On Monday, Swiss drugmaker Novartis (NYSE:NVS) announced that it had received European Union marketing approval for its version of a multiple sclerosis (MS) drug that has long been marketed by Bayer.

The drug in question is Bayer's MS interferon treatment Betaseron, which Novartis will market as Extavia. It is one of the leading multiple sclerosis treatments on the market, and it has an interesting history involving several different drugmakers.

In 1993, Chiron received approval to market Betaseron in the U.S., and it out-licensed these rights to Schering AG. The Betaseron royalty and manufacturing revenue that Chiron received from Schering grew to be one of its most important revenue sources.

When Novartis finished its acquisition of Chiron in 2006, it triggered a change-of-control agreement with the drug, giving Schering the opportunity to buy out Chiron's manufacturing assets related to the compound. Novartis stalled on this agreement, however, and Schering sued. Before the lawsuit could be concluded or a manufacturing sale negotiated, fellow German drugmaker Bayer acquired Schering.

Last year, Bayer/Schering and Novartis finally concluded negotiations for the sale of the manufacturing facilities, after Bayer agreed to pay $200 million and help Novartis get its own version of the drug on the market. This was an important concession, because unlike most drugs, Betaseron is a biopharmaceutical, and it’s much more difficult to make a similar version of such a drug.

Sales of Betaseron were approximately $1.5 billion last year. Novartis will launch its version of Betaseron in the European Union next year, where it will face close interferon competitors like Biogen IDEC's (NASDAQ:BIIB) Avonex and Merck Serono's Rebif.

Novartis also just filed a U.S. marketing application for its version of Betaseron. It will likely have to go through the regulatory approval process for the drug again, despite owning Chiron (and even though the drug has been on the market for 15 years), because it is producing its version of Betaseron at new manufacturing facilities. As Genzyme (NASDAQ:GENZ) showed investors last month, getting FDA approval for a new biologics manufacturing facility can sometimes be tough. But the extra few hundred million dollars in annual drug sales will surely be worth it to Novartis.