Claim Construction: an International Convergence in Striking the Balance between Patent Protection and Legal Certainty

The US assessment of infringement in light of the DOE has given wide protection to patent owners.⁷ However, the situation seems to have changed significantly in recent years, given the growing limitations posed. The US DOE faces four major limitations, namely the prosecution history estoppel (PHE), the prior art, the all-limitation rule and the public dedication doctrine. The previous, broad application of DOE favoured patent owners, and in recent years, US courts have tried to establish a more balanced approach. However, as a result of these limitations, it seems that the DOE has almost been nullified.

Since Warner-Jenkinson,⁸ courts seem to give more importance to the claims in defining the invention, which provide notice to the public on the exact scope of the invention. Therefore, the percentage of success of infringements by equivalence is very low in the most recent times.⁹

However, in Festo,¹⁰ the USSC overturned the decision of the Court of Appeal for the Federal Circuit; the Court of Appeal had adopted a ‘complete bar’ approach to the PHE. The Supreme Court’s more flexible approach gives patentees a chance to rebut the presumption that amendments are done for patentability reasons. Nevertheless, in practice, patentees are still in a disadvantageous position given the arbitrariness of the Festo case’s presumption, and it appears that the doctrinal change caused more uncertainty than remedies.¹¹ In determining whether an estoppel applied to a voluntary amendment to bar the DOE, Festo considered whether a broader claim description was foreseeable at the time the amendment was made. The USSC held that if the equivalent of the subject matter at issue was disclosed in the field of the invention, then the broader claim description was foreseeable.¹² Thus, if the applicant did not draft a broader claim language when the option to do so was foreseeable, the presumption that the applicant chose to not pursue the available broader claim applied.¹³

After Festo, lower courts applied the new flexible approach, almost always considering the ‘foreseeability’ test as a rebuttal criterion. However, it is extremely difficult for the patentee to rebut the presumption. In Duramed Pharmaceuticals v Paddock,¹⁴ the Federal Circuit clarified that the invention to determine foreseeability ‘need only to have been known in the field of pharmaceutical compositions’. Affirming that this knowledge was already acquired as part of the prior art, the foreseeability rebuttal was rejected.

This approach appears inconsistent with the underlying principle of DOE to protect patentees from easy circumvention of the words of the claim. If the foreseeability criterion of equivalents were applied too rigidly, it would ignore the guidance of applying the DOE flexibly to preserve equivalents that are not surrendered during the prosecution, as stated in Festo.¹⁵ Moreover, in the more recent US Pemetrexed¹⁶ case, the Federal Circuit applied the tangential relation exception and allowed the patentee to recapture through the DOE the modified elements during the prosecutions, even though the claims were amended for patentability reasons. This shows the uncertainty around the correct application of the Festo rules.

Notably, during a Symposium held at University College London in November 2017, Judge Kate O’Malley from the US Court of Appeal discussed the impact of the PHE in the US and affirmed that patentees are generally bound by their actions during the prosecution. However, this statement significantly differed from the later US Lilly decision.¹⁷

Some academics¹⁸ argue that the US DOE is in decline, and this is due partially to the growing impact of the restrictions and of the importance given by the courts to the public, which should have notice of the exact scope of the patent. This shows a reconsideration of the DOE as necessary to incentivize technical progress. There is evidence that shows a correlation between the growing limitations and the increase of patents filed for new technologies.¹⁹ Others challenge this argument. Osenga argues that the death of the doctrine has been exaggerated. She affirms that avoiding the circumvention of the words of claims is still a major concern in the USA.²⁰

In conclusion, compared to the past, it is...