⚠ Two More Patents, Both to Be LitigatedModerate threat

Merck & Co. (MRK) — threat to the moat

Two 2029 patents could buy Keytruda almost a year, and Merck's own filing assumes they will be litigated rather than respected.

Merck has two further American patents in the Keytruda composition-of-matter family, expiring in May and November 20291. If they held, biosimilars would arrive nearly a year later than the December 2028 date Merck gives.

Keytruda US sales ($M)15,114202317,872202418,8292025Merck Form 10-K FY2025, product sales note
The American pool the dates decide.

Merck does not count on them. It expects both patents to be the subject of litigation and therefore plans for biosimilar competition from December 20282. A company rarely publishes the pessimistic date; this one did.

The stakes are simple arithmetic. American Keytruda sales were $18,829 million in 20253. Each quarter of delay would be worth several billion dollars of sales at that rate.

History gives little comfort for secondary patents on biologics. Merck's general statement is that products losing exclusivity suffer a significant and rapid loss of sales4, and it has chosen to plan on the earlier date. If the company were confident in the 2029 patents, it would have no reason to publish December 2028.

The signal will be the first biosimilar filings and the lawsuits that follow them. If the courts leave the 2029 patents standing, Merck gains close to a year; if they fall early, December 2028 stands.

References
  1. ReportedMerck has two further American patents in the Keytruda composition-of-matter family, expiring in May and November 2029.
    Merck & Co. Form 10-K for fiscal 2025 - patents, exclusivity dates, biosimilar competition and royalties. — FY2025 · publ. 24 February 2026 · source ↗
  2. ReportedIt expects both patents to be the subject of litigation and therefore plans for biosimilar competition from December 2028.
    Merck & Co. Form 10-K for fiscal 2025 - patents, exclusivity dates, biosimilar competition and royalties. — FY2025 · publ. 24 February 2026 · source ↗
  3. ReportedAmerican Keytruda sales were $18,829 million in 2025.
    Merck & Co. Form 10-K for fiscal 2025 - Item 7 MD&A and product sales note: sales by product, segment and country. — FY2025 · publ. 24 February 2026 · source ↗
  4. ReportedMerck's general statement is that products losing exclusivity suffer a significant and rapid loss of sales, and it has chosen to plan on the earlier date.
    Merck & Co. Form 10-K for fiscal 2025 - patents, exclusivity dates, biosimilar competition and royalties. — FY2025 · publ. 24 February 2026 · source ↗
Sources
Generated September 25, 2026