{"id":23542,"date":"2024-06-17T14:44:50","date_gmt":"2024-06-17T18:44:50","guid":{"rendered":"https:\/\/www.drugpatentwatch.com\/blog\/?p=23542"},"modified":"2026-04-24T22:10:29","modified_gmt":"2026-04-25T02:10:29","slug":"divisional-patent-minefields-navigating-big-pharmas-patent-extension-strategies","status":"publish","type":"post","link":"https:\/\/www.drugpatentwatch.com\/blog\/divisional-patent-minefields-navigating-big-pharmas-patent-extension-strategies\/","title":{"rendered":"Divisional Patent Minefields: How Big Pharma Builds Legal Fortresses Around Blockbuster Drugs"},"content":{"rendered":"\n
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Patent cliffs get all the attention. Divisional patents do the real work.<\/p>\n\n\n\n

When a blockbuster drug faces loss of exclusivity, the compound patent expiring is rarely the whole story. The actual expiration timeline is determined by a layered stack of divisional patents, continuation-in-part filings, pediatric exclusivity add-ons, and Orange Book listings that most analysts never fully map. That gap between what the market expects and what the IP portfolio actually contains is where billions of dollars in revenue risk lives, and where the most consequential competitive intelligence decisions get made.<\/p>\n\n\n\n

This guide is for IP teams assessing portfolio durability, portfolio managers pricing LOE risk into equity models, generic manufacturers planning ANDA filing timelines, and R&D leads deciding where to invest in next-generation formulations. It covers the mechanics of divisional patent strategy, the specific IP architecture deployed by AbbVie, Novartis, and others, the legal vulnerabilities generics exploit, and the regulatory headwinds that are beginning to reshape the playbook.<\/p>\n\n\n\n

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What a Divisional Patent Actually Is, and Why the Definition Matters<\/strong><\/h2>\n\n\n\n

The Statutory Mechanics<\/strong><\/h3>\n\n\n\n

A divisional patent application, governed in the United States by 35 U.S.C. \u00a7 121, arises when a parent application contains claims directed to two or more distinct and independent inventions. The USPTO’s restriction requirement practice forces the applicant to elect one invention for prosecution in the parent; the non-elected inventions can then be pursued in divisional applications. Each divisional inherits the parent’s effective filing date, which is critical for prior art purposes, but it is examined independently and receives its own grant date and, therefore, its own 20-year term running from the filing date of the parent.<\/p>\n\n\n\n

That date inheritance is the core mechanism pharma companies exploit. A divisional filed the same day as a parent application but granted five years later effectively extends protection into what would otherwise be open territory. When paired with patent term adjustment (PTA) under 35 U.S.C. \u00a7 154(b), which compensates for USPTO examination delays, and patent term extension (PTE) under 35 U.S.C. \u00a7 156 for regulatory review periods, a single divisional can protect a product years past the point when casual observers assume exclusivity has ended.<\/p>\n\n\n\n

In Europe, the legal framework under Article 76 of the European Patent Convention (EPC) is broadly analogous: a divisional must be filed while the parent is pending, it cannot extend beyond the parent’s disclosure, and it inherits the parent’s filing date. The critical operational difference is that the EPO has introduced a two-level fee structure specifically designed to discourage cascading divisional chains, with fees escalating for each successive generation of divisional filed from the same parent. This policy does not exist at the USPTO, which is one reason American patent thickets tend to be denser than European ones for the same drug.<\/p>\n\n\n\n

Divisionals vs. Continuations vs. Continuations-in-Part<\/strong><\/h3>\n\n\n\n

These three prosecution tools are frequently conflated, and the conflation causes analytical errors when mapping a drug’s patent estate.<\/p>\n\n\n\n

A continuation application pursues additional claims on the same disclosed invention as the parent, using the same specification. No new matter is permitted. A continuation-in-part (CIP) adds new matter to the specification, which means claims supported only by the new matter get a new effective filing date, creating a hybrid document where different claim sets have different priority dates.<\/p>\n\n\n\n

A divisional is distinct because it is triggered by a restriction requirement: the inventions being split are supposed to be independent and distinct. In practice, the line between what constitutes a ‘distinct’ invention for divisional purposes and what constitutes an additional claim on the same invention for continuation purposes is contested regularly. Generic challengers frequently argue in Paragraph IV proceedings that patents listed in the Orange Book were improperly obtained through divisional practice that produced claims not genuinely distinct from the parent, or that the divisional claims are obvious over the parent’s disclosure.<\/p>\n\n\n\n

The Orange Book as a Disclosure Instrument<\/strong><\/h3>\n\n\n\n

Under the Hatch-Waxman Act, a New Drug Application (NDA) holder is required to list in the Orange Book every patent that claims the drug or a method of using the drug for which a claim of patent infringement could reasonably be asserted against an ANDA filer. Divisional patents that meet these criteria must be listed. Each new Orange Book listing resets the litigation clock: an ANDA filer that challenges the listed patent via a Paragraph IV certification triggers a 30-month stay of FDA approval (absent court action). A brand company with five Orange Book-listed divisionals can, in theory, obtain five consecutive 30-month stays against any single ANDA challenger, though federal courts have grown increasingly hostile to what they characterize as abusive use of the listing mechanism.<\/p>\n\n\n\n

The FDA’s 2021 final rule on Orange Book patent listing tightened the criteria for method-of-use listings and device-component listings, but compound patents and formulation patents obtained via divisional practice remain squarely within the listing requirements. IP teams should audit every listed patent against the current regulatory text to identify which listings are legally vulnerable.<\/p>\n\n\n\n

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Key Takeaways: Divisional Patent Fundamentals<\/strong><\/h2>\n\n\n\n

The effective filing date inheritance mechanism is the single most important feature of divisional practice for purposes of exclusivity extension. Divisionals, continuations, and CIPs each create distinct legal risk profiles for generic challengers and must be mapped separately when assessing a drug’s patent estate. Orange Book listings create automatic 30-month stays that can be triggered serially by multiple divisional listings, making the number of listed patents as commercially relevant as their individual strength.<\/p>\n\n\n\n

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Big Pharma’s Divisional Patent Playbook: Four Core Strategies<\/strong><\/h2>\n\n\n\n

Strategy 1: The Patent Thicket<\/strong><\/h3>\n\n\n\n

A patent thicket, in the pharmaceutical context, is a collection of overlapping patent rights that a generic manufacturer must either design around or successfully challenge before entering the market. Divisional patents are the primary construction material.<\/p>\n\n\n\n

The thicket strategy is most effective when each divisional covers a genuinely distinct aspect of the product that cannot easily be designed around. A formulation patent covering a specific polymer matrix used in an extended-release tablet is harder to design around than a method-of-use patent covering an indication where off-label prescribing is common. IP teams assessing the durability of a competitor’s thicket should classify each patent by its design-around feasibility, not merely its listed expiration date.<\/p>\n\n\n\n

The canonical thicket framework covers the compound itself (the base patent, typically expiring soonest), specific polymorphic or salt forms, formulation parameters such as particle size, release profile, or excipient ratios, manufacturing process claims, dosing regimen claims, and combination product claims where the drug is co-formulated or co-administered with a second agent. A thorough divisional filing program touches all of these layers. The compound patent may expire in 2026; the formulation divisional may not expire until 2031; the manufacturing process divisional may extend to 2034 if it was filed years after the original compound application.<\/p>\n\n\n\n

Strategy 2: Evergreening Through Indication Expansion<\/strong><\/h3>\n\n\n\n

Evergreening, in the strict technical sense, refers to the practice of obtaining secondary patents on modifications or new uses of an existing drug to extend commercial exclusivity past compound patent expiry. Divisional patents are one vehicle; new clinical development programs generating new NDA supplements or new NDAs are another.<\/p>\n\n\n\n

The most straightforward evergreening via divisionals involves method-of-use patents. If a compound’s original patent covers Treatment of Disease X, divisionals can be filed covering Treatment of Disease Y, co-administration with Agent Z, or use in a specific patient population defined by a biomarker. Each divisional method-of-use patent, if successfully listed in the Orange Book, forces any ANDA challenger to certify against it separately, adding litigation cost and delay.<\/p>\n\n\n\n

The regulatory complexity here is material. Under Hatch-Waxman, an ANDA need not seek approval for every approved indication, and a generic manufacturer can file a ‘carve-out’ label that omits a patented method of use. The brand company’s ability to maintain exclusivity on carved-out indications depends on whether that indication drives substantial prescription volume. For drugs where the patented indication constitutes 70% of scripts, the carve-out strategy is commercially devastating to the generic even without an injunction.<\/p>\n\n\n\n

Strategy 3: Lifecycle-Synchronized Divisional Filing<\/strong><\/h3>\n\n\n\n

Sophisticated IP teams do not file all divisionals from a parent application at once. They synchronize filings with the product’s commercial lifecycle to maximize the coverage window.<\/p>\n\n\n\n

Early in a drug’s commercial life, the priority is protecting the core compound and the lead indication. As the drug matures, the IP team monitors clinical development data, competitor formulation work, and prescriber behavior to identify which secondary patents will carry the most commercial weight. A divisional on a once-daily formulation filed when the drug is mid-lifecycle, tied to a supplemental NDA for the new formulation, can generate a fresh 30-month stay trigger and shift prescribing patterns toward the reformulated product before generic competition arrives on the original formulation.<\/p>\n\n\n\n

This is not incidental. In the six to twelve months before a major compound patent expiry, brand manufacturers routinely attempt to convert their installed patient base to the next-generation formulation, often accompanied by patient assistance programs, copay cards, and formulary negotiations designed to entrench the new product. The divisional patents covering the new formulation are the legal infrastructure supporting this commercial transition.<\/p>\n\n\n\n

The USPTO time pressure matters here. A divisional must be filed while the parent application is still pending, meaning before the parent is granted or abandoned. In practice, most divisional filing programs are executed during the initial prosecution phase. Later-cycle divisionals typically come from continuation or CIP filings rather than true divisionals, though the commercial function is the same.<\/p>\n\n\n\n

Strategy 4: Defensive Filing Against IPR and Paragraph IV Attack<\/strong><\/h3>\n\n\n\n

Inter partes review petitions have made compound patents significantly more vulnerable than they were pre-America Invents Act. From 2012 through 2024, pharmaceutical patents challenged via IPR at the Patent Trial and Appeal Board (PTAB) were invalidated in whole or in part in approximately 60-70% of cases where institution was granted, though the pharmaceutical invalidation rate has historically been somewhat lower than the overall IPR invalidation rate due to the level of documented clinical development data supporting claim priority.<\/p>\n\n\n\n

Divisional patents offer a specific defensive function in this environment. When a compound patent is successfully challenged via IPR or Paragraph IV litigation, the formulation and method-of-use divisionals remain standing unless separately challenged. Each challenge is a separate proceeding, with separate filing fees, separate discovery, and separate PTAB or district court proceedings. A well-structured divisional portfolio forces generic challengers to mount parallel attacks across multiple fronts simultaneously, a resource constraint that meaningfully affects the litigation economics of smaller generic manufacturers.<\/p>\n\n\n\n

The Federal Circuit has also created uncertainty around the ‘obviousness-type double patenting’ (ODP) doctrine, which can be asserted against divisional patents that claim obvious variations of the parent. However, the filing of a terminal disclaimer, in which the patent owner agrees the divisional will expire no later than the parent, defeats an ODP rejection while preserving the divisional’s value as a separate litigation target. Terminal disclaimers do not automatically appear in Orange Book listings and require specific analytical attention during patent estate review.<\/p>\n\n\n\n

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Key Takeaways: Core Divisional Strategies<\/strong><\/h2>\n\n\n\n

Patent thicket construction requires systematic filing across compound, polymorph, formulation, process, dosing regimen, and combination claims, with design-around feasibility assessed for each layer. Evergreening via method-of-use divisionals depends critically on indication-volume concentration: a carve-out label defeats the strategy when the carved-out indication represents a small share of prescriptions. Lifecycle-synchronized divisional filing, tied to supplemental NDA activity and commercial conversion programs, is the mechanism by which brand companies generate revenue continuity across patent cliffs. Terminal disclaimers used to defeat ODP rejections do not forfeit the strategic value of divisional patents as independent litigation targets.<\/p>\n\n\n\n

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AbbVie and Humira: The Definitive Case Study in Divisional Patent Architecture<\/strong><\/h2>\n\n\n\n

The IP Estate: Structure and Valuation<\/strong><\/h3>\n\n\n\n

Humira (adalimumab) generated cumulative global revenues exceeding $200 billion before biosimilar entry, making its patent estate the most studied and most criticized in pharmaceutical history. The core compound patent, US 6,090,382, covering the adalimumab antibody, expired in December 2016. AbbVie did not depend on that patent for U.S. exclusivity. Instead, the company assembled a portfolio of over 130 patents in the United States alone, a substantial portion of which were divisional or continuation filings covering manufacturing processes, formulation parameters, dosing regimens, and methods of use for specific conditions including rheumatoid arthritis, psoriasis, Crohn’s disease, and ankylosing spondylitis.<\/p>\n\n\n\n

The IP value locked in the Humira portfolio is quantifiable in structural terms. AbbVie’s royalty-bearing license agreements with biosimilar manufacturers, executed between 2017 and 2023, required licensees to pay royalties in the low-to-mid single-digit percentage range on U.S. biosimilar net sales, reflecting the licensees’ assessment that challenging the full portfolio would be more expensive than paying the royalty. Those royalty streams, which began flowing when U.S. biosimilar entry was permitted in January 2023, represent a direct monetization of the divisional patent estate. The present value of those royalty streams at the time the licenses were signed was estimated in the range of $3-5 billion by several sell-side analysts, based on projected biosimilar penetration curves and net price assumptions.<\/p>\n\n\n\n

The formulation patents, covering the citrate-free, high-concentration formulation introduced as Humira CF beginning in 2017, are a textbook example of lifecycle-synchronized divisional filing tied to a commercial conversion program. AbbVie’s field force actively converted patients from the original citrate-containing formulation to Humira CF in the two years before biosimilar entry. Biosimilar manufacturers whose products referenced the original formulation faced the additional barrier of demonstrating interchangeability with the CF product, which most had not characterized in their biosimilar applications.<\/p>\n\n\n\n

Investment Strategy: AbbVie’s Post-LOE Revenue Model<\/strong><\/h3>\n\n\n\n

For analysts modeling AbbVie’s revenue post-Humira, the divisional estate created several observable dynamics worth embedding in financial models. The royalty income from Humira biosimilar licensees appears in AbbVie’s other revenue line and has been material, running at approximately $200-400 million annually in the 2023-2025 period based on company disclosures. The Humira CF formulation, even as a branded product competing with biosimilars, retained formulary positions at several major PBMs longer than consensus expected, partly because the CF formulation patents gave AbbVie legal leverage in formulary negotiations.<\/p>\n\n\n\n

The broader lesson for portfolio managers: when evaluating a pharma company facing an LOE event, the divisional patent count and structure is more predictive of post-cliff revenue durability than the compound patent expiry date alone. A company with a 40-patent Orange Book listing on a major asset faces a fundamentally different competitive dynamic than one with a 4-patent listing, even if both company’s primary patents expire in the same year.<\/p>\n\n\n\n

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Novartis and Gleevec: Polymorph Patents, the Supreme Court, and the Limits of Secondary Patents<\/strong><\/h2>\n\n\n\n

The Beta-Crystalline Form and Imatinib Mesylate<\/strong><\/h3>\n\n\n\n

Gleevec (imatinib mesylate) generated peak annual revenues of approximately $4.7 billion for Novartis before generic entry. The core imatinib compound was synthesized in 1992 and was covered by patents that expired in various jurisdictions between 2013 and 2015. Novartis’s secondary patent strategy rested heavily on patents covering the beta-crystalline form of imatinib mesylate, the specific polymorph used in commercial manufacture. This is the type of divisional-adjacent filing, technically a separate patent application rather than a formal divisional, that has generated some of the most significant patent jurisprudence affecting pharmaceutical IP strategy globally.<\/p>\n\n\n\n

In the U.S., generic manufacturers including Mylan, Apotex, Teva, and Sandoz challenged the formulation and polymorph patents via Paragraph IV proceedings. Novartis prevailed in some challenges and settled others, with the net effect that generic imatinib entry into the U.S. market occurred in February 2016, roughly six months ahead of what would have been possible absent patent settlements.<\/p>\n\n\n\n

The more consequential litigation occurred in India. The Indian Supreme Court’s 2013 ruling in Novartis AG v. Union of India rejected Novartis’s application for a patent on the beta-crystalline form of imatinib mesylate under Section 3(d) of the Indian Patents Act, which requires that a secondary patent demonstrate enhanced efficacy over the known substance. The court held that improved bioavailability, without demonstrated enhancement of therapeutic efficacy, does not meet the Section 3(d) standard. The ruling fundamentally limited evergreening via polymorph patents in India and influenced patent reform debates in Brazil, South Africa, and several ASEAN markets.<\/p>\n\n\n\n

IP Valuation Impact of the India Ruling<\/strong><\/h3>\n\n\n\n

For Novartis, the India ruling’s financial impact was direct: the generic imatinib market in India opened fully, eliminating Gleevec’s pricing power in a market where the branded drug had been priced at approximately $2,700 per month versus generic availability at under $200. The more consequential long-term impact was on Novartis’s patent filing strategy for subsequent oncology compounds, particularly the shift toward claiming therapeutic efficacy data directly in patent specifications rather than relying on bioavailability proxies.<\/p>\n\n\n\n

For analysts assessing the durability of polymorph or salt-form secondary patents in multinational pharma portfolios, the India ruling is a benchmark. Any secondary patent whose primary novelty claim rests on a physical form rather than a demonstrated therapeutic advantage carries elevated invalidity risk in middle-income markets where Section 3(d)-style provisions have been adopted or are under legislative consideration.<\/p>\n\n\n\n

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Key Takeaways: Case Studies in Divisional Patent Valuation<\/strong><\/h2>\n\n\n\n

AbbVie monetized the Humira divisional estate not only through delayed generic entry but through royalty-bearing biosimilar licenses whose net present value runs into the billions; that royalty income is analytically distinct from product revenue and must be modeled separately. Novartis’s Gleevec polymorph strategy succeeded in the U.S. through settlement-driven timelines but failed in India under Section 3(d), creating a jurisdiction-specific bifurcation in exclusivity value that analysts in global pharma equity frequently underweight. The number of Orange Book-listed patents, their claim type distribution, and the proportion subject to active litigation are more predictive of post-LOE revenue durability than a single compound expiry date.<\/p>\n\n\n\n

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Biologics and Biosimilars: How Divisional Strategy Applies to the Biologic Patent Estate<\/strong><\/h2>\n\n\n\n

The 12-Year Exclusivity Baseline and the Patent Stack<\/strong><\/h3>\n\n\n\n

Biologic drugs operate under a different exclusivity architecture than small molecules. Under the Biologics Price Competition and Innovation Act (BPCIA), a reference biologic product receives 12 years of data exclusivity from the date of first FDA licensure, independent of any patent position. No biosimilar or interchangeable biosimilar can receive FDA approval during that 12-year period, regardless of patent status. This creates a baseline that small-molecule Hatch-Waxman exclusivity does not provide, but it does not make the patent estate irrelevant.<\/p>\n\n\n\n

Once data exclusivity expires, the biologic patent estate, including divisionals covering manufacturing processes, formulation parameters, and specific protein variants, governs the actual timeline of biosimilar market entry. The BPCIA’s patent dance provisions require the biosimilar applicant to disclose its manufacturing process to the reference product sponsor in the ‘patent dance,’ triggering a defined exchange of patent lists that determines which patents will be litigated before FDA licensure and which are reserved for post-licensure litigation.<\/p>\n\n\n\n

Divisional patents covering upstream bioprocessing steps, cell culture media composition, purification chromatography sequences, and protein glycosylation profiles are particularly powerful in biologic patent estates because they are difficult for biosimilar manufacturers to design around without altering the product’s comparability profile. A biosimilar manufacturer that changes its purification process must re-demonstrate analytical comparability, which may require additional clinical bridging data and adds regulatory delay.<\/p>\n\n\n\n

Technology Roadmap: Biologic Patent Estate Construction<\/strong><\/h3>\n\n\n\n

A comprehensive biologic patent estate for a monoclonal antibody typically develops across four phases. The first phase, covering preclinical through Phase II, generates patents on the antibody sequence, binding epitope, and mechanism of action. These are the equivalent of compound patents in small-molecule terms and typically have the earliest expiry dates.<\/p>\n\n\n\n

The second phase, coinciding with Phase III and BLA submission, generates manufacturing process patents as the commercial production process is locked. These cover cell line characteristics, fed-batch fermentation parameters, purification train design, and formulation composition. Divisional applications are typically filed from the original process patent application to separate the fermentation claims from the downstream purification claims and the formulation claims into distinct patent families, each independently listable in the BPCIA’s patent exchange.<\/p>\n\n\n\n

The third phase, post-approval, generates dosing regimen and combination therapy patents as real-world evidence accumulates and label expansions are sought. These method-of-use divisionals are the most vulnerable to carve-out strategies but the easiest to obtain, since they require only clinical data and a Paragraph IV or biosimilar patent dance challenge to enforce.<\/p>\n\n\n\n

The fourth phase involves second-generation product patents: subcutaneous formulations of IV-administered biologics, co-formulations, autoinjector device patents, and biosimilar interchangeability data that, paradoxically, can form the basis of new interchangeable product patents filed by the reference product sponsor for a next-generation formulation.<\/p>\n\n\n\n

Interchangeability as a Patent Strategy Variable<\/strong><\/h3>\n\n\n\n

FDA interchangeability designation under the BPCIA requires a biosimilar to demonstrate that it can be substituted for the reference product without prescriber intervention and without reduced safety or efficacy. Only a subset of approved biosimilars have sought and obtained interchangeability designation. Reference product sponsors have begun filing patents on their original formulation’s specific analytical characteristics, with the strategic intent of making the reference product’s properties a de facto interchangeability standard that biosimilars must meet, then using those patents to challenge biosimilars that make interchangeability claims based on the reference product’s labeled formulation.<\/p>\n\n\n\n

This strategy is at the frontier of BPCIA litigation and has not been fully adjudicated by the Federal Circuit. IP teams at reference product sponsors and biosimilar developers should treat formulation patents relevant to interchangeability as high-priority litigation risk items regardless of their listed expiry dates.<\/p>\n\n\n\n

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Investment Strategy: Modeling Biologic Patent Estate Value<\/strong><\/h2>\n\n\n\n

For institutional investors and portfolio managers pricing biologic assets, the relevant analytical framework for the patent estate is not a single expiry date but a probability-weighted timeline of effective market exclusivity that accounts for four variables. The first is the data exclusivity floor, which is jurisdiction-specific: 12 years in the U.S., 10 years in Europe for standard biologics, with possible extension to 11 years if approved for a new indication in the first 8 years of the exclusivity period. The second is the patent dance outcome, specifically which patents get litigated pre-licensure versus post-licensure and the historical settlement rate for the relevant claim types. The third is the manufacturing process patent durability, assessed by the degree to which the commercial process is specifically and narrowly claimed in ways that biosimilar manufacturers cannot design around. The fourth is the interchangeability timeline: biosimilar products that achieve interchangeability designation erode branded market share at roughly 2-3x the rate of non-interchangeable biosimilars based on IMS data from the adalimumab and etanercept markets.<\/p>\n\n\n\n

A biologic with strong data exclusivity, a dense manufacturing process divisional portfolio, and no currently approved interchangeable biosimilar trades at a valuation premium that is quantifiable: historical transactions involving biologic assets with 8+ years of remaining effective exclusivity have been priced at NPV multiples roughly 30-50% above those of assets with 3-4 years of remaining exclusivity, based on deal data from 2018-2024.<\/p>\n\n\n\n

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The Legal Attack Surface: How Generics Challenge Divisional Patents<\/strong><\/h2>\n\n\n\n

Paragraph IV Certifications and the Challenge Economics<\/strong><\/h3>\n\n\n\n

When an ANDA applicant files a Paragraph IV certification against an Orange Book-listed divisional patent, it represents a legal conclusion that the patent is invalid, unenforceable, or will not be infringed by the generic product. If the NDA holder sues within 45 days, the FDA is automatically stayed from approving the ANDA for up to 30 months. If the NDA holder does not sue, the ANDA can be approved immediately on the Paragraph IV certification.<\/p>\n\n\n\n

The economics of Paragraph IV challenges against divisional patents differ from compound patent challenges in two important ways. First, the invalidity argument for a divisional often rests on the relatedness of its claims to the parent, specifically whether the divisional claims are obvious in light of the parent’s specification, which is prior art to the divisional. The more closely the divisional claims track the parent’s disclosure, the stronger the obviousness-type double patenting argument, even if a terminal disclaimer has been filed. Second, the Hatch-Waxman 180-day exclusivity available to the first ANDA filer to challenge a patent applies per-patent: a first filer who challenges multiple divisional patents holds exclusivity on each challenged patent independently, creating a scenario where a single generic manufacturer can hold blocking exclusivity across multiple divisional challenge proceedings simultaneously.<\/p>\n\n\n\n

Inter Partes Review: The PTAB Pathway<\/strong><\/h3>\n\n\n\n

IPR petitions have become the preferred pre-litigation invalidity vehicle for generic manufacturers and their counsel, partly because PTAB proceedings are faster and cheaper than district court litigation and partly because the claim construction standard at PTAB, though now aligned with district court after the 2018 SAS Institute decision, has historically been more hospitable to challengers.<\/p>\n\n\n\n

For divisional patents, IPR petitions most commonly assert anticipation or obviousness over the parent application’s published disclosure combined with secondary references. The parent application, once published, becomes prior art to any continuation or divisional filed after its publication date, which for applications published 18 months after filing means that divisionals filed in the later stages of parent prosecution face a narrower window of novel claim space.<\/p>\n\n\n\n

Frequency of successful IPR petitions against pharma divisionals has been tracked by several IP analytics providers, and the institution rate for petitions asserting prior art specifically from the parent patent family is materially higher than the baseline pharmaceutical IPR institution rate. IP teams should treat this as a quantitative risk factor: a divisional patent whose claims are closely mirrored in the parent application’s specification is statistically more likely to face a successful IPR challenge than one covering genuinely new technical territory.<\/p>\n\n\n\n

Inequitable Conduct and the Prosecution History<\/strong><\/h3>\n\n\n\n

Inequitable conduct claims, which assert that a patent is unenforceable because the applicant withheld material information from the USPTO during prosecution with specific intent to deceive, are less commonly asserted as standalone invalidity arguments since the Federal Circuit’s 2011 Therasense decision raised the evidentiary bar. However, in divisional patent prosecution, the prosecution history of the parent application is always relevant to the divisional’s validity, and inconsistencies between positions taken in the parent prosecution and claims pursued in the divisional can form the basis of file wrapper estoppel arguments that limit the divisional’s claim scope under the doctrine of equivalents.<\/p>\n\n\n\n

IP counsel managing divisional prosecution programs should maintain explicit coordination between parent and divisional prosecution teams, tracking positions taken in the parent that might limit divisional claim scope. This is frequently overlooked in high-volume divisional filing programs where prosecution responsibility is distributed across different counsel or different national practices.<\/p>\n\n\n\n

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Key Takeaways: Legal Challenge Mechanisms<\/strong><\/h2>\n\n\n\n

Paragraph IV certifications against multiple Orange Book-listed divisionals give the challenging generic manufacturer independent 180-day exclusivity on each successfully challenged patent, creating a portfolio challenge incentive that is strategically distinct from single-patent challenges. IPR petitions asserting prior art from the parent patent family have a materially higher institution rate than average, making prior-art-over-parent the most analytically predictable challenge type for divisional patents. File wrapper estoppel from parent prosecution positions can limit divisional claim scope under the doctrine of equivalents, a risk that divisional prosecution teams frequently fail to systematically track.<\/p>\n\n\n\n

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Regulatory Headwinds: FTC, IRA, and the Global Crackdown<\/strong><\/h2>\n\n\n\n

The FTC’s Aggressive Posture on Patent Thickets<\/strong><\/h3>\n\n\n\n

The Federal Trade Commission’s interest in pharmaceutical patent thickets predates the Biden administration but intensified materially from 2021 onward. The FTC’s January 2024 report on pharmaceutical patent thickets documented that from 2005 to 2015, the ten best-selling brand-name drugs accumulated an average of 38 patents each in the Orange Book, a number far higher than any reasonable characterization of the drugs’ technical novelty would support. The report specifically identified that the majority of patents on these drugs were secondary patents, including formulation, method-of-use, and process divisionals, rather than compound patents.<\/p>\n\n\n\n

The FTC has pursued two legal theories against what it characterizes as abusive patent listing. The first is that Orange Book listings of patents that do not meet the Hatch-Waxman listing criteria constitute unfair competition under Section 5 of the FTC Act. The commission brought its first Section 5 action targeting Orange Book listings against Abbvie in 2020, resulting in a settlement that removed several Humira patents from the Orange Book without any finding of liability but signaled the commission’s willingness to use this tool. The second theory targets pay-for-delay settlements, where brand manufacturers pay generic manufacturers to delay entry. These settlements, also known as reverse payments, were addressed by the Supreme Court in FTC v. Actavis (2013), which held that large reverse payments can violate antitrust law and must be assessed under a rule of reason standard.<\/p>\n\n\n\n

The regulatory risk created by FTC scrutiny is not symmetrical across the industry. Companies with fewer than 30 Orange Book-listed patents per drug, a clear technical nexus between listed patents and the approved product, and no history of reverse payment settlements face substantially lower FTC enforcement exposure than companies with sprawling thickets built from divisionals covering marginal formulation variations.<\/p>\n\n\n\n

The Inflation Reduction Act and Its Effect on the Exclusivity Calculus<\/strong><\/h3>\n\n\n\n

The Inflation Reduction Act’s drug pricing negotiation provisions, effective for the first drugs beginning in 2026, have altered the commercial value of patent extension strategies in a specific and underappreciated way. Under the IRA, small-molecule drugs become eligible for Medicare price negotiation nine years after initial approval; biologics become eligible thirteen years after initial approval. Critically, the negotiation eligibility is triggered by FDA approval date, not by patent expiry.<\/p>\n\n\n\n

This creates a decoupling of patent strategy from revenue optimization that did not exist before the IRA. A divisional patent that extends exclusivity from year 10 to year 14 for a small-molecule drug provides four years of post-negotiation-eligibility exclusivity, where the drug is subject to a government-set price. The commercial value of those additional four years of exclusivity is materially lower than the pre-IRA value of equivalent exclusivity, because the IRA-negotiated price will be significantly below the list price the brand would otherwise maintain against generic competition.<\/p>\n\n\n\n

For IP teams and portfolio managers, this means the NPV of patent exclusivity years past the IRA negotiation eligibility trigger is systematically lower than the NPV of years before that trigger. Divisional patent filing programs that prioritize the early years of exclusivity through formulation or dosage form protection carry more commercial value than those focused on extending exclusivity deep into the post-negotiation period.<\/p>\n\n\n\n

The Unified Patent Court and Europe’s Diverging Path<\/strong><\/h3>\n\n\n\n

The Unified Patent Court, operational since June 2023 across most EU member states, has created a new risk-and-opportunity calculus for pharma divisionals in Europe. A single UPC decision on a European patent’s validity has pan-European effect. For a brand company holding European divisionals on a major drug, a successful invalidity action at the UPC can strip protection across multiple member states simultaneously. This is categorically different from the pre-UPC environment, where a successful national invalidity action in Germany did not automatically affect the same patent’s status in France or Italy.<\/p>\n\n\n\n

The EPO’s escalating divisional filing fees have already reduced the density of European divisional portfolios relative to U.S. portfolios for the same drugs. The UPC’s centralized challenge mechanism is likely to further concentrate European divisional strategy on the highest-value claim sets, since each divisional now represents both a litigation asset and a concentrated litigation liability.<\/p>\n\n\n\n

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Investment Strategy: Regulatory Risk Quantification<\/strong><\/h2>\n\n\n\n

For analysts pricing pharma assets with large divisional patent estates, the FTC enforcement risk, IRA negotiation trigger, and UPC concentration risk each require explicit model variables. The FTC risk is most directly quantifiable by Orange Book listing count and the proportion of listed patents that are secondary patents with a technical nexus weaker than the compound patent. A company with 40+ Orange Book listings on a single drug, more than 60% of which are formulation or method-of-use divisionals, should carry a regulatory risk discount in IP valuation models that companies with tighter, more technically defensible portfolios do not. The IRA trigger discount can be modeled mechanically: identify the negotiation eligibility year for each asset and apply a haircut to projected revenues in subsequent years based on CBO scoring of average negotiated price discounts, which have run approximately 25-60% below average manufacturer price in initial negotiations. The UPC liability is the least quantifiable but most acute for European biologics with manufacturing process divisionals: centralized invalidity risk should be modeled as a binary scenario rather than a probability distribution, since UPC decisions have no partial effect.<\/p>\n\n\n\n

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Building the Counter-Strategy: Generic Manufacturer and Challenger Playbook<\/strong><\/h2>\n\n\n\n

Freedom-to-Operate Analysis as a Planning Instrument<\/strong><\/h3>\n\n\n\n

Freedom-to-operate (FTO) analysis for a drug subject to a divisional patent thicket requires a scope that goes well beyond the standard prior art search. The analysis must map every listed Orange Book patent and every patent in the same family (parents, siblings, divisionals, continuations, and CIPs), assess each claim for infringement by the proposed generic or biosimilar product, and identify which patents are most vulnerable to invalidity challenge based on their claim specificity and prosecution history.<\/p>\n\n\n\n

The FTO analysis should also identify the patent chain’s ‘weakest link,’ the divisional most likely to be invalidated at PTAB or in district court, and sequence the legal challenge strategy accordingly. In most thicket situations, challenging only the weakest link is insufficient: the remaining patents still provide grounds for a 30-month stay or a preliminary injunction. Effective challenge strategies typically involve parallel proceedings targeting two or three high-priority patents simultaneously, accepting the additional cost in exchange for the ability to neutralize stay-generating capacity across the thicket.<\/p>\n\n\n\n

Inter Partes Review Timing and the PTAB Serial Petition Problem<\/strong><\/h3>\n\n\n\n

A significant strategic complication for generic IPR petitioners is the PTAB’s discretionary authority to deny institution under 35 U.S.C. \u00a7 314(a), which the board has used to decline petitions that raise the same or substantially the same prior art and arguments as a previously filed petition against the same patent. This means a generic manufacturer that files a weak first IPR petition and loses institution has made it harder, not easier, to bring a stronger petition later. IPR strategy for divisional patent challenges requires getting the petition right the first time, which demands a thorough analysis of the patent’s prosecution history, the available prior art, and the specific claim elements that are most vulnerable.<\/p>\n\n\n\n

The timing of IPR petitions relative to district court litigation also requires attention. Under the one-year bar of 35 U.S.C. \u00a7 315(b), an IPR petition is barred if the petitioner was served with a complaint alleging infringement of the patent more than one year before the petition is filed. A generic manufacturer sued by the brand on a Paragraph IV certification must file any IPR petition within one year of service. Given the 30-month stay of ANDA approval, this one-year window typically falls well within the stay period, meaning IPR petitions can be pursued in parallel with district court litigation, but the timing requires coordination between district court and PTAB litigation teams.<\/p>\n\n\n\n

Declaratory Judgment as a Pre-Emptive Tool<\/strong><\/h3>\n\n\n\n

A generic manufacturer that has not yet been sued on a divisional patent can seek a declaratory judgment of invalidity or non-infringement in federal district court if it can establish an actual case or controversy. In the Hatch-Waxman context, the filing of a Paragraph IV certification itself creates an actual controversy, but declaratory judgment actions can also be brought by companies that are designing around a patent and have a reasonable apprehension of suit. For a generic manufacturer planning to design around a specific formulation divisional, filing a declaratory judgment action before the ANDA submission can lock in the venue and timeline for invalidity adjudication.<\/p>\n\n\n\n

\n\n\n\n

Practical Due Diligence: Patent Estate Assessment for M&A and Licensing<\/strong><\/h2>\n\n\n\n

What IP Teams Miss in Divisional Portfolio Review<\/strong><\/h3>\n\n\n\n

The most common analytical error in pharmaceutical patent estate review is treating the Orange Book listing as a complete inventory of the relevant IP. It is not. The Orange Book lists patents meeting specific criteria, but a company’s full divisional portfolio includes patents that are not Orange Book-listed because they cover manufacturing processes, upstream chemistry, or method-of-use claims for non-FDA-approved indications. These non-listed patents are enforceable against competitors who infringe them, and they represent both licensing opportunities and litigation risk that does not appear in standard patent expiry analysis.<\/p>\n\n\n\n

In M&A due diligence, the acquirer’s IP team should independently map the full patent family, including all divisionals, continuations, and CIPs, for each major asset. The patent family tree identifies prosecution histories, terminal disclaimers, and claim scope limitations that affect the defensible exclusivity period. A drug with a listed compound patent expiring in 2028 but manufacturing process divisionals expiring in 2032, none of which are Orange Book-listed, may have a defensible exclusivity period meaningfully longer than the Orange Book would suggest, provided the process divisionals cover steps that biosimilar or generic manufacturers cannot practically avoid.<\/p>\n\n\n\n

Royalty Rate Analysis for Divisional Portfolios<\/strong><\/h3>\n\n\n\n

When licensing a drug patent portfolio that includes divisionals, the royalty rate structure should reflect the layered nature of the IP. A compound patent license covers the right to make, use, and sell the active ingredient; a formulation divisional license covers specific dosage forms; a process divisional license covers specific manufacturing steps. These are economically distinct licenses, and bundling them at a single royalty rate obscures the value allocation in ways that complicate both negotiation and financial reporting.<\/p>\n\n\n\n

Royalty rates for pharmaceutical patent licenses range widely by claim type. Compound patents for approved drugs with remaining exclusivity typically command 4-8% royalty rates on net sales. Formulation patents command 1-4%, reflecting the higher design-around feasibility. Manufacturing process patents command 1-3% but may be valued differently where the process directly determines product quality characteristics relevant to regulatory approval. Method-of-use patents covering major indications command 2-5% where carve-out is commercially impractical. These ranges are reference points derived from public settlement disclosures and litigation outcomes, not fixed benchmarks, and they shift based on exclusivity remaining, market size, and the specific claim strength.<\/p>\n\n\n\n

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Key Takeaways: Challenger and Due Diligence Strategy<\/strong><\/h2>\n\n\n\n

FTO analysis for a divisionally protected drug must map the full patent family, not just the Orange Book listing, and must classify each patent by design-around feasibility and IPR vulnerability. IPR petitions against divisional patents that rely on prior art from the same patent family have higher institution rates; first petition quality is critical because of the serial petition bar. Royalty rate structures for divisional portfolios should be negotiated by claim type rather than bundled at a single rate, since compound, formulation, process, and method-of-use claims have materially different economic value per percentage point of royalty.<\/p>\n\n\n\n

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The Future of Divisional Patent Strategy<\/strong><\/h2>\n\n\n\n

AI-Assisted Patent Prosecution and Portfolio Management<\/strong><\/h3>\n\n\n\n

Machine learning tools applied to pharmaceutical patent prosecution have moved from experimental to commercially deployed in the past three years. The most mature applications cover prior art search acceleration, claim drafting optimization based on historical allowance data, and IPR prediction modeling that scores the vulnerability of issued patents to PTAB challenge before the petitioner files. For divisional portfolio management, AI tools are beginning to automate the mapping of dependent claims across related patent families, identifying potential claim overlap between parent and divisional that could generate ODP risks or prosecution history estoppel issues.<\/p>\n\n\n\n

The strategic implication for pharma IP teams is that the information asymmetry between originators and generic challengers that historically favored originators is narrowing. A mid-size generic manufacturer with access to AI patent analytics tools can conduct a scope of coverage analysis on a complex divisional thicket in a fraction of the time and cost that the same analysis required five years ago. Originators who do not invest in equivalent analytical capabilities to audit their own portfolios for vulnerabilities before challengers find them are operating with an outdated intelligence model.<\/p>\n\n\n\n

Legislative Proposals Targeting Secondary Patents<\/strong><\/h3>\n\n\n\n

Several legislative proposals pending in the U.S. Congress as of early 2026 would materially affect divisional patent practice. The proposed Affordable Prescriptions for Patients Act, in its most recent Senate version, would limit the number of Orange Book-listed patents per drug to the compound patent plus a defined maximum number of secondary patents, with the specific limit subject to negotiation. A separate proposal would require NDA holders to disclose all patents in the same family as any Orange Book-listed patent, including non-listed manufacturing process and non-approved-indication method-of-use patents, as a condition of maintaining the 30-month stay on any listed patent.<\/p>\n\n\n\n

Neither proposal has reached the Senate floor as of this writing, but both have bipartisan support that has not been present in prior patent reform attempts. The practical effect of the patent-listing limit would be to force originators to select which divisionals receive Orange Book protection, concentrating litigation on the highest-value patents rather than distributing it across an expansive thicket. The disclosure requirement would, for the first time, make the full divisional family visible to generic challengers without requiring the exhaustive independent patent search that current practice demands.<\/p>\n\n\n\n

Global Convergence and the TRIPS Flexibilities Debate<\/strong><\/h3>\n\n\n\n

Section 3(d) of the Indian Patents Act has functioned as a template for secondary patent restrictions in developing markets. As of 2024, Brazil, Argentina, Ecuador, and several ASEAN markets have adopted or are considering similar provisions that require secondary patents to demonstrate enhanced therapeutic efficacy rather than mere physical or chemical novelty. This global trend toward restricting secondary patents in middle-income markets is structurally compressing the geographic scope of divisional patent value.<\/p>\n\n\n\n

For multinational pharma companies with significant emerging market revenue, the relevant analytical question is not whether their divisional portfolios are valid in the U.S. and Europe, but what percentage of projected future revenue is protected by divisionals that would be unenforceable in markets applying Section 3(d)-style analysis. As more drugs generate a larger share of revenue from middle-income markets, particularly under IRA price pressure on U.S. Medicare revenues, this geographic erosion of divisional value becomes a material factor in asset valuation.<\/p>\n\n\n\n

\n\n\n\n

Investment Strategy: The Forward View<\/strong><\/h2>\n\n\n\n

The most defensible divisional patent estates over the next decade will be those built on genuine technical novelty in manufacturing process and formulation claims, not on marginal polymorph variations or obvious dosing regimen modifications. Companies investing in next-generation manufacturing platforms, including continuous manufacturing, cell-free protein synthesis, and novel lipid nanoparticle delivery systems, generate divisional patent estates with stronger novelty and non-obviousness defenses precisely because the technical territory is less crowded.<\/p>\n\n\n\n

For institutional investors, the portfolio-level question is which companies have the IP filing infrastructure, the internal prosecution expertise, and the litigation financing capacity to maintain effective divisional portfolios in an environment where PTAB challenge rates, FTC scrutiny, and IRA price pressure are all simultaneously compressing the commercial value of secondary patent protection. Companies that have consistently maintained clean Orange Book listings with technically defensible claim sets, managed divisional prosecution with attention to ODP and file wrapper estoppel risks, and built biosimilar or generic entry timelines that hold up under investor scrutiny are the ones whose IP-derived exclusivity premiums are most likely to persist.<\/p>\n\n\n\n

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Key Takeaways: Forward-Looking Patent Strategy<\/strong><\/h2>\n\n\n\n

AI-powered IPR prediction and claim scope analysis tools are reducing the information asymmetry that historically favored originators in divisional patent disputes; IP teams that do not audit their own portfolios with equivalent tools are exposed. Pending U.S. legislation targeting Orange Book listing limits and disclosure requirements would, if enacted, materially change the thicket construction playbook by concentrating litigation exposure on a smaller number of high-value divisionals. The geographic erosion of divisional patent value in Section 3(d) markets is a quantifiable revenue risk for any drug where more than 20% of projected future sales come from India, Brazil, or ASEAN markets, and it should be modeled explicitly in asset NPV calculations.<\/p>\n\n\n\n

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FAQ<\/strong><\/h2>\n\n\n\n

What is the difference between a divisional patent and a continuation patent?<\/strong><\/p>\n\n\n\n

A divisional patent arises from a USPTO restriction requirement and covers inventions separated from the parent due to non-unity. A continuation pursues additional claims on the same invention as the parent without adding new matter. Both inherit the parent’s filing date, but the underlying prosecution trigger and the permissible claim scope differ in ways that affect IPR vulnerability and ODP risk.<\/p>\n\n\n\n

How does the Orange Book listing of a divisional patent affect generic market entry timelines?<\/strong><\/p>\n\n\n\n

Each Orange Book-listed divisional gives the NDA holder grounds to sue on a Paragraph IV certification, triggering an automatic 30-month stay of ANDA approval per patent per challenge. A drug with six listed divisionals can generate, in theory, up to six consecutive 30-month stays against a single ANDA challenger, though courts have shown increasing willingness to deny injunctions where the asserted patents are weak.<\/p>\n\n\n\n

What is obviousness-type double patenting and how does it affect divisional patents?<\/strong><\/p>\n\n\n\n

ODP is a judicially created doctrine that prevents a patent owner from obtaining a second patent with claims that are not patentably distinct from claims in an earlier patent by the same owner. Filing a terminal disclaimer defeats an ODP rejection but limits the divisional’s term. Divisionals that survive without terminal disclaimers preserve independent term, making them more valuable as litigation assets.<\/p>\n\n\n\n

How does the Inflation Reduction Act change the value of divisional patent exclusivity?<\/strong><\/p>\n\n\n\n

For small molecules, IRA negotiation eligibility triggers nine years post-approval regardless of patent status. Divisional years of exclusivity that fall after this trigger are subject to a government-negotiated price, reducing their commercial value relative to pre-trigger years. IP teams should calculate each divisional’s contribution to pre-trigger versus post-trigger exclusivity when assessing portfolio value.<\/p>\n\n\n\n

What is the most effective legal strategy for challenging a divisional patent thicket?<\/strong><\/p>\n\n\n\n

The most resource-efficient approach combines a thorough FTO analysis identifying the weakest-link divisionals, parallel IPR petitions on two to four high-priority Orange Book-listed patents, and a declaratory judgment action or Paragraph IV certification to lock in the litigation timeline. IPR petitions should be filed within the one-year window after service of any infringement complaint to preserve the PTAB pathway.<\/p>\n\n\n\n

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Patent data sourced from the USPTO Patent Full-Text and Image Database, the FDA Orange Book, and Unified Patent Court case registry. All revenue and valuation figures are derived from publicly available company filings, sell-side research, and published transaction databases. This article is for informational and analytical purposes and does not constitute legal advice.<\/em><\/p>\n\n\n\n

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