A biosimilar (also known as follow-on biologic or subsequent entry biologic) is a biologic medical product that is almost an identical copy of an original product that is manufactured by a different company. Biosimilars are officially approved versions of original "innovator" products and can be manufactured when the original product's patent expires. Reference to the innovator product is an integral component of the approval.
Unlike with generic drugs of the more common small-molecule type, biologics generally exhibit high molecular complexity and may be quite sensitive to changes in manufacturing processes. Despite that heterogeneity, all biopharmaceuticals, including biosimilars, must maintain consistent quality and clinical performance throughout their lifecycle. Follow-on manufacturers do not have access to the originator's molecular clone and original cell bank, to the exact fermentation and purification process, or to the active drug substance, but they have access to the commercialized innovator product. Overall, it is harder to ascertain fungibility between generics and innovators among biologics than it is among totally synthesized and semisynthesized drugs. That is why the name "biosimilar" was coined to differentiate them from small-molecule generics. A simple analogy, often used to explain the difference, is to compare wine with soda pop. It is harder to say objectively that two bottles of wine from two wineries are "sufficiently interchangeable," because of differences in yeast strain, weather, and year of grape harvest, than it is to say that two bottles of soda pop of the same flavor coming from two bottling plants are "sufficiently interchangeable" because they contain the same flavoring powder.
Drug-related authorities such as the EU's European Medicines Agency (EMA), the US's Food and Drug Administration (FDA), and the Health Products and Food Branch of Health Canada hold their own guidance on requirements for demonstration of the similar nature of two biological products in terms of safety and efficacy. According to them, analytical studies demonstrate that the biological product is highly similar to the reference product, despite minor differences in clinically inactive components, animal studies (including the assessment of toxicity), and a clinical study or studies (including the assessment of immunogenicity and pharmacokinetics or pharmacodynamics). They are sufficient to demonstrate safety, purity, and potency in one or more appropriate conditions of use for which the reference product is licensed and is intended to be used and for which licensure is sought for the biological product.
In case of a monoclonal antibody-containing medicinal product, such as Remsima, extensive physicochemical and biological characterization for it and its reference product Remicade was conducted to demonstrate their highly-similar properties. Therefore, EMA has granted a marketing authorisation for only a few biosimilars since 2006, including a monoclonal antibody, that was recently approved. Meanwhile, on March 6, 2015, the FDA approved the United States's first biosimilar product, the biosimilar of filgrastim called filgrastim-sndz (trade name Zarxio) by Sandoz.