The drug: Enbrel
The companies: Amgen/Pfizer/Takeda Pharmaceutical
Estimated worldwide sales 2012: $8.37 billion

Unlike Pfizer's ($PFE) Lipitor or Bristol-Myers Squibb ($BMY) and Sanofi's ($SNY) Plavix, which saw generic competition in the U.S. as soon as those patents expired, Amgen's ($AMGN) anti-inflammatory drug Enbrel wasn't staring down the barrel of a cheaper rival as its key patent wound down. One of the several companies developing a biosimilar version would have to win FDA approval first.

Those would-be copycats will have to wait a lot longer now. Enbrel was set to lose U.S. patent protection this month, until Amgen won a new patent that could shield the drug for another 17 years. That gives Amgen and partners till 2028 to reap Enbrel sales in the 5 different diseases for which it's approved.

Enbrel sales reached about $7.4 billion in 2011, $3.7 billion for Amgen and $3.7 billion for Pfizer, which markets the drug outside the U.S. and Canada. As the companies move toward an estimated $8.37 billion in 2012 sales, they're unwinding their marketing partnership, set to expire next October. Amgen took over field sales in the U.S. and Puerto Rico in July.

For more:
Pfizer, Amgen prepare to dissolve Enbrel partnership
Amgen's new Enbrel patent could delay biosims for 17 years
Enbrel beats rivals in rheumatologist survey