Novartis' (NYSE: NVS) Gilenya run as the only drug oral medication to slow the progression of multiple sclerosis has come to an end. The Food and Drug Administration approved Sanofi's (NYSE: SNY) Aubagio yesterday.

Being second to the market can be a tough spot, and if Gilenya's history is any indication, it will be hard to hit the ground running. In the second quarter, nearly two years after being approved, Gilenya's sales finally topped $250 million -- what it takes to annualize out to a blockbuster. When a disease has so many treatment options, doctors often take a wait and see approach to new drugs even when the new drug has some advantages, taken orally versus being injected or infused in Gilenya's case.

Aubagio might be preferred over Gilenya given the safety issues Gilenya has had, but on the efficacy side, it doesn't appear to be that great of a drug. In one clinical trial, Aubagio failed to beat Merck KGaA and Pfizer's (NYSE: PFE) Rebif, an injectable drug.

The biggest threat for Aubagio is actually behind it. The FDA is expected to rule on Biogen Idec's (Nasdaq: BIIB) oral multiple sclerosis drug, BG-12, in December. BG-12 has arguably much better efficacy than Aubagio.

Aubagio's niche might end up being the patients that can't tolerate the more effective drugs. Given the large number of patients and the high prices the drugs can fetch, even grabbing a small piece of the $10 billion -- and growing -- market could tally up to reasonable sales.

And Sanofi has another option to get some more of the market. The company is also working on gaining approval for another multiple sclerosis drug Lemtrada. Last month, the FDA asked the company to reformat the data in the application. A little embarrassing -- a pharma giant should know what charts and figures the FDA wants -- but it's only a minor delay and certainly easier to fix than running another trial.

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