Serial Patent Litigation for Pharmaceutical Products

Patent disputes among brand-name, generic and biosimilar product manufacturers are notoriously complex due not only to the technology at issue, but also the interplay of litigation with Food & Drug Administration (FDA) approval. Adding to this complexity is the increasingly common occurrence of multiple, sequential patent infringement proceedings involving the same drug product and the same parties, referred to as “serial patent litigation”. In addition to increasing litigation time, costs and risks, the impact of serial patent litigation extends well into the marketplace in the form of delayed or deterred generic and biosimilar entry, which ultimately influences drug prices, innovation strategies and competition. Counsel and business professionals should be aware of the potential implications not only for the litigation landscape but also for the pharmaceutical market.

Regulatory framework for generic drug and biosimilar entry

Pharmaceutical companies seek patent protection on a range of characteristics covering a drug product. It is common for a single product to be protected by patent claims covering not only the active ingredient, but also the compilation of active and inactive ingredients (ie, the formulation), physical characteristics of the active ingredient (eg, its three-dimensional structure) and methods of using the product (eg, an indication or dosing regimen). These patents often come in waves – a first wave to obtain a patent covering the active ingredient to secure broad exclusive rights, with later waves to obtain patent protection for other aspects of the drug product like the formulation and methods of use.

Companies seeking to market generic and/or biosimilar versions of drug products associated with patent protection in the USA rely upon regulatory frameworks to facilitate early and fast resolution of patent disputes, with an opportunity for a limited amount of marketing exclusivity among other generic or biosimilar applicants.

To balance patent protection with market competition, Congress enacted a set of frameworks to accelerate the approval pathways for generic versions of small-molecule drugs and biosimilar versions of large, complex biologics through the Drug Price Competition and Patent Term Restoration Act of 1984 (“the Hatch-Waxman Act”) and the Biologics Price Competition and Innovation Act (BPCIA).

The Hatch-Waxman Act requires that any pharmaceutical company with an FDA-approved new drug application (NDA) identify to the FDA each patent that the company asserts covers the drug product (21 U.S.C. § 355(b)(1)(viii)). The FDA then lists those patents in connection with the drug product in the Approved Drug Products with Therapeutic Equivalence Evaluations (the “Orange Book”). In most circumstances, when a generic applicant submits its abbreviated new drug application (ANDA) to a given NDA, the generic applicant must certify to each patent listed under the Orange Book under one of four paragraphs in the Hatch-Waxman Act:

• paragraph I – no patent information in the Orange Book;
• paragraph II – the patent is expired;
• paragraph III – the generic applicant agrees to not market its product until expiration of the patent; or
• paragraph IV – the patent is not infringed by the generic applicant’s product and/or is invalid (21 U.S.C. § 355(j)(2)(A)(vii)(I)–(IV)).

When a generic applicant certifies to a patent under paragraph IV, the Hatch-Waxman Act establishes litigation procedures with the goal of resolving the patent dispute before the generic launches its competing drug product. If a patent issues and the NDA holder lists it in the Orange Book during or after the conclusion of a litigation with a generic applicant, the generic applicant must still provide a patent certification to that “late-listed” patent if the generic applicant’s ANDA has not yet been approved.

The Hatch-Waxman Act is unique in that it provides for a 30-month stay of FDA approval of the ANDA to allow the federal courts time to resolve the patent dispute. In a typical Hatch-Waxman litigation, there are no damages at issue because the ANDA is not yet approved by the FDA, and thus there is no generic product on the market. Serial patent litigation can disrupt the usual litigation procedure and the visibility of the patent landscape by not only introducing litigation that extends beyond the 30-month stay, but also potentially giving rise to injunction proceedings and monetary damages if a generic product launches (or is prepared to launch) before resolution of all patent disputes.

The biologics counterpart to the FDA’s Orange Book is the Purple Book Database of Licensed Biological Products (the “Purple Book”). The BPCIA provisions do not require a formal patent certification but instead provide for a series of procedures to identify which patents should be litigated (including a “patent dance” between the brand-name drug sponsor and biosimilar applicant) (42 U.S.C. § 262(l)(4)–(5)). Biosimilar patent litigation has distinct considerations, particularly in the context of serial patent litigation, because the patent dance is optional and the average number of patents potentially covering the branded product is significantly higher than in Hatch-Waxman litigations. In addition, the BPCIA already contemplates a “second wave” of litigation if the biosimilar applicant provides notice of commercial marketing (42 U.S.C. § 262(l)(8)).

Scenarios leading to serial patent litigation

While the Hatch-Waxman Act and BPCIA provide abbreviated avenues for market entry of generics and biosimilars, the strategic assertion of a series of patents in litigation can turn what might have been a sprint into a marathon. Serial patent litigation can arise from a number of scenarios. Here, the focus is primarily on one of those scenarios that is currently on the rise – when the patent-holding brand company initially asserts infringement of patents listed in the Orange Book and later obtains a series of secondary patents via continuation applications that are part of the same “patent family” as a previously asserted patent.

A “patent family” is created when one patent application is used as the basis to support subsequent patent applications directed to the same technology. In pharmaceutical patents, the “parent patent” from which the continuation (or “child”) patent arises is generally directed to an active compound, formulation and/or a method of treatment. The continuations may claim secondary features of that technology, such as alternative formulations or methods of use for the compound that were disclosed but not claimed in the parent patent, or narrower species that were originally part of broader generic claims. Because continuations are filed and prosecuted later in time, the brand company can assess the product landscape and leverage the outcome of prior litigation to build its patent portfolio. There is currently no limit on the number of continuation applications that can be filed in the United States Patent and Trademark Office (PTO).

Seeking continuation patents in drug patent families is increasingly common as a means of expanding the scope and duration of Hatch-Waxman and BPCIA litigations. When litigation over the parent patent is ongoing, it is common for continuation patents to be issued and consolidated in the existing case. While consolidation can streamline some of the complications that arise from serially asserted patents, it does not abate the resulting increase in the number of asserted claims, which may require additional discovery and extensions to the schedule to fit within the existing case. Similarly, continuations can be prosecuted during the pendency of litigation over the parent and then asserted in a new action should the brand company obtain an unfavourable outcome at an injunction proceeding or trial. Because a continuation application cannot disclose or claim material that was not in the parent patent, it can take less time to prepare and move faster through the examination process than its parent, especially if the applicant requests prioritised examination from the PTO.

Illustrative cases

In 2026, scenarios similar to the examples provided below, where waves of litigation ensue as a result of a patent-holding brand company asserting a series of patents involving the same drug product and same defendant(s), can be expected. As these cases demonstrate, multiple waves of serial patent litigation can take many years to navigate.

Latisse® (bimatoprost)

Over a 15-year span, the brand company has brought multiple lawsuits regarding Orange Book-listed patents for its eyelash treatment product.

• In 2010, the brand company filed a first lawsuit (“Latisse I”), alleging infringement of three patents against multiple generic filers. One patent was dropped from litigation, and in 2014, the Federal Circuit found that the two remaining asserted patents were invalid.
• In 2012, the brand company filed a new lawsuit (“Latisse II”) alleging infringement of three newly issued patents related to the patents asserted in Latisse I. In 2015, the district court held that the newly asserted patents were substantially the same as the patents invalidated under Latisse I and invalidated the newly issued patents for the same reasons as in Latisse I, holding that the brand company was barred from contesting the invalidity of the asserted patents.
• In 2014, the brand company filed another lawsuit (“Latisse III”) against the same generic filers in Latisse I, alleging infringement of two patents related to the patents asserted in Latisse I. One patent was later dropped from litigation, and in 2015, the district court held that the remaining asserted patent was invalid and that the brand company was barred from contesting the invalidity of that patent. The Federal Circuit affirmed the decision on appeal.
• In 2017, the brand company brought a fourth infringement case (“Latisse IV”) after one of the generic filers launched its product, this time seeking a jury trial and damages for infringement of a patent related to one asserted in previous litigation. The jury found in favour of the brand company and awarded damages. This decision is currently pending on appeal.

Cabometyx® (cabozantinib)

Over the past seven years, the brand company has filed multiple lawsuits against a generic asserting the Orange Book-listed patents for a cancer-treating drug.

• In 2019, the brand company filed a first lawsuit (“Cabometyx I”) against a generic filer, alleging infringement of one patent. In 2020, the brand company filed a separate lawsuit against the generic filer, alleging infringement of two other patents, which was later combined with Cabometyx I. One patent was later dropped from the litigation, and in 2023, the district court found that the generic filer did not infringe the remaining two asserted patents.
• In 2022, the brand company filed a new lawsuit (“Cabometyx II”), alleging infringement of four newly issued patents. The brand company asserted another newly issued patent in a separate lawsuit against the generic filer that was consolidated with Cabometyx II. One patent was later dropped from the litigation, and in 2024, the district court found that the remaining asserted patents were not invalid and that the generic filer infringed three of the four asserted patents. This decision is currently pending on appeal.
• In 2025, the brand company filed another lawsuit (“Cabometyx III”) against the generic filer, alleging infringement of a newly issued patent related to the patent asserted in Cabometyx II that the generic filer was found not to infringe. Cabometyx III is pending in the district court.

Other examples of serial patent litigation include:

• Exparel® (bupivacaine) – six successive serial litigations, with seven patents asserted across eight complaints, spanning four years;
• Combigan® (brimonidine/timolol) – three successive serial litigations, with ten patents asserted across seven complaints, spanning 13 years;
• Hetlioz® (tasimelteon) – three successive serial litigations, with 16 patents asserted across 33 complaints, spanning eight years and still ongoing; and
• Korlym® (mifepristone) – one serial litigation, with nine patents asserted across five complaints, spanning eight years and still ongoing.

Expectations in navigating serial patent litigation

Serial patent litigation can significantly extend the litigation timeline and increase the cost, risk and uncertainty that pharmaceutical companies endure in this already-complex litigation arena. In the face of an expanding patent landscape with no clear end in sight, generic and biosimilar applicants may be compelled to settle with the brand companies. This outcome can delay and deter generic and biosimilar competition, which ultimately can impact drug prices.

When these prolonged legal battles extend past the FDA’s approval of generic and biosimilar products, applicants face the critical decision of whether to launch “at risk” despite the ongoing litigation, potentially exposing them to costly injunctive proceedings that could halt sales and ultimately bring damages into play. Because of the high bar for obtaining a preliminary injunction, brand companies should also be mindful of the potential for at-risk launches when employing the serial patent strategy.

Generic and biosimilar manufacturers should keep a close eye on pending patent applications related to drugs currently in litigation and plan for potential delays in case schedules should applications ultimately issue as patents. In ongoing litigations, they should also assess the court’s local rules and/or preferences to determine if the court permits or encourages a reduction in, or limit on, the number of asserted patent claims. Reducing the number of asserted claims can ease the burden of invalidating near-duplicative or overlapping claims brought into the case by continuation patents. When settling cases, generic and biosimilar manufacturers should also be cognisant of settlement terms that would allow the brand-named company to file subsequent suits alleging infringement by the same generic or biosimilar product of newly issued patents.

Conclusion

The pharmaceutical industry will continue to see a rise in serial patent litigation. While this strategy can serve to protect innovation and intellectual property rights, it raises questions about the broader impact on market competition, drug access and healthcare costs. Understanding these trends will be crucial for assessing the future landscape of pharmaceutical litigation.