Applying prosecution history estoppel in patent infringement cases

A judgment issued by Section 28 of the Madrid Provincial Court (an appeal court) on 1st December 2008 has welcomed and confirmed the application in Spain of the limit known as prosecution history estoppel to the doctrine of equivalents in patent infringement cases. Unlike the courts of the United States, Spanish courts have disagreed over whether prosecution history estoppel must be taken into account when applying the doctrine of equivalents. The decision also confirmed the landmark decision issued by Section 15 of the Barcelona Provincial Court on 17th January 2008 (the Olanzapine Case), where the court considered the history of the patent and the patentee’s intentions during the examination process (ie, prosecution history estoppel) in a case concerning an infringement of Eli Lilly’s patent by equivalence.

In patent infringement cases the application and construction of the doctrine of equivalents that is used to determine whether the realisation at issue infringes the claims of the patent put forward by the plaintiff is crucial. The relevance of the doctrine of equivalence derives from the fact that most realisations do not literally infringe patents - they are not exact copies of the claims of the patent, but rather copies with certain differential aspects that have been included to distinguish themselves from the claims of the relevant patent. Thus, Article 69.1 of the European Patent Convention (EPC) - and now of the EPC 2000, which came into force on 13th December 2007 - provides that: “for the purpose of determining the extent of protection conferred by a European patent, due account shall be taken of any element which is an equivalent to an element specified in the claims.”

Even though all EPC contracting states apply the doctrine of equivalents to grant protection beyond the precise wording of patent claims, the national courts use different tests to decide what is equivalent. In Germany, for example, the courts have used several tests: 

  • the problem-solving approach (Bierklärmittel, 1984); 
  • an interpretation based on function (Spannschraube, 1999); 
  • the obviousness test (Formstein, 1986); and 
  • the subjective approach (Broadcasting Radio System, 1988).

For their part, the French courts use the double identity substantial test (ie, whether the invention performs substantially the same function and obtains the same result, irrespective of the manner in which this is achieved); while in the United Kingdom, the courts rely on the three-question test. Following experiences using other tests, the Spanish courts have imported the three-question test for pharmaceutical and chemical patent cases. The three-question test is a construction derived and directly influenced by UK (Improver, 1990) and German (Formstein, 1986) case law, and comprises the following questions: 

  • Does the variant introduced have a substantial effect on the functioning of the invention? If so, there is no equivalence; if not (ie, functioning is not altered), question two is asked. 
  • Would such variant have been obvious at the date of publication of the patent to a person skilled in the art? (Catnic, 1982). If the variant introduced was not obvious (ie, was inventive), there is no equivalence; if it was obvious, question three is asked. 
  • Would a reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the literal wording of the claim was essential for the invention? If the answer is no, the variant infringes the patent.

In Spain, the third question has been reformulated to read: “Would a reader skilled in the art nevertheless have understood from the language of the claim that such variation was an object of the patent?” This third question links to the prosecution history estoppel limit and the role of the inventor’s intention in defining the scope of patent protection. The test has been applied in regard to chemical and pharmaceutical patents in the Olanzapine Case decisions (the judgment issued by Section 15 of the Barcelona Provincial Court on 17th January 2008, which upheld the judgment issued by the Barcelona Third Mercantile Court on 16th October 2006).

The risk of contradictory judgments being issued in different EPC countries in the same patent infringement case, depending on which test is applied, is further increased by the fact that there is no uniformity in regard to whether the prosecution history estoppel limit must be applied to the doctrine of equivalents.

This limit, which was first set out in a US case (Festo, 2002), provides that the patentee’s intention during the examination process is relevant in determining the scope of protection of the patent – that is, remarks made and acts carried out during the examination process must be considered when interpreting patents. Thus, subject matter renounced or limited by the patent applicant during the examination process, of its own initiative or at the examiner’s request in order to overcome any objection to the invention’s patentability, is not protected by the patent. This adds a subjective element to the analysis: the patentee’s intention is relevant in ascertaining the scope of protection of a patent.

The judgment issued on 1st December 2008 by Section 28 of the Madrid Provincial Court confirmed the application of the doctrine of prosecution history estoppel by the Spanish courts. This judgment also helped to clarify certain points that must be taken into account when analysing the history of a patent, such as the fact that: (i) not all amendments to the wording of the claim made during the examination process necessarily imply a restriction to the object of the invention; and (ii) if the amendments do restrict the object of the claims, not all of them result from a demand to comply with the patentability requirements, although this is the usual explanation for a restriction on the object of the invention being introduced during the examination process. Consequently, the burden of proof will rely on the plaintiffs arguing that the restrictions made during the examination process to their claims were not a result of any patentability requirements condition.

Moreover, the appeal court’s judgment goes one step further by considering it unacceptable for the plaintiff to invoke the doctrine of equivalents in order to include in the protected scope of the patent technical characteristics that could have been considered within its object, but that were expressly excluded by the same plaintiff during the examination process. This is a fundamental expression of the doctrine of prosecution history estoppel and of the Spanish equivalent of that doctrine: the own acts doctrine, which the Supreme Court defines as “a limit to the exercise of a subjective right or of an ability, derived from the good faith principle and, particularly, of the demand of observing a coherent behaviour in the legal traffic”, so that “if there is an incompatibility or contradiction between the prior conduct and the later pretension, according to the good faith principle, it would have to be attributed to the prior conduct” (Supreme Court judgment of 3rd November 1990).

Clearly, through this decision and recently issued case law, the Spanish courts are adopting a similar approach to that taken by the courts of other EPC countries, and are shedding some light on essential issues that often arise in patent infringement cases, such as how to define the scope of patent protection and where the limits to the subjective interpretation of patent claims lie.


This is an insight article whose content has not been commissioned or written by the IAM editorial team, but which has been proofed and edited to run in accordance with the IAM style guide.

Get unlimited access to all IAM content