{"id":39506,"date":"2026-08-27T09:32:00","date_gmt":"2026-08-27T13:32:00","guid":{"rendered":"https:\/\/www.drugpatentwatch.com\/blog\/?p=39506"},"modified":"2026-08-21T14:45:55","modified_gmt":"2026-08-21T18:45:55","slug":"the-patent-cliff-is-a-myth-what-actually-happens-is-a-patent-staircase-and-most-models-miss-the-steps","status":"publish","type":"post","link":"https:\/\/www.drugpatentwatch.com\/blog\/the-patent-cliff-is-a-myth-what-actually-happens-is-a-patent-staircase-and-most-models-miss-the-steps\/","title":{"rendered":"The Patent Cliff Is a Myth. What Actually Happens Is a Patent Staircase, and Most Models Miss the Steps"},"content":{"rendered":"\n
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In March 2022, the first generic version of Bristol Myers Squibb’s cancer drug Revlimid reached U.S. pharmacies. It launched at 86.4% of the branded price, a discount of just 13.6%.[1]<\/sup> That is not what a patent cliff looks like. A patent cliff describes one date, after which a branded drug’s revenue falls off a ledge. Revlimid did not fall off a ledge in 2022. It stepped down a staircase that started in 2019 and does not finish until 2026, with a separate step for every settlement, every country, and every volume cap negotiated along the way.[2]<\/sup><\/p>\n\n\n\n

The same pattern governs Humira, Eliquis, and Keytruda, three of the best-selling drugs in pharmaceutical history. Each has a composition of matter patent that expired or will expire years before generic or biosimilar competition actually arrives at full strength. Each has a documented, dated sequence of secondary patents, settlements, and regulatory exclusivities that determine the real competitive timeline. Most patent cliff models track one date: the compound patent. This article tracks the staircase, drug by drug, step by step, using primary sources: SEC filings, FDA and USPTO records, court decisions, and company settlement announcements.<\/p>\n\n\n\n

The Short Answer: What a Patent Staircase Is<\/strong><\/h2>\n\n\n\n

A patent staircase is the documented sequence of separate expiration, settlement, and exclusivity dates that together determine when a branded drug faces full generic or biosimilar competition, as opposed to the single composition of matter patent date that most cliff forecasts use. Four mechanisms build the steps: patent term extension, secondary and formulation patents, negotiated settlement dates that do not match any patent’s actual expiration, and FDA regulatory exclusivities that run independently of patent status. A drug can clear its primary patent and still face years of restricted, partial, or zero competition because of the steps still ahead of it.<\/p>\n\n\n\n

An Original Taxonomy: Four Types of Patent Staircase<\/strong><\/h3>\n\n\n\n

Reviewing the documented histories of Revlimid, Humira, Eliquis, and Keytruda shows four distinct staircase types. This taxonomy is original to this analysis, built from the case evidence below, not an established industry classification.<\/p>\n\n\n\n

Type 1: The Volume-Capped Settlement Ramp<\/strong><\/h4>\n\n\n\n

A brand settles patent litigation by granting each generic challenger a license to sell a capped, gradually increasing percentage of market volume, years before any patent actually expires and years before the license becomes unrestricted. Revlimid is the clearest documented example.<\/p>\n\n\n\n

Type 2: The Biosimilar Settlement Cascade<\/strong><\/h4>\n\n\n\n

A brand settles with each biosimilar challenger separately, but ties every settlement to the same calendar entry date or a narrow cluster of dates, so that a wave of products enters together long after the reference product’s core patent expired. Humira is the clearest documented example.<\/p>\n\n\n\n

Type 3: The Multi-Patent Litigated Tier<\/strong><\/h4>\n\n\n\n

Multiple Orange Book-listed patents on the same drug carry different expiration years. Litigation and settlement outcomes split generic challengers into groups, some entering on a negotiated date, others blocked until a later, separately litigated patent expires. Eliquis is the clearest documented example.<\/p>\n\n\n\n

Type 4: The Defensive Reformulation Pivot<\/strong><\/h4>\n\n\n\n

A brand builds a new formulation, device, or delivery method ahead of its core patent’s expiration, intending to shift patients to a newly patentable product before generic or biosimilar competition arrives for the original. The pivot itself can generate fresh litigation, adding a new, unplanned step. Keytruda’s subcutaneous formulation is the clearest documented example in progress.<\/p>\n\n\n\n

Why Patent Cliff Forecasts Miss the Steps<\/strong><\/h2>\n\n\n\n

Standard patent cliff coverage tracks the expiration of a drug’s primary composition of matter patent, then assumes generic or biosimilar entry follows soon after. That assumption fails for every high-revenue drug examined here.<\/p>\n\n\n\n

The Single-Date Fallacy in Loss-of-Exclusivity Forecasting<\/strong><\/h3>\n\n\n\n

Humira’s active ingredient patent expired in December 2016.[3]<\/sup> The first U.S. biosimilar did not launch until January 31, 2023, a gap of more than six years explained entirely by non-composition patents and settlement dates, not by the compound patent itself.[3]<\/sup> A forecast keyed only to the 2016 date would have been wrong by 74 months.<\/p>\n\n\n\n

What Cliff Models Actually Track, and What They Leave Out<\/strong><\/h3>\n\n\n\n

Most public loss-of-exclusivity databases start from Orange Book or Purple Book listings tied to the reference product’s primary patents. They do not always capture confidential settlement terms, volume caps, or parallel litigation against formulation patents that were not part of the original suit. Patent and exclusivity trackers such as DrugPatentWatch aggregate Orange Book, Purple Book, and litigation-derived data specifically to close that gap, since the settlement date, not the printed patent date, is usually the one that matters commercially.<\/p>\n\n\n\n

The Five Findings That Matter<\/strong><\/h2>\n\n\n\n
    \n
  1. Revlimid’s generic volume was capped at a mid-single-digit percentage of the market from March 2022, rising to no more than one-third by March 2025, with restrictions ending entirely on January 31, 2026, nearly seven years after the drug’s primary patent expired in 2019.[4][2]<\/sup><\/li>\n\n\n\n
  2. AbbVie filed 247 U.S. patent applications on Humira and was granted roughly 132 of them, with some claims running to 2034, even though the compound patent expired in 2016.[5][3]<\/sup><\/li>\n\n\n\n
  3. Eliquis carries three Orange Book patents with three different original expiration years, 2019, 2026, and 2031; a patent term extension pushed the middle date from February 2023 to November 2026, and settled generic makers now have an April 1, 2028 entry date that matches none of the three original patent years.[6][7]<\/sup><\/li>\n\n\n\n
  4. Merck is building a subcutaneous Keytruda ahead of the drug’s roughly 2028 core patent expiration, and that defensive move has already triggered a new, separate lawsuit from Halozyme Therapeutics over 15 formulation-delivery patents, filed April 24, 2025.[8]<\/sup><\/li>\n\n\n\n
  5. Patent term extension under 35 U.S.C. \u00a7 156 is capped at five added years and at fourteen total years of exclusivity measured from FDA approval, meaning it can never by itself explain a staircase step longer than five years.[9][10]<\/sup><\/li>\n<\/ol>\n\n\n\n

    The Legal Machinery Behind Every Staircase Step<\/strong><\/h2>\n\n\n\n

    Every staircase step traces back to a specific statute, regulation, or negotiated agreement. Understanding the mechanics explains why the steps exist at all.<\/p>\n\n\n\n

    Composition of Matter Patents and the Twenty-Year Baseline<\/strong><\/h3>\n\n\n\n

    A utility patent runs 20 years from its filing date.[10]<\/sup> Because companies typically file years before FDA approval, the commercially useful remainder at launch averages roughly 10 to 12 years, not 20.[10]<\/sup><\/p>\n\n\n\n

    Patent Term Extension Under 35 U.S.C. \u00a7 156: The Five-Year, Fourteen-Year Math<\/strong><\/h3>\n\n\n\n

    Patent term extension restores time lost to FDA clinical testing and review. The statute caps the restoration at five years, and caps total exclusivity, patent term plus extension, at fourteen years from the date of FDA approval.[9]<\/sup> Eliquis used this mechanism to move its middle Orange Book patent from a February 2023 expiration to November 2026.[7]<\/sup><\/p>\n\n\n\n

    Pediatric Exclusivity: Six Months Under 21 U.S.C. \u00a7 355a<\/strong><\/h3>\n\n\n\n

    Completing an FDA-requested pediatric study adds six months to existing patent and regulatory exclusivities, whether or not the study itself succeeds.[11]<\/sup> Six months sounds small. On a multibillion-dollar drug, it is rarely small in dollar terms, which is why companies routinely pursue it even when they are skeptical of its clinical value.<\/p>\n\n\n\n

    BPCIA’s Twelve-Year Biologic Exclusivity Floor<\/strong><\/h3>\n\n\n\n

    The Biologics Price Competition and Innovation Act, enacted in 2010, blocks FDA approval of any biosimilar for twelve years from the reference biologic’s first approval, regardless of patent status.[11]<\/sup> For Humira, approved in 2002, that floor expired in 2014, long before the actual 2023 biosimilar launch date. The twelve years were never the binding constraint; the patent thicket built on top of them was.<\/p>\n\n\n\n

    Hatch-Waxman Paragraph IV Certification and the Settlement Layer<\/strong><\/h3>\n\n\n\n

    Under Hatch-Waxman, a generic applicant can certify that a listed patent is invalid or will not be infringed, triggering litigation and, typically, a negotiated settlement rather than a final court judgment. Revlimid, Humira, and Eliquis were all resolved this way, and in each case the settlement date, not a court’s patent-validity ruling, became the operative staircase step.[4][3][6]<\/sup><\/p>\n\n\n\n

    Why an Orange Book Listing Does Not Guarantee Enforceability<\/strong><\/h3>\n\n\n\n

    The FTC ran a multi-round campaign between November 2023 and May 2025 disputing more than 400 Orange Book patent listings it viewed as improperly claimed, on the theory that some listed patents cover devices or administrative features rather than the drug substance or an approved use.[12]<\/sup> A listed patent and an enforceable, litigation-tested patent are not the same step on the staircase, and treating them as identical overstates a brand’s real protection.<\/p>\n\n\n\n

    Case Study One: Revlimid’s Volume-Capped Staircase<\/strong><\/h2>\n\n\n\n

    Revlimid (lenalidomide), Bristol Myers Squibb’s multiple myeloma treatment, generated $12.8 billion in 2021 sales, its final full year without any generic competition.[2]<\/sup> Its case shows Type 1 staircase construction in more documented detail than any other blockbuster drug.<\/p>\n\n\n\n

    Timeline: From 2019 Composition Expiry to 2026 Uncapped Entry<\/strong><\/h3>\n\n\n\n

    Revlimid’s primary composition of matter patent expired in 2019.[13]<\/sup> Instead of facing open competition, Celgene, then Bristol Myers Squibb after its 2019 acquisition of Celgene, settled separately with Natco Pharma, Dr. Reddy’s, Sun Pharma, Cipla, Alvogen, Apotex, and Teva, among others, over multiple years starting in 2015.[4]<\/sup> Each settlement granted the same basic structure: a volume-limited license beginning around March 2022, and an unrestricted license beginning January 31, 2026.[4][2]<\/sup><\/p>\n\n\n\n

    The Volume Ramp, Mapped<\/strong><\/h4>\n\n\n\n

    According to the advocacy group I-MAK, generic manufacturers were limited to no more than 7% of total market volume when entry began in early 2022.[14]<\/sup> Company disclosures describe the volume limit rising gradually each 12-month period, reaching no more than one-third of total volume by March 2025, before all caps end on January 31, 2026.[4][2]<\/sup> Teva launched the first U.S. generic on March 7, 2022.[15]<\/sup> By the first quarter of 2026, after the caps lifted, BMS reported that Revlimid’s U.S. revenue had fallen 63% year over year.[16]<\/sup><\/p>\n\n\n\n

    \n

    “By the end, BMS will effectively have enjoyed 20 years of market exclusivity on Revlimid.”
    \u2014 I-MAK, April 2025[14]<\/sup><\/p>\n<\/blockquote>\n\n\n\n

    Milestone<\/th>Date<\/th>Source<\/th><\/tr>
    Primary composition of matter patent expires<\/td>2019<\/td>[13]<\/td><\/tr>
    Natco settlement: volume-limited entry begins<\/td>March 2022<\/td>[4]<\/td><\/tr>
    First U.S. generic launch (Teva)<\/td>March 7, 2022<\/td>[15]<\/td><\/tr>
    First-year volume cap<\/td>No more than ~7% of market<\/td>[14]<\/td><\/tr>
    Volume cap ceiling before removal<\/td>Up to one-third of market, by March 2025<\/td>[4][2]<\/td><\/tr>
    Last-to-expire Orange Book patent<\/td>April 2027<\/td>[4]<\/td><\/tr>
    All volume restrictions lifted<\/td>January 31, 2026<\/td>[4][2]<\/td><\/tr>
    U.S. revenue decline following uncapped entry (Q1 2026 vs. Q1 2025)<\/td>-63%<\/td>[16]<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    Notice that the unrestricted entry date, January 31, 2026, arrives before the last-to-expire Orange Book patent, listed as expiring in April 2027.[4]<\/sup> The settlement date, not the patent date, is the binding constraint. That gap is the staircase in miniature: a single drug, one court district, and still a negotiated date that has nothing to do with any single patent’s printed expiration.<\/p>\n\n\n\n

    Case Study Two: Humira’s Biosimilar Settlement Cascade<\/strong><\/h2>\n\n\n\n

    Humira (adalimumab), AbbVie’s anti-inflammatory biologic, is the best-selling drug in pharmaceutical history by cumulative revenue. Its patent estate is the most heavily documented example of a Type 2 staircase.<\/p>\n\n\n\n

    247 Filed, Roughly 132 Granted: The I-MAK Patent Count<\/strong><\/h3>\n\n\n\n

    According to I-MAK’s 2018 “Overpatented, Overpriced” report, AbbVie filed 247 U.S. patent applications covering Humira, of which roughly 132 were granted, some with terms extending to 2034.[5]<\/sup> Eighty-nine percent of those 247 applications were filed after Humira’s 2002 FDA approval, and nearly half were filed in 2014 or later, more than a decade after the drug reached the market.[17]<\/sup> The compound patent itself expired in December 2016; AbbVie has stated that non-composition patents extend no earlier than 2022.[3]<\/sup><\/p>\n\n\n\n

    The 2023 Launch Calendar: Amjevita’s Six-Month Head Start<\/strong><\/h3>\n\n\n\n

    Amgen settled its Humira patent litigation with AbbVie in September 2017, agreeing to delay its Amjevita biosimilar’s U.S. launch until January 31, 2023, in exchange for royalty payments and an earlier European launch date of October 16, 2018.[18]<\/sup> Seven additional AbbVie settlements followed the same template: delay U.S. entry to 2023, license the disputed patents, pay a royalty on launch.[19]<\/sup><\/p>\n\n\n\n

    Biosimilar<\/th>Manufacturer<\/th>FDA Approval<\/th>U.S. Launch Date<\/th><\/tr>
    Amjevita<\/td>Amgen<\/td>September 2016<\/td>January 31, 2023<\/td><\/tr>
    Cyltezo<\/td>Boehringer Ingelheim<\/td>August 2017<\/td>July 2023<\/td><\/tr>
    Hyrimoz<\/td>Sandoz\/Novartis<\/td>2018<\/td>July 2023<\/td><\/tr>
    Hadlima<\/td>Samsung Bioepis\/Organon<\/td>July 2019<\/td>July 2023<\/td><\/tr>
    Abrilada<\/td>Pfizer<\/td>2019<\/td>2023<\/td><\/tr>
    Yusimry<\/td>Coherus Biosciences<\/td>2021<\/td>July 2023<\/td><\/tr>
    Yuflyma<\/td>Celltrion<\/td>2023<\/td>July 2023<\/td><\/tr>
    Idacio<\/td>Fresenius Kabi<\/td>2022<\/td>July 2023<\/td><\/tr>
    Hulio<\/td>Biocon\/Mylan<\/td>2020<\/td>July 2023<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    Sources: [20][21][22]<\/em><\/p>\n\n\n\n

    Every one of those launch dates sits between six and seven years after the 2016 composition patent expiration, and the cluster in July 2023 shows how a settlement cascade produces a step function rather than a single cliff: one product enters alone for six months, then eight more arrive within weeks of each other.[21][20]<\/sup><\/p>\n\n\n\n

    Case Study Three: Eliquis’s Three-Patent, Two-Track Staircase<\/strong><\/h2>\n\n\n\n

    Eliquis (apixaban), the Bristol Myers Squibb and Pfizer anticoagulant, generated $14.4 billion in global sales in 2025.[23]<\/sup> Its Orange Book history is the clearest documented Type 3 example: three separately dated patents, and a settlement date that splits generic challengers into two distinct groups.<\/p>\n\n\n\n

    From Three Orange Book Dates to One Settlement Date<\/strong><\/h3>\n\n\n\n

    In 2017, twenty-five generic companies sent Paragraph IV certification letters challenging three Eliquis patents listed in the Orange Book, then set to expire in 2019, 2026, and 2031.[24]<\/sup> BMS and Pfizer sued every challenger.[24]<\/sup> A patent term extension later moved the 2026 composition of matter patent (U.S. 6,967,208) to November 2026.[7]<\/sup> In August 2020, a federal district court found both the composition patent and the 2031 formulation patent (U.S. 9,326,945) valid and infringed, a decision the Federal Circuit affirmed in September 2021.[25]<\/sup><\/p>\n\n\n\n

    The Settled-Versus-Litigated Fork: April 2028 Versus 2031<\/strong><\/h3>\n\n\n\n

    Generic manufacturers that settled with BMS and Pfizer received a licensed entry date of April 1, 2028.[25][6]<\/sup> Companies that continued litigating, including Sigmapharm, Sunshine Lake, and Unichem, lost their case and remain blocked from launching until the formulation patent’s 2031 expiration.[6]<\/sup> The same drug, the same reference patents, and two different generic entry years, four full years apart, depending only on which side of a settlement table a company sat on.<\/p>\n\n\n\n

    Patent \/ Event<\/th>Original \/ Current Date<\/th>Applies To<\/th><\/tr>
    First Orange Book patent<\/td>Expired 2019<\/td>All challengers<\/td><\/tr>
    Composition of matter patent (US 6,967,208), post-PTE<\/td>November 2026<\/td>All challengers<\/td><\/tr>
    Formulation patent (US 9,326,945)<\/td>2031<\/td>Litigating challengers still blocked<\/td><\/tr>
    Settled-generic entry date<\/td>April 1, 2028<\/td>Companies with settlements<\/td><\/tr>
    UK basic patent and SPC<\/td>Invalidated, October 2023<\/td>UK market only<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    Sources: [24][7][25][6][26]<\/em><\/p>\n\n\n\n

    A UK court invalidated the corresponding basic patent and supplementary protection certificate for apixaban, and the UK Supreme Court declined to hear BMS’s appeal in October 2023, illustrating that the same molecule can clear its staircase on an entirely different schedule outside the United States.[26]<\/sup><\/p>\n\n\n\n

    Case Study Four: Keytruda’s Defensive Reformulation Pivot<\/strong><\/h2>\n\n\n\n

    Keytruda (pembrolizumab), Merck’s PD-1 checkpoint inhibitor, is the world’s best-selling oncology drug, with quarterly sales of $7.2 billion as of early 2025.[27]<\/sup> Its core U.S. patent is approaching expiration around 2028.[27]<\/sup> Keytruda supplies the clearest active, still-unfolding Type 4 staircase among the four case studies.<\/p>\n\n\n\n

    Why Merck Is Building a Subcutaneous Keytruda Before 2028<\/strong><\/h3>\n\n\n\n

    Merck is developing a subcutaneous formulation of pembrolizumab, marketed as Keytruda Qlex, using a hyaluronidase enzyme licensed from Alteogen to allow rapid under-the-skin injection instead of a 30-minute intravenous infusion.[28][27]<\/sup> Merck’s own estimate is that 30% to 40% of patients could convert to the subcutaneous product within its first two years on the market, and that patients receiving single-agent or oral-combination regimens, roughly 50% of the total Keytruda population by 2028, are the most likely to switch.[28]<\/sup> A successful conversion would let Merck defend revenue on a newly patentable product even after the original intravenous compound patent lapses.<\/p>\n\n\n\n

    The Halozyme MDASE Fight as a Self-Inflicted New Staircase Step<\/strong><\/h3>\n\n\n\n

    On April 24, 2025, Halozyme Therapeutics sued Merck in the U.S. District Court for the District of New Jersey, alleging that subcutaneous Keytruda infringes 15 patents from Halozyme’s MDASE hyaluronidase portfolio.[29][30]<\/sup> Merck has denied infringement and filed post-grant review petitions at the USPTO challenging the validity of Halozyme’s patents.[29][31]<\/sup><\/p>\n\n\n\n

    PTAB Post-Grant Review Institutions, 2025 to 2026<\/strong><\/h4>\n\n\n\n

    Merck’s first post-grant review petition was instituted by the Patent Trial and Appeal Board in June 2025, and the board went on to institute 13 more of Merck’s petitions against the MDASE portfolio.[31]<\/sup> Merck filed inter partes review petitions against three remaining, unchallenged Halozyme patents in March 2026, with an institution decision expected by late September 2026.[31]<\/sup><\/p>\n\n\n\n

    The December 2025 German Injunction<\/strong><\/h4>\n\n\n\n

    Litigation is not confined to the United States. In December 2025, a German regional court granted Halozyme a preliminary injunction blocking Merck’s subcutaneous Keytruda in Germany, while leaving the intravenous version, which the injunction does not cover, available to patients.[30]<\/sup><\/p>\n\n\n\n

    Keytruda’s staircase, unlike Revlimid’s, Humira’s, or Eliquis’s, is not yet finished. It shows a fifth mechanism worth naming on its own: a brand’s defensive move to build a new step can generate a wholly new, unplanned legal fight before the original step is even reached.<\/p>\n\n\n\n

    Comparing the Four Staircases<\/strong><\/h2>\n\n\n\n
    Drug<\/th>Staircase Type<\/th>Core Patent Milestone<\/th>Actual Full-Competition Date<\/th>Gap<\/th><\/tr>
    Revlimid<\/td>Volume-Capped Settlement Ramp<\/td>2019 composition expiry<\/td>January 31, 2026<\/td>~7 years<\/td><\/tr>
    Humira<\/td>Biosimilar Settlement Cascade<\/td>December 2016 composition expiry<\/td>January 31, 2023 (first entrant); July 2023 (full cluster)<\/td>~6-6.5 years<\/td><\/tr>
    Eliquis<\/td>Multi-Patent Litigated Tier<\/td>November 2026 composition expiry (post-PTE)<\/td>April 1, 2028 (settled); 2031 (litigated)<\/td>~1.3 to 4.3 years<\/td><\/tr>
    Keytruda<\/td>Defensive Reformulation Pivot<\/td>~2028 core patent expiry<\/td>Undetermined; contested through at least 2026-2027 PTAB and court proceedings<\/td>Unresolved<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    Gap is calculated as an original analysis, measured from each drug’s core composition of matter milestone to its documented full-competition date. Sources: as cited in each case study above.<\/em><\/p>\n\n\n\n

    What This Means for Generic and Biosimilar Entry Timing<\/strong><\/h2>\n\n\n\n

    A generic or biosimilar developer cannot treat the composition patent date as the launch date. Revlimid’s example shows that even a successful patent challenge can produce a multi-year, volume-restricted entry rather than immediate full competition.[4]<\/sup> Humira shows that settling early, as Amgen did, can buy a real commercial advantage, a six-month solo launch window, over competitors who settle on the same eventual date but without that head start.[20]<\/sup> Eliquis shows that continuing to litigate after other companies settle carries real risk: three years of additional delay for the companies that fought Sigmapharm’s, Sunshine Lake’s, and Unichem’s case and lost.[6]<\/sup><\/p>\n\n\n\n

    What This Means for Brand Manufacturers<\/strong><\/h2>\n\n\n\n

    Brand manufacturers building their own staircase face a sequencing problem, not a single deadline. Merck’s Keytruda strategy shows the risk of the defensive-reformulation approach: building a new step can invite a new opponent, in this case Halozyme, with its own dense patent portfolio and its own willingness to litigate in multiple countries simultaneously.[29][30]<\/sup> AbbVie’s Humira strategy shows the opposite risk profile: heavy secondary filing bought years of delay, but at the cost of a widely cited public record, from I-MAK, congressional investigators, and the FTC, that is now shaping legislative proposals aimed specifically at reducing secondary-patent thickets.[17][32]<\/sup><\/p>\n\n\n\n

    Methodology: How This Staircase Analysis Was Built<\/strong><\/h2>\n\n\n\n

    Data Sources and Inclusion Criteria<\/strong><\/h3>\n\n\n\n

    This analysis draws on SEC filings (10-K, 10-Q, and 8-K disclosures from Bristol Myers Squibb, Pfizer, and Merck), company and law firm press releases announcing settlement terms, advocacy-group patent counts published by I-MAK with their underlying methodology disclosed, court decisions and Federal Circuit rulings, and contemporaneous trade press covering FDA approvals and biosimilar launch dates. A milestone was included in a case study timeline only where at least one primary source, a company filing, a court document, or a direct company statement, documented the specific date or figure. Where sources gave a range or an estimate rather than a confirmed date, that is noted in the text rather than presented as fixed.<\/p>\n\n\n\n

    Limitations<\/strong><\/h3>\n\n\n\n

    Several volume-cap percentages in the Revlimid settlements remain confidential by contract; this analysis uses the figures that have become public through litigation filings, company statements, and I-MAK’s independent compilation, and does not claim precision beyond what those sources disclose.[14][4]<\/sup> The Keytruda staircase is incomplete because the underlying litigation, PTAB proceedings, and the subcutaneous product’s ultimate market share are still unresolved as of this writing.[31]<\/sup><\/p>\n\n\n\n

    Patent Staircase vs. Patent Cliff vs. Patent Thicket: What Is the Difference?<\/strong><\/h2>\n\n\n\n

    These three terms describe related but distinct ideas, and conflating them produces bad forecasts.<\/p>\n\n\n\n

    Term<\/th>What It Describes<\/th>Example<\/th><\/tr>
    Patent cliff<\/td>The assumption that competition begins in full immediately after one patent’s expiration<\/td>Lipitor’s 2011 generic entry, close to a true cliff<\/td><\/tr>
    Patent thicket<\/td>A dense cluster of secondary patents filed to surround and extend protection of one product<\/td>Humira’s 247 filed applications<\/td><\/tr>
    Patent staircase<\/td>The documented, dated sequence of expiration, settlement, and exclusivity events that together determine actual competitive entry<\/td>Revlimid’s 2019-to-2026 volume-cap ramp<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    A thicket explains why a staircase has many steps. A staircase describes the dated sequence those steps actually form. A cliff is the (usually wrong) forecast that ignores both.<\/p>\n\n\n\n

    Scenario Analysis: What Happens If a Mid-Staircase Patent Falls Early?<\/strong><\/h2>\n\n\n\n

    Pfizer’s own 10-K disclosure lays out this scenario for Eliquis directly, rather than requiring outside estimation. If the 2031 formulation patent is held invalid or not infringed on appeal, the settled generic companies, and any generic company that wins its own case, would be permitted to launch on November 21, 2026, the date the composition patent expires, rather than waiting for April 1, 2028.[7]<\/sup> That is a documented, company-disclosed contingency, not a projection built by this analysis. It illustrates how a single mid-staircase ruling can collapse two remaining steps into one, moving a launch date forward by roughly 16 months.[7]<\/sup><\/p>\n\n\n\n

    Frequently Asked Questions<\/strong><\/h2>\n\n\n\n

    What is a pharmaceutical patent staircase?<\/strong><\/h3>\n\n\n\n

    It is the documented sequence of separate patent expirations, settlement dates, and regulatory exclusivities that together determine when a branded drug faces real generic or biosimilar competition, rather than the single date most patent-cliff coverage relies on.<\/p>\n\n\n\n

    Why did Revlimid’s generic entry take until 2026 to become unrestricted?<\/strong><\/h3>\n\n\n\n

    Celgene and Bristol Myers Squibb settled patent litigation with each generic challenger separately, granting volume-capped licenses starting around March 2022 that expanded gradually and did not become unrestricted until January 31, 2026, a date set by settlement rather than by any single patent’s expiration.[4][2]<\/sup><\/p>\n\n\n\n

    When will generic Eliquis be available in the United States?<\/strong><\/h3>\n\n\n\n

    Companies that settled with Bristol Myers Squibb and Pfizer are licensed to launch on April 1, 2028. Companies that continued litigating and lost, including Sigmapharm, Sunshine Lake, and Unichem, remain blocked until the formulation patent expires in 2031, unless a future appeal changes that outcome.[6][25]<\/sup><\/p>\n\n\n\n

    How many patents does AbbVie hold on Humira?<\/strong><\/h3>\n\n\n\n

    AbbVie filed 247 U.S. patent applications covering Humira, and approximately 132 were granted, according to I-MAK’s 2018 analysis, with some claims extending to 2034.[5]<\/sup><\/p>\n\n\n\n

    Why is Merck building a subcutaneous version of Keytruda before 2028?<\/strong><\/h3>\n\n\n\n

    Keytruda’s core intravenous patent is approaching expiration around 2028. Merck aims to convert a substantial share of patients, by its own estimate 30% to 40% within two years, to a newly patentable subcutaneous formulation before that date, to preserve revenue after generic biosimilar-style competition becomes possible for the IV product.[28][27]<\/sup><\/p>\n\n\n\n

    What is the difference between a patent cliff and a patent staircase?<\/strong><\/h3>\n\n\n\n

    A patent cliff assumes competition arrives all at once on a single date. A patent staircase describes the actual, documented sequence of dated steps, patent expirations, settlements, and regulatory exclusivities, that determine when competition arrives and how much of it arrives at each step.<\/p>\n\n\n\n

    How long can a biologic’s total exclusivity last once secondary patents are included?<\/strong><\/h3>\n\n\n\n

    The BPCIA’s 12-year reference exclusivity is a floor, not a ceiling. Humira’s 12-year BPCIA floor expired in 2014, yet secondary patents pushed the first U.S. biosimilar launch to January 2023, a total of roughly 21 years from approval.[11][3]<\/sup><\/p>\n\n\n\n

    What is patent term extension under 35 U.S.C. \u00a7 156, and how much time can it add?<\/strong><\/h3>\n\n\n\n

    It restores patent term lost to FDA clinical testing and regulatory review. The statute caps the addition at five years and caps total post-approval exclusivity at fourteen years.[9]<\/sup> Eliquis used this provision to move its composition patent expiration from February 2023 to November 2026.[7]<\/sup><\/p>\n\n\n\n

    Does an Orange Book listing guarantee that a patent is enforceable?<\/strong><\/h3>\n\n\n\n

    No. The FTC disputed more than 400 Orange Book listings between November 2023 and May 2025 on the theory that some listed patents, often covering delivery devices or administrative features, do not qualify for listing under the applicable regulations.[12]<\/sup> A listed patent and a litigation-tested, enforceable patent are different steps.<\/p>\n\n\n\n

    Can a generic company’s settlement date arrive before the underlying patent’s printed expiration date?<\/strong><\/h3>\n\n\n\n

    Yes. Revlimid’s settlements grant unrestricted generic entry on January 31, 2026, while the last-to-expire Orange Book patent is listed as expiring in April 2027.[4]<\/sup> The negotiated date, not the printed patent date, controls.<\/p>\n\n\n\n

    Key Takeaways<\/strong><\/h2>\n\n\n\n
      \n
    • Revlimid’s first U.S. generic launched at only a 13.6% discount to the branded price, and volume caps did not lift entirely until January 31, 2026, roughly seven years after the drug’s primary patent expired in 2019.[1][13][2]<\/sup><\/li>\n\n\n\n
    • AbbVie filed 247 patent applications on Humira and was granted about 132, with the first U.S. biosimilar launching more than six years after the compound patent expired.[5][3]<\/sup><\/li>\n\n\n\n
    • Eliquis carries three separately dated Orange Book patents, and its settled generic entry date of April 1, 2028 matches none of them; litigating generics remain blocked until 2031.[24][6]<\/sup><\/li>\n\n\n\n
    • Merck’s defensive subcutaneous Keytruda strategy has already generated a new, separate patent fight with Halozyme, filed in April 2025 and still active in U.S. and German courts.[29][30]<\/sup><\/li>\n\n\n\n
    • Patent term extension is capped by statute at five added years and fourteen total years from approval, which is why it alone never explains a multi-year staircase step.[9]<\/sup><\/li>\n\n\n\n
    • The BPCIA’s 12-year biologic exclusivity is a floor. For Humira, that floor expired nine years before the first biosimilar actually reached the market.[11][3]<\/sup><\/li>\n\n\n\n
    • The FTC disputed more than 400 Orange Book patent listings between late 2023 and mid-2025, a reminder that a listed patent is not automatically an enforceable one.[12]<\/sup><\/li>\n<\/ul>\n\n\n\n

      References<\/strong><\/h2>\n\n\n\n
        \n
      1. Global Pricing Innovations. (2026, June 23). Revlimid Patent Cliff: Essential 2026 Analysis<\/em>. https:\/\/globalpricing.com\/revlimid-patent-cliff-generic-competition\/<\/li>\n\n\n\n
      2. Bristol Myers Squibb Co. (2026, May). Form 10-Q, Q1 2026<\/em>. U.S. Securities and Exchange Commission. https:\/\/www.sec.gov\/Archives\/edgar\/data\/0000014272\/000001427226000010\/bmy-20260331.htm<\/li>\n\n\n\n
      3. GaBI Online. (n.d.). Amgen’s adalimumab biosimilar will only be launched in US in 2023<\/em>. Generics and Biosimilars Initiative. https:\/\/gabionline.net\/biosimilars\/news\/Amgen-s-adalimumab-biosimilar-will-only-be-launched-in-US-in-2023<\/li>\n\n\n\n
      4. Bristol Myers Squibb. (2020, September 17). Bristol Myers Squibb Announces Settlement of U.S. Patent Litigation for REVLIMID (lenalidomide) With Dr. Reddy’s<\/em>. https:\/\/news.bms.com\/news\/details\/2020\/Bristol-Myers-Squibb-Announces-Settlement-of-U.S.-Patent-Litigation-for-REVLIMID-lenalidomide-With-Dr.-Reddys\/default.aspx<\/li>\n\n\n\n
      5. IAM Media. (2019, January 31). Why evergreening is not a dirty word<\/em>. https:\/\/www.iam-media.com\/article\/why-evergreening-not-dirty-word<\/li>\n\n\n\n
      6. BioSpace. (2022, April 13). With Court Win, BMS and Pfizer Stave Off Eliquis Generic Challengers, For Now<\/em>. https:\/\/www.biospace.com\/with-court-win-bms-and-pfizer-stave-off-generic-challengers-to-eliquis-for-now<\/li>\n\n\n\n
      7. Pfizer Inc. (2026). Form 10-K, FY2025<\/em>. U.S. Securities and Exchange Commission. https:\/\/www.sec.gov\/Archives\/edgar\/data\/78003\/000007800326000026\/pfe-20251231.htm<\/li>\n\n\n\n
      8. FirstWord Pharma. (2025, March 5). Patent clash looms over Merck & Co.’s subcutaneous Keytruda<\/em>. https:\/\/firstwordpharma.com\/story\/5939918<\/li>\n\n\n\n
      9. Sterne Kessler. (2025, October 22). Patent Term Extension<\/em>. https:\/\/www.sternekessler.com\/news-insights\/insights\/patent-term-extension-2025\/<\/li>\n\n\n\n
      10. LegalClarity. (2026, May 21). How Long Do Drug Patents Last? 20 Years and Beyond<\/em>. https:\/\/legalclarity.org\/how-long-do-drug-patents-last-20-years-and-beyond\/<\/li>\n\n\n\n
      11. Initiative for Medicines, Access & Knowledge (I-MAK). (2024, May). Biologics, Biosimilars, and Patents<\/em>. https:\/\/www.i-mak.org\/wp-content\/uploads\/2024\/05\/Biologics-Biosimilars-Guide_IMAK.pdf<\/li>\n\n\n\n
      12. SEC EDGAR filing citing FTC Orange Book dispute campaign. (2024, April 2). Notice of Exempt Solicitation, AbbVie Inc.<\/em> https:\/\/investors.abbvie.com\/static-files\/ff34925a-5be8-4f35-807a-18da6c63d10e<\/li>\n\n\n\n
      13. Bristol Myers Squibb Co. (2022). Form 10-Q, Q1 2022<\/em>. U.S. Securities and Exchange Commission. https:\/\/www.sec.gov\/Archives\/edgar\/data\/14272\/000001427222000114\/bmy-20220331.htm<\/li>\n\n\n\n
      14. Initiative for Medicines, Access & Knowledge (I-MAK). (2025, April 4). How Celgene and Bristol Myers Squibb Used Volume Restrictions to Delay Revlimid Competition<\/em>. https:\/\/www.i-mak.org\/2025\/04\/04\/how-celgene-and-bristol-myers-squibb-used-volume-restrictions-to-delay-revlimid-competition\/<\/li>\n\n\n\n
      15. Fierce Pharma. (2022, March 7). Bristol Myers Squibb’s Revlimid finally faces competition in the U.S. with Teva’s generic launch<\/em>. https:\/\/www.fiercepharma.com\/pharma\/bristol-myers-squibbs-revlimid-finally-faces-competition-us-tevas-generic-launch<\/li>\n\n\n\n
      16. Bristol Myers Squibb Co. (2026). Form 10-Q, Q1 2026<\/em>, Legacy Portfolio disclosures. U.S. Securities and Exchange Commission. https:\/\/www.sec.gov\/Archives\/edgar\/data\/0000014272\/000001427226000010\/bmy-20260331.htm<\/li>\n\n\n\n
      17. Initiative for Medicines, Access & Knowledge (I-MAK). (2018, December 18). Report Finds 89% of Total U.S. Patent Applications on Humira Were Filed After FDA Approval<\/em>. https:\/\/www.i-mak.org\/2018\/12\/18\/report-finds-89-of-total-u-s-patent-applications-on-humira-were-filed-after-fda-approval-pointing-to-a-deliberate-strategy-to-delay-competition\/<\/li>\n\n\n\n
      18. GaBI Online. (2021, June 18). Market gears up for biosimilar boom in 2023 as Humira exclusivity draws to a close<\/em>. Healio Rheumatology. https:\/\/www.healio.com\/news\/rheumatology\/20210617\/market-gears-up-for-biosimilar-boom-in-2023-as-humira-exclusivity-draws-to-a-close<\/li>\n\n\n\n
      19. Pharmaceutical Technology. (2023, March 24). Comparison of Humira biosimilars in the US and Europe<\/em>. https:\/\/www.pharmaceutical-technology.com\/pricing-and-market-access\/comparison-humira-biosimilars\/<\/li>\n\n\n\n
      20. Amgen. (2023, January 31). AMJEVITA, First Biosimilar to HUMIRA, Now Available in the United States<\/em>. https:\/\/www.amgen.com\/newsroom\/press-releases\/2023\/01\/amjevita-adalimumabatto-first-biosimilar-to-humira-now-available-in-the-united-states<\/li>\n\n\n\n
      21. Big Molecule Watch. (2023, July 6). HUMIRA (adalimumab) Biosimilar Launches<\/em>. https:\/\/www.bigmoleculewatch.com\/2023\/07\/06\/humira-adalimumab-biosimilar-launches\/<\/li>\n\n\n\n
      22. AJMC. (2026, March 2). High-Concentration Version of Adalimumab Biosimilar Will Be Available in 2023<\/em>. https:\/\/www.ajmc.com\/view\/high-concentration-version-of-adalimumab-biosimilar-will-be-available-in-2023<\/li>\n\n\n\n
      23. Yahoo Finance \/ PharmaLive. (2026, May 26). Thinning revenues: inside the $14bn Eliquis patent cliff<\/em>. https:\/\/finance.yahoo.com\/sectors\/healthcare\/articles\/thinning-revenues-inside-14bn-eliquis-164234155.html<\/li>\n\n\n\n
      24. Pfizer Inc. (2019). Form 10-Q, Q1 2019<\/em>. U.S. Securities and Exchange Commission. https:\/\/www.sec.gov\/Archives\/edgar\/data\/78003\/000007800319000026\/pfe-03312019x10q.htm<\/li>\n\n\n\n
      25. Bristol Myers Squibb. (2021, September 3). The Bristol Myers Squibb-Pfizer Alliance is pleased with the decision by the U.S. Court of Appeals for the Federal Circuit upholding the Eliquis Patents<\/em>. https:\/\/news.bms.com\/news\/details\/2021\/The-Bristol-Myers-Squibb-Pfizer-Alliance-is-pleased-with-the-decision-by-the-U.S.-Court-of-Appeals-for-the-Federal-Circuit-upholding-the-Eliquis-Patents\/default.aspx<\/li>\n\n\n\n
      26. Pfizer Inc. (2025). Form 10-K, FY2024<\/em>, Note 16A1. U.S. Securities and Exchange Commission. https:\/\/www.sec.gov\/Archives\/edgar\/data\/78003\/000007800325000054\/pfe-20241231.htm<\/li>\n\n\n\n
      27. Fierce Pharma. (2025, March 6). In patent clash over injectable Keytruda, Merck and Halozyme dig in for a fight<\/em>. https:\/\/www.fiercepharma.com\/pharma\/patent-clash-over-injectable-keytruda-merck-and-halozyme-dig-fight<\/li>\n\n\n\n
      28. Fierce Pharma. (2025, April 24). Halozyme sues Merck over subcutaneous Keytruda as licensing talks fall through<\/em>. https:\/\/www.fiercepharma.com\/pharma\/halozyme-sues-merck-over-subcutaneous-keytruda-licensing-talks-fall-through<\/li>\n\n\n\n
      29. Lexology \/ Pearce IP. (2025, April 24). MSD\/Merck Sued for US Patent Infringement Over SC Pembrolizumab<\/em>. https:\/\/www.lexology.com\/library\/detail.aspx?g=0fcd1142-c835-4f5d-8316-acb612836be8<\/li>\n\n\n\n
      30. PR Newswire \/ Halozyme Therapeutics. (2025, December 4). Halozyme Wins Preliminary Injunction Against Merck’s Keytruda SC in Germany<\/em>. https:\/\/www.prnewswire.com\/news-releases\/halozyme-wins-preliminary-injunction-against-mercks-keytruda-sc-in-germany-302633457.html<\/li>\n\n\n\n
      31. Merck & Co., Inc. (2026). Form 10-Q, Q1 2026<\/em>. U.S. Securities and Exchange Commission. https:\/\/www.sec.gov\/Archives\/edgar\/data\/0000310158\/000162828026029802\/mrk-20260331.htm<\/li>\n\n\n\n
      32. Lown Institute. (2019, October 23). One drug, 247 patents, $18 billion<\/em>. https:\/\/lowninstitute.org\/one-drug-247-patents-18-billion\/<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"

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