4. Gilenya
2013 Revenue:
$1.93 billion

Being first to market isn't everything, and Novartis ($NVS) has learned that the hard way when it comes to Gilenya. When the drug hit the market, it was the first-ever MS pill, but it's since been eclipsed--not by the second to market, Sanofi's ($SNY) Aubagio, but by Biogen Idec's ($BIIB) high-flying Tecfidera.

Safety concerns have weighed Gilenya down since its rivals hit the market. A slowed heart rate after the initial dose ranks among its potentially more serious side effects, as does the fact that it works as a powerful immunosuppressant. And in August 2013, the FDA sent out an alert that a Gilenya patient had developed a rare but often fatal brain infection, which the FDA is investigating.

Nevertheless, Gilenya still racked up $1.02 billion in the U.S. last year along with another $911 million in Europe, with worldwide sales swelling 62% in constant currencies over 2012's haul.

And the Swiss pharma is hopeful that some brain-atrophy data from earlier this year will help keep those tallies climbing. Back in May, presentations at the American Academy of Neurology meeting showed that Gilenya put the brakes on brain volume loss, slowing the rate by one-third versus either placebo or interferon. -- Carly Helfand (email | Twitter)

For more:
Novartis sees brain-atrophy data as an edge for MS pill Gilenya
No big thrill from Novartis in Q1, just a 'solid' $14B in sales
Novartis under U.S. scrutiny for Gilenya marketing tactics
Novartis aims new Gilenya campaign at young MS patients