Eculizumab biosimilars

Humanised monoclonal antibody of about 148 kDa with a hybrid IgG2/IgG4 constant region, chosen to avoid complement activation and Fc receptor binding, produced in a murine myeloma (NS0) cell line.

Binds complement protein C5 and prevents its cleavage into C5a and C5b, blocking formation of the membrane attack complex. In paroxysmal nocturnal haemoglobinuria this stops complement-mediated lysis of red cells; in atypical haemolytic uraemic syndrome it stops complement-mediated damage to the microvasculature.

Intravenous infusion; half-life about 11 days, with weekly induction then fortnightly maintenance to keep C5 fully blocked. Plasma exchange removes it, so supplemental doses are given after plasmapheresis.

600 mg weekly for four weeks then 900 mg every two weeks for PNH; 900 mg weekly then 1,200 mg every two weeks for aHUS and generalised myasthenia gravis, from 300 mg/30 mL (10 mg/mL) vials. Meningococcal vaccination before treatment is mandatory in every market.

• Paroxysmal nocturnal haemoglobinuria
• Atypical haemolytic uraemic syndrome
• Generalised myasthenia gravis, anti-AChR antibody positive
• Neuromyelitis optica spectrum disorder, anti-AQP4 antibody positive

Anti-eculizumab antibodies are rare. Comparative programmes are constrained by the rarity of the diseases: they rely on analytical similarity, a pharmacokinetic and pharmacodynamic study in healthy volunteers using complement activity, and a comparative study in PNH with lactate dehydrogenase as the endpoint, typically fewer than 50 patients.

Soliris was licensed by FDA on 16 March 2007 (BLA 125166) and authorised in the EU on 20 June 2007 (EMEA/H/C/000791). Its price made it a target despite the small patient population, and the first biosimilars, Amgen's Bkemv and Samsung Bioepis's Epysqli, were authorised in the EU in April and May 2023 and approved by FDA in May and July 2024; Bkemv was interchangeable on licensure and Epysqli was designated in November 2025. Alexion's follow-on product, ravulizumab, has moved much of the market to eight-weekly dosing.

Sources: Purple Book (S016), EMA medicines data (S017), CDSCO import list (S012).

Eculizumab is the model for biosimilars of ultra-rare-disease biologics: tiny trials, a pharmacodynamic marker that regulators accept, and a price that justifies the programme even for a few hundred patients per country. Only two developers have done it. There is no Indian or Gulf biosimilar activity in the published lists; India's only entry is the originator's own import permission from 2025.