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Biosimilars to treat inflammatory arthritis: the challenge of proving identity
  1. Jonathan Kay1,
  2. Josef S Smolen2,3
  1. 1Division of Rheumatology, Department of Medicine, UMass Memorial Medical Center and University of Massachusetts Medical School, Worcester, Massachusetts, USA
  2. 2Division of Rheumatology, Department of Medicine 3, Medical University of Vienna, Vienna, Austria
  3. 32nd Department of Medicine, Hietzing Hospital, Vienna, Austria
  1. Correspondence to Professor Jonathan Kay, Division of Rheumatology, Department of Medicine, UMass Memorial Medical Center and University of Massachusetts Medical School, Memorial Campus, 119 Belmont Street, Worcester, MA 01605, USA; jonathan.kay{at}

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The introduction of targeted biological therapies has revolutionised the treatment of patients with inflammatory joint diseases. These medications are highly effective in reducing disease activity, improving physical function, and retarding or arresting the progression of structural damage. Their relative benefits and risks have been ascertained and contraindications to their use are well known. However, the high price of these drugs has limited their widespread application. The potential availability of biosimilar versions of these targeted therapeutics promises accessibility to biopharmaceuticals with similar efficacy and safety but at a lower cost.1 ,2 In this issue of Annals of the Rheumatic Diseases, the results of the first randomised, prospective clinical trials comparing a biosimilar to an original (or ‘innovator’) biopharmaceutical for a rheumatic disease indication, are published.3 ,4

A biosimilar is defined as a ‘biotherapeutic product which is similar in terms of quality, safety and efficacy to an already licensed reference biotherapeutic product’, in which similarity is defined as the ‘absence of a relevant difference in the parameter of interest’.5 In this context, it is important to note that there are complexities inherent in producing large proteins. A biosimilar must ensure similarity to the reference product with respect to many attributes, such as amino acid sequence, conformation, post-translational modifications, immunogenicity, affinity for its ligand or receptor, and function. However, it must be recognised that subtle process changes in the production of an innovator product inevitably occur over time and have resulted in variations between commercial lots, such as changes in the glycosylation profile of rituximab that resulted in more potent antibody-dependent cellular cytotoxicity in vitro.6 Many of the commercially available innovator biopharmaceuticals that are used now to treat patients could thus be considered to be biosimilars of the originally produced lots of those products, all …

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