The US Court of Appeals for the Federal Circuit reversed a district court’s summary judgment that found a patent was not obvious because the claimed pH range would not have been obvious-to-try despite overlapping ranges between the claimed pH range and the pH range for similar prior art compounds. Valeant Pharms. Intl. v. Mylan Pharms. Inc., Case No. 18-2097 (Fed. Cir. Apr. 8, 2020) (Lourie, J.).

Valeant owns a patent directed to stable methylnaltrexone pharmaceutical preparations that can be useful for reducing the side effects of opioids. Methylnaltrexone is unstable in aqueous solutions, but the inventors discovered that when the pH of the methylnaltrexone solution is adjusted to between 3.0 and 3.5, the percentage of degradants drops significantly. The patent is listed in the Orange Book for Relistor^®, an injectable drug used to treat constipation as a side effect of taking opioid medication.

Mylan filed an Abbreviated New Drug Application (ANDA), and Valeant responded by filing an infringement suit against Mylan. Mylan admitted infringement, but sought to invalidate various claims of the patent as obvious over solutions of similar anti-opioids. The district court granted Valeant’s motion for summary judgment of no invalidity, finding that the asserted claim would not have been obvious. In doing so, the district court rejected Mylan’s argument that a pH range of 3 to 4 would have been obvious-to-try because the prior art did not teach formulations of the claimed compound (only similar compounds), even though the prior art taught the claimed pH range. Mylan appealed.

The Federal Circuit reversed, finding that the district court erred in its obviousness analysis. The Court explained that the record supported a prima facie case of obviousness and that prior art ranges for solutions of structurally and functionally similar compounds that overlap with a claimed range can establish prima facie obviousness: “When compounds share significant structural and functional similarity, those compounds are likely to share other properties, including optimal formulation for long-term stability.” The Court concluded that the district court erred by rejecting the inference that a person of skill could expect similar stability of structurally and functionally similar molecules at similar pH ranges in solution as a matter of law at the summary judgment stage. The Court, however, was careful to note that its decision should not be misconstrued to mean that molecules with similar structure and function can always be expected to exhibit similar properties for formulation.

The Federal Circuit also found that the district court erred in its obvious-to-try analysis by concluding that there was not a finite number of options between pH ranges falling between 3 and 7 and none of the prior art identified pH as the “first variable” that a skilled artisan would consider. The Court disagreed, noting that the bounded range of pH 3 to 4 presented a finite number of narrower pH ranges for a skilled artisan to try and that pH was, in fact, the only variable in the asserted claim – not one of many variables that can be experimented with. The Court also explained that “there is no requirement that for a variable to be obvious to try, it must be the first variable a person of skill would alter.”