Biosimilars are required to have the same mechanism of action, route of administration and dosage form as the originator biological and not be meaningfully different with regard to safety, purity or potency. The US Food and Drug Administration (FDA) has thus far issued six draft guidance documents for biosimilars [3].

FDA defines an ‘interchangeable’ biological product to be ‘a product that has been shown to be biosimilar to the reference product, and can be expected to produce the same clinical result as the reference product in any given patient [4].

When biosimilars are approved by FDA, it is likely that only a select few will be deemed interchangeable, while most will simply be approved as members of the same drug class to treat the same conditions. In this respect, interchangeable and non-interchangeable biosimilar substitutions are roughly analogous to bioequivalent and therapeutic substitutions in generics, respectively [5].

The complexity of biologicals, and thus biosimilars, has enabled brand-name manufacturers to successfully lobby some US states to increase barriers for pharmacists to automatically substitute originator biologicals with biosimilars [6].

Some professional societies, patient groups and originator biologicals manufacturers, meanwhile, have urged FDA to adopt naming conventions that clearly distinguish biosimilars from originator products. Advocates for unique naming for biosimilars have claimed that if a common non-proprietary name were used, patients would not know which drug they are getting [7]. While advocates for biosimilars having the same international non-proprietary name as their reference products point to the fact that biosimilars have been on the market in Europe since 2006 with a proven safety record, and there have been no issues with traceability or pharmacovigilance [8].

The authors conclude that to enable formularies to recommend substitution with both interchangeable and non-interchangeable biosimilars further safety and effectiveness data are required. However, treatment initiation with biosimilars can both improve patient health outcomes and reduce healthcare spending.

Conflict of interest
AS Kesselheim’s (ASK) work is supported by an Ignition Award from the Harvard Program in Therapeutic Science. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors of the research paper [1] declared that they have read the journal's policy and declare the conflicts that ASK is a member of the Editorial Board of PLOS Medicine.

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References
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2.  Sarpatwari A, Choudhry NK, Avorn J, Kesselheim AS. Paying physicians to prescribe generic drugs and follow-on biologics in the United States. PLoS Med. 2015;12(3):e1001802.
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5.  GaBI Online - Generics and Biosimilars Initiative. Substitution of generics in the US [www.gabionline.net]. Mol, Belgium: Pro Pharma Communications International; [cited 2015 Apr 17]. Available from: www.gabionline.net/Biosimilars/Research/Substitution-of-generics-in-the-US 
6.  Derbyshire M. US state legislation on biosimilars substitution. Generics and Biosimilars Initiative Journal (GaBI Journal). 2013;2(3):155-6. doi:10.5639/gabij.2013.0203.040
7.  GaBI Online - Generics and Biosimilars Initiative. FDA’s public hearing on biosimilars draft guidances [www.gabionline.net]. Mol, Belgium: Pro Pharma Communications International; [cited 2015 Apr 17]. Available from: www.gabionline.net/Biosimilars/General/FDA-s-public-hearing-on-biosimilars-draft-guidances 
8.  GaBI Online - Generics and Biosimilars Initiative. Fight continues over biosimilar naming standards [www.gabionline.net]. Mol, Belgium: Pro Pharma Communications International; [cited 2015 Apr 17]. Available from: www.gabionline.net/Biosimilars/General/Fight-continues-over-biosimilar-naming-standards 

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