KEYTRUDA's Expanding Reach Just Bought Merck More Time Than the Street Thinks

KEYTRUDA loses US patent exclusivity in 2028. Every analyst model, every fund manager pitch, every sell-side initiation mentions it. At roughly $25 billion in annual revenue — accounting for approximately 45% of Merck's total sales — the patent cliff is, frankly, staggering in scale. The standard playbook says revenue could decline 60-70% within three years of loss of exclusivity as biosimilars enter the market.

But the standard playbook may be wrong on timing. KEYTRUDA's subcutaneous formulation, currently in late-stage trials, could extend effective exclusivity by 2-3 years beyond the 2028 date. Each new indication adds complexity for biosimilar developers, who need to demonstrate equivalence across a growing range of tumour types and combination regimens. Forty approved indications is not just a marketing achievement — it is a biosimilar deterrent.

The more interesting story is MK-0616, Merck's oral PCSK9 inhibitor. The existing PCSK9 drugs — Repatha and Praluent — are injectables that proved too inconvenient for mass adoption despite extraordinary LDL reduction. An oral version that delivers similar efficacy could tap into a cardiovascular market worth $20-30 billion annually.

Phase 3 data, released in late 2025, showed 50-55% LDL reduction — competitive with injectable PCSK9 inhibitors and meaningfully better than ezetimibe. The FDA decision is expected in Q3 2026. If approved, MK-0616 could reach $3-5 billion in peak sales, though the ramp would take until 2030-2031 to fully materialise.

The last time a major pharma company launched an oral alternative to an injectable blockbuster class was AbbVie with Rinvoq in the JAK inhibitor space. The commercial trajectory exceeded initial estimates by roughly 30% in the first two years. If MK-0616 follows a similar pattern, Merck's post-KEYTRUDA revenue gap narrows considerably.

Merck has spent $30 billion on acquisitions since 2022 — Prometheus Bio for the inflammatory bowel disease pipeline, Acceleron for cardiovascular, and a string of smaller oncology deals. The result is one of the deepest pipelines in large-cap pharma: 30+ programs in Phase 2 or later, spanning oncology, cardiovascular, immunology, and infectious disease.

By comparison, Pfizer's post-Seagen portfolio is still largely pre-commercial. AbbVie's Humira replacement cycle is well advanced but concentrated in immunology. Merck's diversification across therapeutic areas provides a broader set of options to offset the KEYTRUDA cliff — even if no single asset replaces the franchise on its own.