Sandoz,  Novartis’ generics unit, has begun mid-stage study of a biosimilar version of Roche’s blockbuster antibody drug Rituxan/MabThera.

According to the company, the Phase II trial for the biosimilar version of Rituxan (rituximab) is focusing on the therapy of rheumatoid arthritis.

Sandoz said in a statement that  it has developed “a robust, high-yield and large-scale process for the production of biosimilar rituximab” over the last few years. To ensure biosimilarity with the reference product, “a comprehensive physico-chemical and functional analysis of the product was conducted using modern bioanalytic techniques, followed by further studies”. Data so far suggest that its version is “highly similar to the reference product, justifying initiation of clinical studies in patients”.

Jeff George, Sandoz global head,said: “This key development milestone demonstrates that Sandoz, the pioneer in biosimilar, is on track to maintain its global leadership position in the medium to long-term.

“With nearly 50% market share within the global regulated biosimilar market, and with three marketed products, Sandoz plans to continue to broaden patient access to essential high-quality biologics by consistently advancing our industry-leading development pipeline.”

Rituxan is a huge earner for Roche, and Novartis says it ranks among the top three biologics worldwide, with 2009 sales of $5.60 billion.

Other companies are working on a biosimilar of Rituxan, notably Teva Pharmaceutical Industries, while last week Spectrum Pharmaceuticals signed a pact with Viropro to develop a version of rituximab ahead of its US patent expiration in 2015.