Japan IP court upholds patent for breakthrough nail fungus treatment
By Toko Sekiguchi ( May 21, 2025, 07:41 GMT | Insight) -- Japan’s Intellectual Property High Court has confirmed the validity of a patent for a novel topical nail fungus treatment, coming on the heels of a decision by the Japan Patent Office to uphold the patent amid challenging scientific and legal issues.Japan’s Intellectual Property High Court has confirmed the validity of a patent for a novel topical nail fungus treatment, coming on the heels of a decision by the Japan Patent Office, or JPO, to uphold the patent amid challenging scientific and legal issues. The case involves two Japanese pharmaceutical companies. The plaintiff, leading generic maker Sawai Pharmaceuticals, challenged a patent held by Kaken Pharmaceutical on the grounds that it lacked an inventive step. Kaken’s patent protects a topical formulation designed specifically for onychomycosis or nail fungal infections — a condition that has long eluded effective treatment due to the thick, keratinized structure of human nails. Japan Patent No. 4414623 covers a unique triazole derivative known as KP-103, or its salt, that overcomes the notorious barrier of nail permeability. At the time of Kaken’s patent application, it was commonly understood that treating nail fungus with topical medication was generally ineffective because antifungal agents could not easily penetrate the thick, hard nail to reach the infected area. This made months-long oral medication the primary treatment choice. However, due to side effects such as liver damage, there was a strong demand for the development of effective topical treatments. Kaken, a mid-sized drugmaker, specializes in orthopedics and dermatology. Sawai brought an invalidation claim to the JPO, arguing that based on prior art for treating skin fungal infections, a skilled person could have easily modified existing formulations to cover nail fungus, thereby rendering the invention unworthy of patent protection. It contended that simple extrapolation from known formulations meant that KP-103 was not sufficiently innovative. The JPO dismissed Sawai’s claims, acknowledging that the nail’s significantly thicker structure posed distinct technical challenges that couldn’t be easily addressed by adapting existing skin treatments. Experimental data showed that KP-103 effectively penetrated nail tissue and reduced fungal counts. Given the unpredictability of achieving such results with a topical agent, the JPO determined that the invention involved a non-obvious, inventive step deserving of patent protection. Sawai appealed, but the IP High Court upheld the JPO’s decision in an April 23 ruling. The court reiterated that nail tissue, being composed of several layers of densely packed keratin, creates an extraordinary barrier to drug absorption. Citing experimental studies, the court agreed with the JPO’s analysis that KP-103’s low tendency to bind to keratin allowed it to maintain high antifungal activity after penetrating the nail. Comparative data showing KP-103’s significant effect on reducing in fungal load versus conventional agents underscored that the formulation achieved a technical result that was unexpected — a quality not predicted by prior art. Although Sawai argued that adapting known skin therapies to nail conditions was an obvious step, the IP court supported the JPO’s findings that the complex nature of nail drug delivery rendered such adaptations far from straightforward, and dismissed the case.Please email editors@mlex.com to contact the editorial staff regarding this story, or to submit the names of lawyers and advisers....
Prepare for tomorrow’s regulatory change, today
MLex identifies risk to business wherever it emerges, with specialist reporters across the globe providing exclusive news and deep-dive analysis on the proposals, probes, enforcement actions and rulings that matter to your organization and clients, now and in the longer term.
Know what others in the room don’t, with features including:
Daily newsletters for Antitrust, M&A, Trade, Data Privacy & Security, Technology, AI and more
Custom alerts on specific filters including geographies, industries, topics and companies to suit your practice needs
Predictive analysis from expert journalists across North America, the UK and Europe, Latin America and Asia-Pacific
Curated case files bringing together news, analysis and source documents in a single timeline