• Amending a patent should not be confused with amending a patent application.Legal Law Justice image by Stacey Alexander from Fotolia.com
  
  It is important to distinguish between amending a patent that has already issued, and amending a patent application. Amending a patent that has issued is relatively uncommon because the United States Patent and Trademark Office (PTO) has already exhaustively examined the application. This is very different from amending a patent application, which happens routinely during the course of patent prosecution.
  
  

Different Approaches

• According to section 1400.01 of the Manual of Patent Examining Procedures (MPEP), "a patent may be corrected or amended in four ways, namely: A) by reissue, B) by the issuance of a certificate of correction which becomes a part of the patent, C) by disclaimer, and D) by reexamination." Each of these has very different implications as to the validity of the patent and the owner's interest in the patent.
  
  

Reissue

• According to section 1401.00 of the MPEP, a patent can be amended by reissue if "an error made without deceptive intent" and the error makes the patent "wholly or partly inoperative or invalid". Unless a typographical or editorial error changes the meaning of the text in an extraordinary way, such errors are not grounds for reissue because they do not render the patent in operative or invalid. Common reasons for reissue include inaccuracies in the disclosure, incorrect information about the foreign priority, incorrect reference to co-pending applications. The term of a patent is not changed through reissue because the term was established when the original patent granted.
  
  

Certificate of Correction

• A patent may also be amending through the issuance of a Certificate of Correction. According to 35 USC 254, the director of the PTO may issue a Certificate of Correction if the PTO has made a mistake in the printing of a patent. The Certificate will state "the fact and nature of such mistake" and "shall be attached to each printed copy of the patent." The certificate may be requested by the patentee or the patentee's assignee. Third parties may also supply information to the PTO regarding mistakes, but the PTO has no duty to respond to such third party requests. The Official Gazette of the PTO reports every time a Certificate of Correction is issued.
  
  

Disclaimer

• A patent can also be amended by a disclaimer made by the owner. The patentee may disclaim one or more patent claims, and dedicate them to the public for the rest of the term of the patent. In disclaiming these claims, the patentee is relinquishing his interest in them. The patentee is not changing the text of the claims or making any statement at to their validity. Often inventors will disclaim a patent as a matter of public interest. For example, in disclaiming patent claims pertaining to a particular drug, the patentee allows anyone to make the drug.
  
  

Reexamination

• The patent office can also reexamine a patent. The purpose of reexamining the patent is to raise questions as to its validity in light of prior art (other earlier inventions). If the claims of the reexamined patent are invalid in light of the prior art, the claims are invalidated. If all of the claims are invalidated, the patent is nullified entirely.
  
  Anyone can request reexamination by filing a request with the PTO, submitting the prior art they believe might have bearing on the claims, and paying a fee. In very rare instances, an inventor might request reexamination of his own patents before challenging others.
  
  Although patent reexamination is very rare, it is occasionally newsworthy. For example patent number 6,004,596 for a "crustless peanut butter and jelly sandwich." This patent was assigned to Smuckers who tried to use it to exclude others from making products similar to their "Uncrustables." This patent was reexamined and all the claims were rejected.