3. Remicade
The companies: Janssen (Johnson & Johnson), Merck, Mitsubishi Tanabe Pharma
Worldwide sales: $8.386 billion

Janssen's monoclonal antibody (mAb) therapy for rheumatoid arthritis (RA), Crohn's disease and other conditions is Johnson & Johnson's ($JNJ) best-selling drug by far. It generated more than $5.2 billion in sales for J&J last year. Its next best-selling product is oncology drug Zytiga, at about $1.698 billion.

Remicade is no slouch for Merck ($MRK), either, which has rights to the drug throughout Europe, Russia and Turkey. It generated $2.271 billion for Merck last year. The rest goes to Mitsubishi Tanabe Pharma, which sells it in Japan and parts of Asia.

While Remicade continues to grow, up 8.7% in 2013, the extent of its potential growth has been put into question by the approval of biosimilars last year by the European Commission. U.S. generic drugmaker Hospira ($HSP) and its biosimilar partner South Korea-based Celltrion got their versions, Inflectra and Remsima, approved for treating many of the same inflammatory diseases for which Remicade is used. It may take time to get physician buy-in for the biosimilars, but that could be helped by a comparison study being conducted by Norway for Remicade and the new biosimilars.

Merck will be the first to feel that pain because it sells Remicade in Europe, but the clock is ticking for J&J as well, with the U.S. patent set to go off in 2018. By then, it may be facing biosimilars from a host of makers who want a piece of the action. While biosimilars are not expected to undercut drug sales like small-molecule generics, Celltrion has said it will price its biosimilar at a 30% discount to Remicade. You can expect payers to jump on that bandwagon as soon as they feel justified in moving patients to a copy.

J&J and Merck are hoping Simponi, a new-generation rheumatoid arthritis drug that the two also share, will offset the sting from slowing sales of Remicade. Simponi did see a 50% jump in worldwide sales last year but at just $932 million, it still falls far short of Remicade's financial firepower.

For more:
Hospira, Celltrion achieve milestone in EU with OK for Remicade biosimilar
Norway to compare Hospira knockoff with J&J's Remicade to goose biosimilars market
J&J's Simponi Aria approved for RA as it heads for blockbuster stratosphere

-- Eric Palmer (email | Twitter)