the PI on three patents: two process patents and one product patent. The Federal Circuit affirmed the PI based only on the product patent. Was affirming the PI on only the product patent the right thing to do? Let’s see.

Background

All three patents have the same disclosure. The two process patents claim processes for making ISB which include using silver oxide (AgO). The claimed processes reportedly allow for the production of highly pure ISB (>99%). The product patent claims ISB having >99% purity.

In contrast, Aurobindo uses manganese dioxide (MnO2) to produce ISB having 95% purity, which is further purified by HPLC to obtain a product having >99% purity.

District Court

Aurobindo argued to the district court that it does not infringe the two process patents under the doctrine of equivalents because it uses MnO2. Nevertheless, the district court found that Mylan would likely have success proving Aurobindo infringes the two process patents because AgO and MnO2 are equivalent under the function-way-result (FWR) test. The district court did not apply the “insubstantial differences” test.

Aurobindo did not argue that it does not infringe the product patent. Rather, Aurobindo argued that the product patent is invalid (1) over prior art and (2) as indefinite. The district court found that Aurobindo would not likely have success proving that that the product patent is invalid.

The district court then granted a PI based on all three patents.

Federal Circuit

The Federal Circuit found that the district court erred when analyzing the “way” portion of the FWR test – the district court did not properly compare the “way” in which MnO2 and AgO convert a precursor compound to ISB. The Federal Circuit also suggested that the non-applied “insubstantial differences” test might be more appropriate than the FWR test in chemical cases. Accordingly, the Federal Circuit did not affirm the PI based on the two process patents.

The Federal Circuit affirmed the PI based on the product patent, finding that the district court did not err in its invalidity analysis. In particular, the Federal Circuit relied upon Aventis for the proposition that “a purified compound is not always prima facie obvious over the prior art mixture if the process to arrive at the purified compound is itself of patentable weight,” and noted that the district court “expressly relied upon the Aventis proposition in making its determination.”

Analysis

As noted by the Federal Circuit, a PI based on infringement under the doctrine of equivalents is “unusual” given that “equivalents cases are highly factual inquiries that rarely come clear on a premature record.” So, in that sense, it is not surprising that the Federal Circuit did not affirm the PI based on the process patents.

Maintaining the PI based on the product patent is more troubling, though. The Federal Circuit and district court both relied upon Aventis (a process, if “of patentable weight,” can help render a purified compound non-obvious). But the problem is that the product patent claims do not appear to be limited to the process “of patentable weight” using AgO. Rather, the product patent broadly claims any product having >99% purity (made by any process).

The Federal Circuit also noted that “it is clear from the record here that, although ISB was known in the prior art, the path to arrive at ISB with a purity of greater than 99.0% was not known before the relevant date” of the product patent.

Perhaps the most troubling aspect here is that the product patent broadly claims ISB made from any process having purity >99% when it apparently discloses one way to produce such purified ISB (using AgO) and when previous methods of producing ISB failed to achieve such purity. But this may relate more to lack of enablement of the claims than obviousness, and enablement does not appear to have been an issue at the PI stage. Maybe it will be at trial.