Eloxatin - $1.2 billion


Company: Sanofi
2011 sales: $1.2 billion
Developers: Sanofi-Aventis and Debiopharm
FDA approvals: Colorectal cancer, 2002; adjuvant use in colorectal cancer, 2004; new formulation, 2005

Eloxatin managed to make the top 5 this time based on 2011, but 2012 may be another story. The drug goes off patent in August, and a slew of generics are already approved. In fact, those generics have already been on the U.S. market--and that's why Eloxatin saw a whopping 379% increase in sales over 2010.

Those generics--from Teva Pharmaceutical Industries ($TEVA), Hospira ($HSP), Sandoz et al--hit the market in 2009, after a U.S. court determined that copycats wouldn't infringe its patents. Sanofi ($SNY) fought that ruling, and in April 2010, settled with key genericsmakers, which promised to stop selling their versions June 30. So, for half the year, Eloxatin had the kind of generic competition it will face later this year.

Those rivals dented Eloxatin's sales 75% in 2010. Then, the drug surged back last year--the first full year it had market exclusivity since 2008. It was the Eloxatin drama--and other impending losses to generic erosion--that helped persuade Sanofi CEO Christopher Viehbacher to buy Genzyme last year. Genzyme's rare-disease drugs are biologics, and therefore copy-resistant, Viehbacher figures.

Eloxatin - $1.2 billion