Many local patent rules allow a patent owner to amend its infringement contentions after the Court issues its Markman ruling. Indeed, patent owners sometimes assume that they will be allowed to freely amend their infringement contentions just as they can freely amend their complaint. However, because the local patent rules were designed, in part, to crystallize a party’s contentions early in the case, requested amendments to contentions are sometimes denied by the Courts even after a Markman ruling. In Thermapure v. Just Right Cleaning, Case No. 2:11-cv-431 (E.D. Was. Nov. 7, 2012), Judge Whaley ruled that his Markman ruling did not constitute “good cause” for the plaintiff to amend its infringement contentions. Plaintiff argued there was “good cause” to add two new infringement contentions based upon the Court’s Markman interpretation of the claim term “predetermined temperature” in a patent relating to sanitization by heat. In support, Plaintiff cited Local Patent Rule 124 which allows amendment of infringement contentions upon a showing of: (1) good cause and, (2) no prejudice to the non-moving party. Under the Local Patent Rule, good cause would include a claim construction by the Court different from that proposed by the party seeking amendment. Here, however, because the Court adopted Plaintiff’s own proposed claim construction, the Court did not believe there was sufficient “good cause” for the Plaintiff to amend its infringement contentions. In its reasoning, Judge Whaley noted that in contrast to the more liberal policy for amending pleadings, “the philosophy behind amending claim charts is decidedly conservative, and designed to prevent the ‘shifting sands’ approach to claim construction.”   LG Elecs. Inc. v. Q—Lity Computer Inc., 211 F.R.D. 360, 367 (N.D.Cal. 2002). The local patent rules were “designed to require parties to crystallize their theories of the case early in the litigation and to adhere to those theories once they have been disclosed.”  O2 Micro Int’l Ltd. v. Monolithic Power Sys., Inc., 467 F.3d 1355, 1366 n. 12 (Fed. Cir. 2006) Key Takeaway:  While a plaintiff often is allowed to amend its infringement contentions after a Markman ruling,  a court may not allow such an amendment if it is based upon the same Markman ruling that  plaintiff requested in the first place.