Patent prosecution is an iterative process and it is during this process that the applicant often changes the language of their proposed claims. The doctrine of prosecution history estoppel, formerly known as file wrapper estoppel has been defined as an equitable tool for determining the scope of patent claims. This occurs when an inventor amends the patent application by narrowing the claims during the course of patent prosecution to overcome a rejection. It has received a great deal of attention from the courts recently. The innovators and competitors are left without a clear indication of what is and is not covered by a patent.

Prosecution history estoppel dictates that the claims must be interpreted in the light of their rejections, cancellations and amendments. These type of estoppels clearly exist in the face of a prior art rejection, but can also exist when the inventor makes representation in a writing that will cause the examiner to rely on those representations when it grants a patent based on the patent application. Arguments that are made during prosecution give rise to estoppels. If the arguments indicate a surrender of subject matter, then that subject matter may not be recaptured under the doctrine of equivalents litigation. Thus, the prosecution history estoppel is rooted in order to strengthen the public notice function of patents.

However, if a patentee amends the claims for a reason which is not related to patentability, prosecution history estoppel will not apply. Indeed, in addition to the amendments which are made to overcome the prior art, prosecution history estoppel applies to amendments that were made to overcome the rejections that are related to 35 U.S.C. § 101 and 35 U.S.C. 112. In any case if the patentee feels that the patent examiner has incorrectly rejected a claim on prior art grounds, the court will review the reason for the objection and the manner in which the amendments have been addressed or avoided. The examiner will however not look into the correctness of that objection. Thus the prosecution history estoppel can sometimes be a daunting barrier for a patentee to overcome. It is often required that the practitioners draft more narrow and specific claims which can be easily understood and interpreted.  However, if the claims are narrowly drafted, it becomes very difficult for a patentee to claim patent infringement.

Authored by Aishwarya Narayan

Contributed by Patent Prosecution Division of BananaIP in India

For further information on patent prosecution strategies in India, write to contact@bananaip.com