The question of interchangeability for biosimilars has haunted the US Food and Drug Administration since the promulgation of the Biologics Price Competition and Innovation Act of 2010. The FDA’s draft guidelines on interchangeability evolved very slowly, and the biosimilar industry had to work to (1) keep up with the guidelines as they gained clarity, (2) tirelessly wage war on misinformation as to what an interchangeable biosimilar actually represented, and (3) grasp the value of interchangeability as a for-profit enterprise and whether to charge forward with the necessary clinical trials.
In this column, we have often addressed the interchangeability designation, and how it may be perceived. Leaders in the industry, like Hillel P. Cohen, PhD, Executive Director, Scientific Affairs, Sandoz, have hammered home strong arguments that interchangeable biosimilars are not “better drugs” than their noninterchangeable brethren. They are simply subject to additional switching studies to confirm their clinical similarity to the reference product. That does not mean they are more similar to the reference product than a standard biosimilar.
At the 2021 DIA Biosimilars conference held virtually this week, Dr. Cohen restated logic that may be obvious but less often discussed: if two biosimilars are deemed highly similar to the same reference product, those two biosimilars, through the Law of Transitivity, should be highly similar to each other.
Though logical, the concept of biosimilar-to-biosimilar interchangeability is not acknowledged on a regulatory basis. However, the potential for biosimilar-to-biosimilar switching is undeniably real.
Biosimilar-to-Biosimilar Switching Likely to Occur
A large proportion of patients receiving chronic therapy with biologics will no doubt change health plans or insurers over time. This happens voluntarily (e.g., they may choose a lower-price plan from year to year) or involuntarily (i.e., their employer changes the plan offering from one year to the next). These plans utilize their own drug formularies. Considering the launch of perhaps eight adalimumab biosimilars in 2023, health plans will likely prefer different preferred adalimumab products, based on the contracting offers they receive or the characteristics of the biosimilar (e.g., citrate free, high-dose formulation, interchangeable). The same can be said for insulin products, infliximab, ranibizumab, and even chronically used oncology agents. Assuming that is the case, biosimilar-to-biosimilar switching may be somewhat common in 2025.
Is that an issue? Likely not, said Dr. Cohen. He believes that any immunogenicity concern is a hypothetical argument, “and no empiric evidence exists to support the concern. Furthermore, no data has been published to support immunogenicity on a mechanistic basis.” The biosimilar is highly similar not only in efficacy and safety but also with regard to immunogenicity.
What the Data Say
Most of the available data on biosimilar switching comes from Europe, where biosimilars have accumulated over 2 billion patient treatment-days of exposure. Countries adopt whichever biosimilar has the lowest price, based on tendering systems. This may mean that more than one biosimilar is accepted, and these tenders can change from year to year. The regulatory concept of interchangeability does not exist in the EU, and switching may occur in both infusible as well as injectable agents.
Dr. Cohen pointed out that published studies of biosimilar-to-biosimilar switching, based on the European experience, amount to 12 trials, all of which used observational data. Two trials involved adalimumab, eight infliximab, one etanercept, and one involved rituximab. These totaled 1,223 patients. Additionally, 8 studies were reported as meeting abstracts, six of evaluated infliximab biosimilars, and one each for adalimumab and etanercept. Those trials totaled 1,295 patients. Although the studies varied in terms of their limitations and design rigor, they were consistent in finding no differences in patient clinical outcomes, immunogenicity, or pharmacokinetics and pharmacodynamics.
“From a scientific matter, we can trust biosimilar-to-biosimilar switching,” stated Dr. Cohen. “There have been no safety issues, and we’ll very likely have more (observational) data in upcoming years.” If the data continue to show no significant issues, “it would be reasonable to conclude that biosimilar to biosimilar switching does not have any clinical impact.”
Observational data will have to do here, as no biosimilar manufacturer would reasonably spend the money to conduct a randomized, controlled head-to-head trial with another biosimilar.
The Declining Value of Interchangeability Over Time
The inevitability of this discussion has a noteworthy effect: It lowers the value of an interchangeable designation over time. Consider the adalimumab situation, which is similar to one we posed a few years ago: A health plan decides to prefer biosimilar C, which is designed by FDA to be interchangeable to Humira®, around mid-2023. In doing so, the plan places an NDC block on the reference product, and moves to convert as many patients as possible to interchangeable biosimilar C. It achieves more than 80% conversion through substitution at the pharmacy or specialty pharmacy. However, the plan is offered a far better price in 2024 on biosimilar F, a noninterchangeable drug. Biosimilar C no longer has an interchangeability advantage. All of the patients who were converted from Humira were already converted. And biosimilar C is not considered interchangeable (by the FDA) with any approved biosimilar. Payers, however, will likely consider these agents freely switchable with each other, depending on how much weight the payer gives to citrate status and dose concentration characteristics of the products.
What does interchangeability mean in the realm of insulin products? We’ll delve into that rabbit hole in the next post.
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