Is the 505(b)2 Pathway Viable for Biosimilars?

With regulators focused on streamlining the 351(k) biosimilar development, it makes sense to wonder if the 505(b)2 pathway is valid for biosimilar approval.

Can discussions about streamlining biosimilar development reach into abbreviated approval pathways for small molecules? Based on a Stat News webinar I attended yesterday, they already have. What exactly are the differences between the 351(k) pathway for biosimilar candidates and the 505(b)2 pathway for small molecules?

Biosimilar-Type Products Already Approved Through the 505(b)2 Pathway

The 505(b)2 pathway was used for some products that are considered by most as biosimilars today. For example, Basaglar, the first copy of insulin glargine, was approved in 2015 through this pathway; it was before insulins transferred to the biosimilar pathway for approval in 2020. Admelog was the first insulin lispro copy, approved in 2017 through the 505(b)2 pathway as well. However, Granix, the first filgrastim molecule launched that was not Epogen or Procrit, utilized the 351(a) pathway, meant for innovator biologics; it predated the implementation of the 351(k) route to approval.

With streamlining of biosimilar development—a major focus of regulators today—it makes sense to wonder if the 505(b)2 pathway is a valid goal for biosimilar manufacturers.

Infographic comparing 505(b)(2) drug approval and 351(k) biosimilar pathways

The 505(b)2 application pathway was implemented through the Hatch–Waxman Amendments of 1984. It was not meant as an abbreviated pathway for generics, but rather a streamlined way to bring new forms of existing innovative medications to market. These are commonly referred to as “follow-on” products. The basis for its use is that the innovator product on which the follow-on molecule is based has a truckload of patient experience proving its safety and efficacy. The manufacturer would simply have to show that its product was very much like the innovator. Its application could range from new formulations, strengths, to other modifications that wouldn’t be expected to affect the structure or anticipated effectiveness.

According to Drug Patent Watch, development cost of a 505(b)2 product might be anywhere from $8 million to $20 million, and the timeline to reach the market (not counting patent litigation) could be as short as 3 years. The 505(b)2 pathway allows a manufacturer to utilize the innovator product’s preclinical and clinical data, requiring little more than comparability studies and bridging pharmacokinetic studies to reach the FDA application stage. The FDA may still require a phase 3 trial, which would change the costs dramatically, but it appears attractive in any case.

Of course, biosimilars require a bit more consideration, as they are far more complex than small molecules, for which the 505(b)2 pathway was intended. With the push to streamline biosimilar development, including waiving the phase 3 trial mandate, eliminate separate testing for interchangeability (and eliminate the designation itself), and drop the need for bridging studies, it is not difficult to visualize movement in this direction.

The Difference With Insulin as a Biosimilar

Yet, insulin is a relatively simple biologic molecule. It has decades of use and clinical experience supporting its safety and efficacy. When the 505(b)2 pathway was used to approve Basaglar and Admelog, few considered this a big risk (it may have helped that the first biosimilars were already approved and in clinical use).

Biosimilars are not follow-on products, unlike typical 505(b)2 agents. Rather, biosimilar manufacturers strive to make their candidates as close a copy as possible to the innovator (but realizing an exact match is impossible). Logically, it might seem that the biosimilar approval process should be at the same level of proof as the 505(b)2 pathway. No, that can never be the case—the structure of biosimilars will always be a little different than the innovator agent. And the structure will always change a bit over time (as will the innovator biologic).

It is better, instead, that the 351(k) pathway is modified to reflect the real-life experience of the biosimilars approved to date by the FDA and the EMA, and that does provide ample opportunity for lowering the bar, and costs, of development.

This article was written by our Director of Content, Stanton Mehr. Stan has been writing commentary and reporting news about the biosimilar industry since the submission of the first biosimilar 351(k) application to the FDA 13 years ago. Since that time, BR&R has been tracking the US biosimilar marketplace, with the industry’s original, comprehensive and updated database of biosimilar filings with the FDA.

First Opdivo Biosimilar FDA Application Submitted by Amgen

Amgen became the first manufacturer to submit an application to the FDA for a nivolumab (Opdivo) biosimilar. It also was the first to be sued for patent infringement.

Last week, Amgen became the first manufacturer to disclose that they submitted an application to the FDA for a nivolumab (Opdivo) biosimilar. In doing so, Amgen also became the first manufacturer to be sued by the reference manufacturer Bristol-Myers Squibb for patent infringement.

The company disclosed the 351(k) application during a business presentation on September 10. Amgen’s product, ABP 206, is one of several publicly disclosed nivolumab biosimilar candidates. The company reported, “...for ABP 206, our biosimilar candidate to OPDIVO, our Biologics License Application with the FDA has been submitted and accepted for review. We expect an FDA action on that BLA by end of the year.”

Net 2025 US revenues for Bristol-Myers Squibb’s PD-L1 inhibitor were $5.9 billion. The intravenously administered drug was first approved in 2014 (and market exclusivity ends this year), and its main patent expiration is expected to expire in 2028. Bristol-Myers Squibb also introduced a subcutaneously administered version of Opdivo in 2024, which is approved only for specific cancers. Among other manufacturers who have publicly disclosed potential nivolumab biosimilars Sandoz, Xbrane, Henlius, and mAbxience, are in various stages of development.

Patent Infringement Suit Filed Against Amgen’s Opdivo Biosimilar

Within days of the announcement of Amgen’s FDA biosimilar application for ABP 206, Bristol-Myers Squibb initiated a lawsuit claiming infringement on at least 7 patents on their product. We estimate the earliest expected launch date for intravenously administered nivolumab biosimilars to be in 2029 based on a main patent expiration in late 2028. Based on past experience, the likelihood of a settlement between the two parties may be lower than for other prospective biosimilar manufacturers, as Amgen has been willing to go at-risk for launch in the past (specifically for its aflibercept biosimilar Pavblu, a product with a similar market size as nivolimumab).

Of further interest, Opdivo is often prescribed in combination with Yervoy (ipilimumab), which is also the focus of considerable biosimilar research (also involving Amgen). Amgen also disclosed during its business presentation that it intends to file its biosimilar application for ABP 234, its biosimilar candidate to compete with Keytruda, before the end of the year.

The Second Entyvio Biosimilar Is Under Review at FDA

On July 31, Fresenius Kabi and Polpharma Biologics announced that its 351(k) application was accepted by both the FDA and the EMA for PB016, a proposed vedolizumab biosimilar candidate to Entyvio

The second vedolizumab biosimilar candidate is now under review by the US FDA. On July 31, Fresenius Kabi announced that its 351(k) application was accepted by both the FDA and the EMA for PB016, a proposed vedolizumab biosimilar candidate to Entyvio lyophilized vial for intravenous administration.

PB016, in-licensed from Polpharma Biologics S.A., is a proposed biosimilar to IV vedolizumab, an integrin-receptor antagonist indicated for the treatment of adults with moderately to severely active ulcerative colitis and Crohn’s disease in adults.

“FDA and EMA acceptances for review of IV vedolizumab biosimilar marks important milestones in the development program and underscores our commitment to improving patient access to high-quality, affordable biologic medicines,” said Dr. Sang-Jin Pak, President Biopharma at Fresenius Kabi. “With IV vedolizumab, we are advancing our autoimmune biosimilars portfolio and taking another step toward providing additional treatment options for patients living with chronic inflammatory diseases.”

The first biosimilar biologic licensing application was submitted in June by Alvotech and Teva.

In Other Biosimilar News

Amneal closed on its purchase of Kashiv Biosciences, a deal which “combines Kashiv’s biologics research, development and manufacturing capabilities with Amneal’s commercial scale, establishing biosimilars as a major long-term growth pillar within the Company’s Affordable Medicines business.”

Biosimilar Bytes: Biocon’s Yesafili Launches and Dr. Reddy’s Rituximab Biosimilar Is Approved

Biocon announced the launch of its Yesafili biosimilar, in competition now with Pavblu, for the aflibercept market. Dr. Reddy’s and its marketing partner Fresenius Kabi have received FDA approval for its rituximab biosimilar.

Biocon Begins Marketing Its Aflibercept Biosimilar Yesafili

Shreehas Tambe, Chief Executive Officer and Managing Director of Biocon Limited, said, “The commercial launch of Yesafili in the United States is an important milestone in our efforts to improve access to high-quality biosimilar medicines. It strengthens our presence in ophthalmology and reflects our commitment to making advanced treatments more accessible and affordable for patients around the world.”

The second aflibercept biosimilar has reached the US market, as Biocon Biologics announced the launch of Yesafili. Initially approved in May 2024, along with a slew of other aflibercept biosimilars, launches were delayed by settlement agreements with the manufacturer of the reference product, Eylea.

Pricing information was not reported for Yesafili. Significant sales volume of the first marketed aflibercept biosimilar, Pavblu, was achieved with a relatively small wholesale acquisition cost discount (–16%). Amgen, in its second-quarter 2026 earnings, reported $280 million in US sales, putting it on pace to be the first billion-dollar biosimilar. It has largely driven Amgen’s overall biosimilar revenues, which are up 29% from the same quarter in 2025.

Dr. Reddy’s Readying Rituximab Biosimilar for Launch with Fresenius Kabi After FDA Approval

On August 1, 2026, Dr. Reddy’s Laboratories received FDA approval for its rituximab biosimilar. The brand name and nonproprietary name suffix were not announced at the time of posting.

Dr. Reddy’s entered into a commercialization agreement with Fresenius Kabi to market the monoclonal antibody biosimilar in the United States.

The agent was known as DRL_RI in clinical trials, is already commercialized in the European Union in the United Kingdom. It is sold under the brand name Ituxredi in those markets. A launch date has not been announced for this fourth rituximab biosimilar approved by the FDA.

Currently, two biosimilars (Truxima and Ruxience) lead the rituximab category, each with 35% market share by volume, based on IQVIA data.

Tracking Two Bills to Remove the Clinical Efficacy Study Requirement for Biosimilar Development

Proposals in the House and Senate, both titled the Expedited Access to Biosimilars Act, may officially remove the FDA’s requirement for clinical efficacy studies for biosimilar candidates.

On July 15^th, a new bipartisan bill was introduced into the House of Representatives that would expand access to biosimilars by modernizing the FDA’s biosimilar approval process. This could be paired with a similar proposal just reaching Senate Committee discussion. Both of these proposals seek to reduce the cost of biosimilar development through squeezing out the need for comparative efficacy studies.

As reported earlier, the FDA in October 2025 announced a draft guidance that would achieve the same end, to remove the mandate for late-stage clinical efficacy trials for biosimilar manufacturers. However, a final guidance has not yet been released.

Introduced by Representatives Nick Langworthy (R-NY) and Kim Schrier, MD (D-WA), the Expedited Access to Biosimilars Act (HR 9661) could codify long-awaited regulatory changes to comparative trial expectations in the 351(k) biosimilar pathway.

According to a press release from Congressman Langworthy’s office, the act would eliminate unnecessary regulatory hurdles while preserving the FDA’s authority to require additional studies whenever scientifically warranted. This supports the October 2025 announcement of a draft guidance for removal of a mandate for phase 3 clinical efficacy studies for biosimilars. A key stipulation of the proposal would be a requirement for FDA to notify manufacturers early in the review process if additional late-stage comparative efficacy studies will be required. The aim would be to provide greater certainty around the clinical trial resources required for a successful biosimilar application process as well as avoiding unnecessary delays in the application process.

A number of associations have express support for the legislation including the Association for Accessible Medicines, the American Society of Health-System Pharmacists, and America’s Health Insurance Plans, among others.

The Senate’s 2025 Proposal

A Senate proposal by the same name (S.1414), introduced in April 2025 by Senator Rand Paul (R-KY), seeks largely the same goals. It has languished in the Committee on Health, Education, Labor, and Pensions, without additional cosponsors, until now. A committee meeting is scheduled for July 22 to finally consider this legislative proposal. It has one co-sponsor (Sen. Mike Lee, R-UT).

We’ll be monitoring whether the Expedited Access to Biosimilars Act can break through for an eventual debate and vote on either the House or Senate floor.

When is a Biosimilar a Biosimilar?

In 2026, is the definition of a biosimilar the same for countries’ drug regulatory systems around the globe? A recently published scoping survey attempted to answer the question.

Although there has been a decade of interest in moving towards global biosimilar regulatory standards, we first must answer a more foundational question: Is the definition of a biosimilar the same worldwide?

You may suspect that the answer is obvious, but then again, why are we asking it? Is it a trick question? Years ago, the answer was not so simple. Those of us covering the biosimilar field in the 2010s will recall that some Indian companies, for example, were producing what might be considered “follow-on” medicines by the FDA’s regulatory standards, but were promoting them as biosimilars.

No Guidances by FDA on Follow-on vs. Biosimilar Products

The FDA’s own regulatory definition was not set in stone: Basaglar, the second insulin glargine product to receive FDA approval, is a biosimilar but technically not a biosimilar. Even today, there may be some confusion as to whether Basaglar is considered a biosimilar or a follow-on product. It was indeed approved by the FDA under a 505(b)2 application, principally because insulins were not considered eligible for the 351(k) approval pathway until 2020. The FDA would probably support that it is clinically equivalent to Lantus in any way that matters. Yet, from a regulatory perspective, it was not evaluated as part of the biosimilar pathway, so it cannot be designated a biosimilar.

The same can be said for Granix, the second filgrastim product approved by the FDA, which underwent its approval process before the 351(k) was implemented (and under which Zarxio was licensed). It is important to note that the FDA itself has not tried to improve clarity by announcing retrospectively that these agents can be considered either biosimilar or an equivalent.

A Survey of Biosimilar Definitions

So, is a biosimilar a biosimilar throughout the world? An article published in JAMA Health Forum described a survey of 19 countries’ biosimilar regulatory guidelines. These included 12 with emerging and developing economies and 7 with advanced economies, according to the World Health Organization classification. The authors, from the University of San Francisco and GlaxoSmithKline, found that most countries define “biosimilarity as the absence of differences in the medicine’s quality, safety, and efficacy compared with the RP. Sixteen countries explicitly required comparability exercises to demonstrate biosimilarity, and 13 countries specified that the same RP must be used in these studies.

“Of the 19 countries in the study sample, 17 (89%) have adopted the WHO’s biosimilar terminology; the exceptions were Indonesia, which uses the term follow-on biological in addition to biosimilar,and Tanzania, which uses the term similar biotherapeutic product. A total of 17 countries (89%; except India and South Korea) define biosimilarity according to the absence of differences in quality, safety, and efficacy between the biosimilar and the reference product, although in some countries (Egypt, Turkey, UK, and US), this is heavily implied rather than explicitly stated. Most countries (n = 16 [84%]) require comparability exercises (by definition), but 3 (Mexico, Indonesia, and China) do not explicitly include this requirement.”

The authors also stated that all advanced economies waived the need for clinical efficacy and immunogenicity testing when justifiable, but guidelines from emerging and developing economies differed on clinical study waivers.”

Interestingly, one of the areas of least consensus is that of biosimilar naming and labeling guidance provided. Countries such as France, Germany, Japan, and South Korea do not specify any requirements, whereas the UK, US, and Canada do, among the WHO advanced economic sector. Among countries in the emerging and developing economic region, China and Mexico do have naming and labeling guidelines, whereas Brazil, India, and Indonesia do not. The area of greatest agreement seemed to be in acceptance of extrapolation, with all but Saudi Arabia among the surveyed countries with published extrapolation guidelines.

Scoping surveys such as this are necessary steps in a march towards global regulatory standards for biosimilars. They show not only how far we’ve come in reaching basic agreements, but also how far we need to go. Perhaps, most importantly, they show us areas where a push for global standards would have the least likelihood of success.