4. Levemir

Levemir has long lived in the shadow of Sanofi’s Lantus, but it's also been putting up blockbuster sales for Novo Nordisk.

Company: Novo Nordisk
2016 U.S. sales: $1.82 billion
Drug class: Basal insulin

Levemir has long lived in the shadow of Sanofi’s megablockbuster Lantus, but that doesn’t mean it’s not a powerhouse in its own right. The basal insulin has chugged along, putting up blockbuster sales year after year for the Danish drugmaker, with $2.54 billion last year worldwide, $1.82 billion of that in the U.S.

The basal insulin category has been a tough one lately, however, as payers saw the opportunity to pit the contenders against one another for bigger rebates and discounts. That pressure has eaten into sales growth across the category, despite regular price increases that recently landed Novo, Sanofi and their chief diabetes rival, Eli Lilly, under a microscope.

Levemir is an aging product, however, and Novo has big plans for its follow-up med Tresiba, which launched in the U.S. last January. It’s a longer-acting basal insulin that Novo touts as a superior therapy in its class. As selling points, the company points out that Tresiba lasts 42 hours and has a profile that allows patients to dose at any time of day, and it has generated data showing that the risk of hypoglycemia, a much-feared side effect of insulin therapy, is lower for Tresiba than with Lantus, particularly nighttime hypoglycemia.

But while Novo builds up its case for Tresiba—and awaits an FDA decision on a beefed-up label that includes its hypoglycemia benefits—Levemir will continue to jockey for basal insulin share against Lantus, its follow-up Sanofi med Toujeo, and its new biosimilar, Basaglar, plus Eli Lilly’s entrants in the same class. And it’s growing in emerging markets, with a 46% increase in China last year and a 27% hike in the 153 other nations outside the big U.S., Asian and European countries.

4. Levemir