Skip to main content

Effect of A Restriction Requirement on Prosecution History Estoppel

The decision whether to issue a Restriction Requirement during patent prosecution lies with the patent examiner, not the patent applicant.  A Restriction Requirement can nevertheless trigger prosecution history estoppel that limits the scope of an applicant’s issued claim.  The Federal Circuit’s recent decision in UCB, Inc. v. Watson Laboratories Inc. helps show how this situation can happen and how applicants can help prevent an examiner’s decision from adversely affecting patent scope.

In general, the doctrine of equivalents allows for patent infringement when a product, process, etc. does not literally infringe a claim but is an equivalent of the claimed invention.  Prosecution history estoppel is one way that a claim’s scope may be limited by preventing application of the doctrine of equivalents.  As stated in UCB, this limiting can occur because “[i]f a patentee surrenders certain subject matter during prosecution, the patentee is then barred from using the doctrine of equivalents to recover for infringement based on that same subject matter.”  (Quoting Power Integrations, Inc. v. Fairchild Semiconductor Int’l Inc.)  Prosecution history estoppel is typically applicable either by the applicant making a narrowing claim amendment during prosecution or making statements during prosecution that are a “clear and unmistakable surrender of the subject matter.”

During prosecution of the patent at issue in UCB, the examiner issued a Restriction Requirement between two groups of claims, Group I (claims 18-33) and Group II (claims 34-41).  The examiner explained the basis of restriction as being because the Group II claims “required use of PVP [polyvinylpyrrolidone] as a solubility enhancer, but PVP would only be required for a silicone-based polymer, not acrylate-based polymer,” so “‘the process of group II [was] only applicable on silicone-based polymer and not on acrylate-based polymer,’ while ‘group I read[] on a matrix based on acrylate polymer or silicone polymer.’”  (Brackets original in UCB.)  The applicant elected Group I.

In litigation the potential infringer argued that the election of Group I should prevent the claims from encompassing anything other than an acrylate polymer or silicone polymer due to prosecution history estoppel limiting the application of the doctrine of equivalents.  The Federal Circuit disagreed.

The Federal Circuit stated that “[a] restriction requirement does not necessarily invoke prosecution history estoppel,” implying that sometimes it may.  Quoting Merck & Co. v. Mylan Pharm., Inc., the Federal Circuit stated that “[w]hether a patentee’s actions in the face of a restriction requirement give rise to estoppel must be judged ‘from the viewpoint of a [skilled artisan], and when the issue includes consideration of formalities of patent practice, experience in patent law and procedures is presumed.’”  (Brackets original in UCB.)

The applicant did not make any amendment regarding the acrylate polymer or silicone polymer after issuance of the Restriction Requirement.  The Federal Circuit thus concluded that the applicant did not make a narrowing amendment so as to invoke prosecution history estoppel.  Additionally, the Federal Circuit stated that even if the applicant had made an amendment to generically recite an “adhesive” instead of either of the more particular acrylate polymer or silicone polymer, prosecution history estoppel would not have necessarily precluded application of the doctrine of equivalents to encompass an adhesive other than an acrylate polymer or silicone polymer because the examiner’s basis for restriction would have still remained.  The court’s doctrine of equivalents analysis did not end here since UCB involved numerous other issues related to invalidity under 35 U.S.C. §§ 102, 103, but these issues are beyond the scope of this article.

The decision in UCB helps highlight that while an examiner’s decision to issue a Restriction Requirement may in some circumstances lead to prosecution history estoppel preventing a later application of the doctrine of equivalents, it is not an automatic danger sign that future claim scope will be limited.

Subscribe To Viewpoints


Christina Sperry is a Mintz patent attorney who drafts and prosecutes patents for clients in the electrical, mechanical, and electro-mechanical fields. She represents companies and academic institutions in the medical technology field and helps protect patent innovations for medical and surgical devices.