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Prosecution history estoppel (PHE), also known as file wrapper estoppel, is a legal principle relevant to defining the scope and limitations of the doctrine of equivalents in patent infringement disputes. The doctrine of equivalents allows patentees to act against non-literal infringement, where an accused product or process differs only in trivial or non-relevant ways. This way, third parties cannot avoid the liability of infringing a patent after performing modifications that would not lead to substantial changes, bearing that the concept of what would be relevant or not is another very rich discussion. PHE, in turn, can restrict the patentee’s right by deterring it from applying the doctrine of equivalents to recover subject matter removed from the literal scope of a claim during the prosecution. Approaches vary by jurisdiction, including the weight given to prosecution history in claim construction.

In Brazil, the PHE has already reached the Federal Courts. In the recent Janssen v. Cristália infringement lawsuit, Cristália (defendant) raised PHE to refute Janssen’s allegations that Darvyr® infringes patent PI 0311176-8, which covers the reference listed drug Prezista®.

Janssen alleged that, when comparing the subject matter of patent PI 0311176-8 with Darvyr: (i) both products contain darunavir; and (ii) darunavir propylene glycolate is equivalent to darunavir ethanolate. Cristália, in turn, argued that Janssen waived protection for darunavir propylene glycolate during the prosecution of PI 0311176-8 and, therefore, could not rely on the doctrine of equivalents to prevent its use.

PI 0311176-8 was filed with a broad set of claims, covering any pseudopolymorph of darunavir formed from alcohols of 1-4 carbons, including propylene glycol. Following enablement objections by the Brazilian FDA (ANVISA), Janssen limited the set of claims of PI 0311176-8 to darunavir ethanolate. According to Cristália, Janssen abandoned the other pseudopolymorphs by severely reducing the claimed scope of protection to secure grant. Otherwise, PI 0311176-8 would not have been granted. On this view, the prosecution history of PI 0311176-8 shows a clear waiver of protection for the other forms, including the propylene glycolate used in Darvyr, foreclosing equivalence-based infringement.

Janssen defended itself by arguing that they never abandoned the other pseudopolymorphic forms; they narrowed the claims merely to  expedite the prosecution. According to Janssen, although the principle of PHE establishes that exclusions made by the applicant in the set of claims can be used as defense by third parties in cases of alleged equivalence infringement, it should not be applied mechanically. In Janssen’s view, not every act or statement during the technical examination of a patent application allow the prosecution history to be argued as defense in an infringement lawsuit. One must assess whether the statements justified the patentability of a narrower claim and whether amendments overcame prior art objections made by the examiner. Where an argument bears no direct connection to cited prior art documents and was not at all critical to the granting, then such argument should be irrelevant in determining the scope of protection conferred by the patent claims. Thus, Janssen defended that, since the reduction in the scope of protection of PI 0311176-8 during the prosecution addressed enablement rather than prior art, PHE should not apply.

Although the court’s decision did not expressly address the PHE discussion, concluding that Cristália’s acts fell within the Bolar exception (Article 43, item VII, of the Brazilian Patent Statute), PHE is increasingly being used in Brazil as a defense strategy against the doctrine of equivalents. Alleged infringers not only obtain a detailed prosecution history of the disputed patent, but also inspect the file wrapper of patents of the same family in Brazil and abroad. Thus, patentees should exercise caution with the statements and amendments made during the prosecution, as PHE is posed to be increasingly relevant in litigation in Brazil.