What are biosimilars and are they important?

All prescribers will be familiar with the issues associated with the use of branded and generic 'chemical' medicines.(1) For biological products (e.g. epoetin, filgrastim), a biosmilar medicine is a new biological product that is similar to a medicine that has already been authorised to be marketed in the EU (the biological reference medicine).(2) Six biosimilar medicinal products are currently marketed in the UK-three versions of filgrastim (▾Nivestim, ▾Tevagrastim and Zarzio),(3-5) two versions of epoetin (Binocrit and Retacrit)(6,7) and one version of somatropin (Omnitrope).(8) Applications for biosimilar versions of follitropin alfa and infliximab are under evaluation by the European Medicine's Agency (EMA) Committee for Medicinal Products for Human Use.(9) In the future there may also be biosimilar versions of insulins, recombinant vaccines, interferons and monoclonal antibodies such as rituximab and trastuzumab.(10) It is estimated that about 50% of the current UK market for biological medicines by spend may be subject to biosimilar competition by 2019. In this article, we will consider the background to developing biosimilar medicines, how and why they differ from traditional generic medicines in their licensing requirements and the issues that may arise as they are introduced to clinical practice.