The worldwide market for copies of biotech medicines will grow to $3.7 billion by 2015, from just $243 million in 2010, as a raft of branded drugs lose patent cover, according to market analysis firm Datamonitor.

Many drugmakers are seeing potential in the business of producing copycat versions of expensive biotechnology drugs as regulators draft new rules for their approval.

Because of the complexity of such drugs, which are produced through biological processes that generally involve recombinant DNA technologies, they are known as "biosimilars" rather than generics.

Europe has led the way in setting out guidelines for biosimilars but U.S. regulations are also in the works and Japan, too, is addressing the issue.

Impetus for biosimilars will come from the fact that more than 30 branded biologics with sales of $51 billion are set to lose patent exclusivity between 2011 and 2015, Datamonitor said on Monday.

A number of generic drugmakers have made biosimilars a priority for future growth, including Teva, Novartis unit Sandoz and Hospira. They are being joined by several branded drugmakers, such as Merck.

In their sights are current blockbuster biotech treatments from companies including Roche and Amgen.