Don Mizerk

Don Mizerk — Patent Litigation Practice Summary

Don Mizerk is a Chicago-based intellectual property partner at Husch Blackwell LLP, where he has practiced since 2009 (serving as office managing partner since 2015); he was previously a partner at Winston & Strawn LLP (1997–2009) and began his legal career as a Sixth Circuit law clerk and as Chief Assistant State's Attorney in Cook County. His practice is anchored in Hatch-Waxman/ANDA pharmaceutical litigation, with firm biographies listing dozens of blockbuster-drug Paragraph IV matters (Wellbutrin XL, Adderall XR, Cymbalta, Eliquis, Restasis, Strattera, and others). He has also handled patent cases across aluminum alloys, silicon-on-insulator manufacturing, software, gaming devices, and ergonomic accessories, with trial and appellate work before the Federal Circuit.

Side preference. Mizerk is consistently defendant-side, representing generic and specialty pharmaceutical manufacturers against innovator plaintiffs — consistent with his single tracked appearance (defense counsel in Merck v. Apotex Inc. et al.). Patexia has individually ranked him among the most active ANDA attorneys on the defendant side, and Husch Blackwell's announcement when he joined noted his practice focused on representing makers of generic pharmaceuticals. His clients include TWi Pharmaceuticals, Amerigen, Handa Oncology, Nanjing Noratech, and Sigmapharm.

Notable cases. His best-publicized recent win came in Merck Serono S.A. v. TWi Pharmaceuticals, Inc., where he helped invalidate all challenged claims of patents covering the MS drug Mavenclad® (cladribine) in IPR proceedings, with the PTAB decisions affirmed by the Federal Circuit in October 2025 (rehearing denied). Earlier results include a post-trial judgment of invalidity for TWi against Alkermes/Par over Megace ES (Par, Alkermes v. TWi, 2014 WL 694976 (D. Md.)) and a noninfringement judgment with an attorneys'-fee award in the Amrix/cyclobenzaprine MDL (D. Del. 2012). He also led trial defenses for Sigmapharm against Takeda's Trintellix suit (2021) and for Handa Oncology against Bristol-Myers Squibb's Sprycel patent claims.

PTAB/IPR. Mizerk is primarily a district-court/ANDA litigator rather than a career PTAB practitioner; his pro hac vice declaration in IPR2023-00049/-00050 (filed February 2024) states he had not previously appeared in an IPR. That said, the Mavenclad IPRs — which he helped try alongside Philip Segrest and Stephen Howe — were a notable PTAB success affirmed on appeal. Bar/education: J.D., Vanderbilt University Law School (Order of the Coif); B.A., Illinois Wesleyan University; admitted in Illinois (1988) and California (2000), before the Federal Circuit and U.S. Supreme Court.