Modifying a drug's label to state that it slows a disease, rather than treating its symptoms, might not seem like that big of a deal. But for Teva Pharmaceutical (NASDAQ:TEVA), making that change to the label on its Parkinson's drug, Azilect, could add hundreds of millions of dollars in sales per year.

Yesterday, the generic-drug maker, which sells a few branded products like Azilect and its multiple sclerosis drug, Copaxone, said that Azilect had met its primary endpoints of slowing the progression of Parkinson's disease. The company didn't release any data because it plans to present it at an upcoming scientific meeting.

If the company's smart, it'll get the data presented quickly. The label-changing process with the FDA and other regulatory authorities will probably take until next year, but because the drug is already on the market, getting the data in front of doctors now could boost sales immediately. According to Teva, Azilect would be the first drug to have a label that states that it slows the progression of Parkinson's.

Sales of Azilect have been growing quickly -- the drug saw a 50% jump in sales year over year in the first quarter -- but it's starting from a pretty small base, at just $120 million last year. The lackluster performance isn't surprising, since there are generic drugs available to treat Parkinson's disease, such as the generic version of Bristol-Myers Squibb's (NYSE:BMY) Sinemet -- which, ironically, Teva sells as well. Azilect also has to compete with big-name drugs like GlaxoSmithKline's (NYSE:GSK) drug for restless leg syndrome, Requip.

In addition to the jump in sales, Teva may also be able to push back the entry of generic drug versions of Azilect. The U.S. patents for the drug begin expiring in 2012, but the new label could garner Teva seven additional years of market exclusivity, if the FDA gives Azilect the "orphan drug" status that is awarded to drugs with small patient populations.

The additional sales of Azilect wouldn't move the needle much on Teva's $9.4 billion in annual revenue, but every little bit should help the company reach its goal of $20 billion by 2012.

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