Biosimilar not interchangeable: Sandoz and Pfenex call for US FDA guidelines

By Gareth Macdonald contact

- Last updated on GMT

Biosimilar but not interchangeable: Sandoz calls for US FDA guidelines
Biosimilar but not interchangeable: Sandoz calls for US FDA guidelines

Related tags: Reference product, Food and drug administration, Fda

Sandoz has joined biosimilar developers calling on the US FDA to provide clear guidance on interchangability just a day after launching Zarxio, its Neupogen (filgrastim) copycat.

Zarxio debuted in the US yesterday (despite a last minute effort to prevent the launch by Neupogen developer​ Amgen), becoming the first biosimilar approved via the 351(k) pathway​ to reach the market.

But while Zarxio (filgrastim-sndz) is ‘biosimilar’ – which means it can be prescribed in place of the reference drug - it is not ‘interchangeable’ and cannot be switched at pharmacy level without physician intervention.

Whether a drug is interchangable is important.

According to research published in Health Affairs​ while biosimilars are likely to have a modest impact on the market – Sandoz’s product is 15% cheaper than Neupogen – interchangables are expected to dramatically reduce prices.

"Initially, modestly discounted biosimilars deemed noninterchangeable with the original products will compete to become the initial treatment of choice in new patients. Subsequently, a second market may be anticipated for those products able to meet the FDA’s higher standard for “interchangeability.” In that market, discounts may be more dramatic​."

One interpretation is that because pharmacists can swap originators for interchangables without input from the doctor, insurance companies could make them the only covered option.


In Europe – where Zarxio has been approved as Zarzio​ since 2009 – a ‘biosimilar’ designation means a drug is therapeutically equivalent to a reference product. The European Medicines Agency (EMA) does not consider​ ‘interchangability’ when making its assessment.

In contrast, the US FDA can designate a biosimilar product as interchangeable​ if a sponsor can prove it is “expected to produce the same clinical result as the reference product in any given patient​” and that switching between the two is safe.

The trouble is that the US Agency has yet to define how a sponsor must go about generating such proof and – as Sandoz never sought an interchangeable designation for Zarxio – drugmakers targeting the US market are no clearer after yesterday’s launch.

Sandoz told this publication: “The FDA has made strong progress over the last few years in making this a viable pathway. The three main outstanding topics are naming, labelling and interchangeability.

He added that: “We believe that having clear and science-based guidelines on all three topics will play an important role in broadening the impact of biosimilars in the US​.”


Sandoz’s comments fit with what San Diego, California-based biosimilar developer Pfenex said following the Zarxio launch.

Pfenex told us: "It is anticipated that companies may have to perform switching studies with the biosimilar and the reference product, but FDA has not provided guidance on the regulatory expectations for the approach.  It is expected that interchangeability guidance should be released by end of the year."

In August the FDA published draft guidelines on naming​. The Agency wants to assign a random four letter suffix to all biological products, originators and biosimilars, to allow for more effective pharmacovigilance while preventing unintended switching.

Zarxio (filgrastim-sndz) was assigned as a place holder label before the draft guidelines were published.

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