Merck's Japan Nod Sets Stage for Keytruda Patent Defense

Merck's Japan Nod Sets Stage for Keytruda Patent Defense Japan’s Ministry of Health, Labor and Welfare (MHLW) approved KEYTRUDA QLEX, a subcutaneous formulation of Merck’s blockbuster oncology drug, for all of the therapy's existing indications in the country. The new version combines pembrolizumab with berahyaluronidase alfa-pmph, allowing for a one-minute administration time. This stands in stark contrast to the 30- to 60-minute intravenous infusion required for the original formulation. ## Background Keytruda, an anti-PD-1 therapy, is Merck’s single most important product and a primary driver of its revenue. The market’s focus remains fixed on the drug's composition of matter patent, which expires later this decade. That event will open the door to biosimilars—near-identical copies of a biologic drug that are typically sold at a significant discount, threatening the originator’s market share and pricing power. The consensus has long been that Keytruda revenue will face a steep decline post-expiry, a risk priced into Merck's current valuation. This approval represents the first major test of Merck's life-cycle management strategy. Shifting patients from an intravenous (IV) to a subcutaneous (subQ) formulation is a well-established tactic to defend a franchise. The convenience of a one-minute injection, versus a lengthy infusion session, provides a compelling reason for doctors and patients to switch. By establishing the subQ version as the new standard of care before the IV patent expires, Merck aims to build a moat that biosimilars, which are being developed to mimic the original IV version, will struggle to cross. ## Why it matters While the approval is for the Japanese market, its significance is global. This is the first regulatory green light for subQ Keytruda, serving as a critical proof-of-concept for pending reviews in the larger, more lucrative U.S. and European markets. The move de-risks a core pillar of the long-term bull case for Merck: that it can successfully defend a substantial portion of the multi-billion dollar Keytruda revenue stream past the patent cliff. A successful global switch would reshape the terminal value calculation for the company’s largest asset. The approval places developers of Keytruda biosimilars in a difficult position. Their products are designed to compete with the IV formulation. If Merck can achieve a high rate of conversion to the subQ version, the addressable market for IV biosimilars will shrink considerably, damaging their commercial prospects. The move also applies pressure on competitors in the PD-1/L1 inhibitor class, such as Bristol Myers Squibb's Opdivo, by reinforcing Keytruda's market-leading position with a significant convenience advantage. ## What to watch The focus now shifts to execution and expansion. Investors will parse management’s commentary on the next earnings call for details on the launch, uptake, and pricing strategy for the newly approved product in Japan, which will be marketed as KEYJECT. The most critical data points, however, will be updated timelines for regulatory filings and potential approval dates in the United States and the European Union. The market needs to see a clear and credible path to a global rollout well ahead of the patent cliff to price in a successful defense of the franchise.