This week the Federal Circuit vacated and remanded a district court judgment of invalidity because the district court had incorrectly applied the inherency doctrine in the obviousness analysis.

The case, between Par and Twi, involved methods of use of nanosized formulations of the drug megestrol acetate. Par Pharm., Inc. v. TWi Pharms., Inc., No. 1:11-cv-02466 (D. Md. 2014). The patentee claimed to have discovered that using nanosized particles, as opposed to microsized particles, of megestrol resulted in a decrease food effect. The asserted claims were directed to methods of increasing body mass in a human using megestrol acetate wherein there was “no substantial difference” in C_max when given in a fed state or a fasted state.

The district court found the claims obvious. The court found that all elements of the claims were explicit in the prior art except for the food effect limitation. For that claim limitation, the court found that although not explicit in the prior art, it was an inherent property of the otherwise-obvious nanosized formulation.

On appeal, the Federal Circuit vacated and remanded based on the district court’s inherency finding. The Federal Circuit reiterated that inherency can be applied in an obviousness context, but held that its application is limited and must meet a high standard. Inherency, according to the Federal Circuit, can only apply to obviousness when the claim limitation is the “natural result” of the combination of prior art elements. In this case, the Federal Circuit found that, while there was evidence that nanosized particle would lead to a decreased food effect, there was no finding that it would necessarily result in “no substantial difference” between a fed and fasted state. According to the Federal Circuit, “[w]hile it may be true that a reduction in particle size naturally results in some improvement in the food effect, the district court failed to conclude that the reduction in particle size naturally results in ‘no substantial difference’ in the food effect.” The Federal Circuit vacated and remanded for consideration of whether TWi had shown, in fact, that the “natural result” of the prior art combination would be “no substantial difference” in Cmax.

This case serves as a guidepost to defendants mounting an obviousness defense based on inherency. Future defendants should be careful to support any inherency argument with evidence showing that the claim limitation was the natural result of the prior art combination and not merely a possible or even likely result.