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Aaron Stiefel represents leading research-based pharmaceutical and biotechnology companies, such as Pfizer Inc. and Novartis, in all aspects of complex patent litigations. His experience includes bringing and defending patent infringement actions concerning antibiotics, antihypertensives, antifungal medications, treatments for erectile dysfunction, the cloning of alpha-interferon, testing of blood for hepatitis C infection, monoclonal antibodies, contact lenses, surgical devices, methods for producing transgenic mice, smartphone apps, and data storage products. Aaron frequently represents research-based companies in litigation against generic drug manufacturers under the Hatch-Waxman Act. He has counseled clients with respect to a host of patent law issues and has authored articles and lectured on patent law. He has also represented pharmaceutical companies regarding false advertising and unfair competition claims.

Aaron has also handled a vast array of commercial litigation matters, at both the trial and appellate levels, in state and federal courts and in arbitration. His litigation experience includes cases involving inter alia, breach of contract and breach of fiduciary duty claims, product liability claims, alleged violations of the securities laws, bankruptcy claims, and claims regarding real property taxes.

He has handled jury trials, bench trials, Markman hearings and arbitrations, and has argued before both federal and state appellate courts and trial courts. Aaron also spent time as trial counsel in the office of the New York City Corporation Counsel.


  • Counsel for Pfizer in a set of patent litigations involving Pfizer’s Xeljanz/Xeljanz XR (tofacitinib citrate) for the treatment of rheumatoid arthritis. Pfizer Inc. v. Micro Labs USA Inc. et al., 1:17-cv-00158-LPS (D. Del.) and related cases.
  • Counsel for Pfizer in a set of patent litigations involving Pfizer’s Bosulif (bosutinib) for the treatment of leukemia. Wyeth LLC et al. v Alembic Pharmaceuticals Ltd. et al., 1:16-cv-01305-RGA (D. Del.) and related cases.
  • Pfizerin a patent infringement case against Teva. Successfully preserved Pfizer's market exclusivity for its blockbuster drug Viagra®, defeating a challenge by Teva Pharmaceuticals USA Inc., which sought FDA approval to sell a generic version of the drug. The court rejected Teva's assertions that the patent is invalid as having been obvious and unenforceable under the doctrine of inequitable conduct. Pfizer Inc. et al. v. Teva Pharmaceuticals USA Inc. et al., 2:10-cv-128 (E.D. Va.).
  • Pfizer in a patent infringement case against Apotex, Lupin, Mylan, Teva and Watson, involving Pfizer's blockbuster drug Celebrex®. Pfizer Inc. v. Lupin Pharma et al., 2:13-cv-121 (E.D. Va.).
  • Pfizer in patent infringement cases against generic drug manufacturers Actavis, Apotex and Mylan, based on each defendant's filing of an ANDA seeking FDA approval for generic versions of Viagra®. Pfizer Inc. v. Actavis Inc. et al., 1:10-cv-08197-TPG, (S.D.N.Y.).
  • Cephalon in patent infringement litigation against ANDA-filer seeking FDA approval to market generic version of Cephalon's Treanda® injection product. Cephalon Inc. v. Fresenius Kabi USA LLC, 1:15-cv-oo536-LPS (D. Del.).
  • Acorda Therapeutics in a set of patent infringement cases against eight generic drug manufacturers involving Ampyra® (dalfampridine), an oral medication to improve walking in people with multiple sclerosis (MS). Acorda Therapeutics Inc. v. Actavis et al., 1:14-cv-00882-LPS (D. Del.).
  • Pfizer in defense of a patent infringement case brought by Apotex related to Pfizer's Accupril® product. Apotex v. Pfizer Inc., 0:12-cv-60704 (S.D. Fl.).


LMG Life Sciences Guide
"Life Sciences Star"—General Patent Litigation (2017–2022)
"Life Sciences Star"—Hatch-Waxman Patent Litigation (Branded) (2017–2022)
"Life Sciences Star"—Intellectual Property (2015–2016)
IAM Patent 1000
Litigation (New York) (2016–2023)
Managing Intellectual Property
"IP Star" (New York) (2017-2022)



  • J.D., Harvard Law School, 1981, cum laude
  • M.A., Chemistry, Yeshiva University, 1978
  • B.A., Yeshiva University, 1978


  • New York
  • New Jersey
  • U.S. Court of Appeals for the Second Circuit
  • U.S. Court of Appeals for the Third Circuit
  • U.S. Court of Appeals for the District of Columbia Circuit
  • U.S. District Court, Northern District of California
  • U.S. District Court, District of New Jersey
  • Supreme Court of the United States


  • Member, American Bar Association
  • Member, NY State Bar Association
  • Member, Federal Circuit Bar Association