9. Ocrevus

Roche's Ocrevus grabbed an FDA approval in MS back in early 2017. (Roche)

Company: Roche
Used for: Relapsing or primary progressive multiple sclerosis
2019 sales: $3.79 billion

Few pharmaceutical markets are as jam-packed as multiple sclerosis, as Roche knows well. Still, its Ocrevus, after just two years on the market, has soared to blockbuster sales—but challengers loom in every direction. 

Ocrevus could add $970 million to its 2019 sales total of $3.79 billion in 2019, according to EvaluatePharma, potentially upping the drug's rake to $4.76 billion this year. 

For Ocrevus, which notched its first and only FDA approval—to treat both relapsing and primary progressive forms of MS—in March 2017, that growth is tied to a booming market that is increasingly chock full of blockbusters. 

RELATED: Ocrevus, Hemlibra offset Roche's biosim loss. But what about those lackluster Xofluza sales?

A smaller player like Merck KGaA's Mavenclad brought in just $358 million on the year, but it posted more than 250% growth from the previous year. A newer challenger, Novartis' Mayzent, notched just $17 million on the year.

But Ocrevus is the only one among them to sport a PPMS nod, and its RMS data impressed analysts, too. Its performance in trials has helped Roche offset copycats to its trio of oncology meds—Avastin, Herceptin and Rituxan—all of which faced U.S. biosimilars hitting the market this year. 

RELATED: Bristol Myers nabs long-sought FDA nod for Celgene's MS drug ozanimod, but pandemic delays launch

With competition already stiff, though, the biggest competition could still be ahead. The FDA recently approved Bristol Myers Squibb's Zeposia (ozanimod), an MS med that boasts megablockbuster potential of its own. EvaluatePharma predicted the product would hit $1.6 billion in sales in 2024, and Bristol management is expecting it to peak at $5 billion in annual sales.

But after the long-awaited approval, Bristol will have to keep waiting for the rollout. The company said it would delay Zeposia's launch due to the novel coronavirus pandemic "based on what’s in the best health interest of our patients, customers and employees."

9. Ocrevus