Merck KGaA/Pfizer
Projected 2018 sales:
$1.766 billion
2012 sales: $2.433 billion

Merck KGaA's MS drug Rebif has been instrumental in helping the company return to a solid financial footing. In May, the German drugmaker, which has been slashing jobs and closing facilities to pinch pennies, said it would meet its 2014 sales and earnings targets--a year before it was expected to reach those goals. Bestseller Rebif was no small part of that effort, with sales up by 6% for the period thanks to higher U.S. pricing and increased volume in Europe.

Rebif has held its own despite an onslaught of new MS drugs coming to market in varying forms; Sanofi's ($SNY) oral drug Aubagio, for instance, failed to beat out the injectable Rebif in reducing the risk of treatment failure. But Merck's ($MRK) drug may soon find itself in a showdown with a newcomer. Last November, Sanofi's ($SNY) Genzyme group posted new data in support of its drug Lemtrada, which it hopes to make a leading therapy for multiple sclerosis.  

In a head-to-head study, Lemtrada was better at reducing the annualized rate of relapses. Patients treated with Lemtrada also showed an improvement in disability scores, suggesting a reversal of disability in some patients. Lemtrada is also provided in two treatment courses, one every 12 months over two years, compared with Rebif's several-times-a-week administering, which should help Sanofi/Genzyme gain approval.

For more:
Fast cost-cutting puts Merck KGaA a year ahead on financial targets
Sanofi's Lemtrada beats Rebif in head-to-head showdown