In a recent memorandum opinion, Judge Sue L. Robinson granted a defendant’s motion for summary judgment of non-infringement under the doctrine of equivalents. Auxilium Pharmaceuticals, Inc. v. Upsher-Smith Laboratories, Inc., Civ. No. 13-148-SLR (D. Del. Dec. 4, 2013). The parties had stipulated previously that the defendant’s pharmaceutical formulation did not literally infringe the plaintiff’s patented methods for treating hypogonadism using a specific formulation of testosterone gel. The claims in the patents in suit focused on cyclic Hsieh enhancers, whereas the defendant’s formulation used Dudley enhancers, which the patentee gave up during prosecution. As the Court explained, “a large number of enhancers were known in the art, many of which the patentees referenced in their specification. The patentees specifically discussed the straight chain Dudley enhancers in the specification and, thereafter, differentiated the cyclic Hsieh enhancers.” Id. at 13. Further, the patentees “argued during prosecution that their invention was not obvious in light of Dudley enhancers . . . .” Id. The Court therefore found that the plaintiff could not recover through the doctrine of equivalents what it surrendered during prosecution. Id. at 13-14.