FDA opens abbreviated approval pathway for interchangeable biosimilars
The Food and Drug Administration has proposed a regulatory path for biosimilar biologics that are interchangeable with the reference product, paving the way for a new generation of less-expensive versions of these unique drugs.
But bringing an interchangeable biosimilar to market won’t be easy. The bar for interchangeability will be high, requiring that manufacturers prove switching between the new and older products is safe. And clinicians, while cautiously optimistic, aren’t thrilled with the industry payoff that could come with the designation: freedom for insurance companies and pharmacies to switch products at the dispensing level without requiring a new prescription.
The draft FDA guidance for industry, “Considerations in Demonstrating Interchangeability With a Reference Product,” arises from the Biologics Price Competition and Innovation Act of 2009. That section of the Affordable Care Act provides for abbreviated approval pathways for biological products that are demonstrated to be “highly similar” (biosimilar) to or “interchangeable” with an FDA-approved biological product.
The difference between these appellations is subtle but critical to the regulatory process – and perhaps to patient safety. Regulators recognize that the structure of these large, highly complex molecules can never precisely replicate the reference product. But to be labeled a “biosimilar,” developers must prove that the new product functions essentially the same; there can be no clinically meaningful differences in terms of safety, purity, and potency. Unlike a generic medication, a biosimilar can’t be substituted for its reference product at the pharmacy level. If a physician wants the patient on that biosimilar, the script must specify it.
Interchangeables jump a higher regulatory bar
An “interchangeable biosimilar,” though, would have to jump a higher regulatory bar. Not only must it produce the same clinical result as the reference product, it also must be benignly interchangeable with it, conferring no additional risk if a patient switches from the reference to the biosimilar and back again. A pharmacist could, if permitted by state law, substitute an interchangeable product for the reference product without going through the prescriber.
Like biosimilars, interchangeable products need not be tested in every disease for which the reference drug is approved, according to the document. Once they are proved safe for one indication, those data can be extrapolated to allow approval for the other indications as well. Nor do biosimilars need to prove efficacy per se, as their molecular similarity to the reference product ensures that they bind to the same receptor and exert the same therapeutic effect.
The biosimilar/interchangeable market has been slow to take off in the United States. There are no approved interchangeable biosimilars, and only four biosimilars – three of which were approved in 2016:
• Sandoz’ filgrastim-sndz (Zarxio).
• Pfizer’s and Celltrion’s infliximab-dyyb (Inflectra).
• Sandoz’ etanercept-szzs (Erelzi).
• Amgen’s adalimumab-atto (Amjevita).
Switching studies is the key to achieving the interchangeable designation, according to the FDA document. They must include at least two full switches between the candidate product and the reference product, which must be licensed in the United States.
But because these products are so structurally diverse, the FDA isn’t imposing a one-size-fits-all process on them. Instead, the molecular complexity and immunogenicity of each product will dictate its approval requirements.
Those with relatively low structural complexity, high molecular similarity to the reference product, and a low incidence of immunogenic adverse events may only need a single switching study to achieve the “interchangeability” designation.
The bar will be higher for a product with high structural complexity that is not as similar to the reference product, or which has been associated with immunogenic adverse events. For this product, FDA might also require extensive safety postmarketing data for the product as a licensed biosimilar, as well as a switching study.
Pharmacokinetics, pharmacodynamics, immunogenicity, and safety will be the primary endpoints of a switching study. Efficacy data are not necessary but can be used as supportive endpoints. Any safety signals in a switching study would raise regulatory eyebrows whether they came from the candidate product or the reference product. Since the study replicates what could happen if the two were used sequentially, it makes little difference from which product the event might arise.
“If an apparent difference in immune response or adverse events is noticed between the switching and nonswitching arms of the study ... it would raise concerns as to whether the proposed interchangeable product is interchangeable, regardless of whether the proposed interchangeable product or the reference product or the switching of the two products actually caused the event,” the document notes.
The E.U. vs. U.S. experience
The United States is only now getting a taste of what has become common fare in the European Union, said Angus Worthing, MD, chair of the American College of Rheumatology’s Government Affairs Committee. The European Medicines Agency approved its first biosimilar in 2006. Since then, 23 such drugs have come on the market, at an average price of about 30% less than the reference drug. Prices for some drugs have dropped as much as 70% in countries in which national health care systems abandoned the reference product in favor of the competing biosimilar, Dr. Worthing said in an interview.
