7. Advair

GSK has been bracing for competition to its Advair for years, even as sales have fallen due to competition in recent years. (Eric Sagonowsky)

2018 U.S. sales: $1.42 billion
Disease: Asthma and COPD
Generics expected: February

GlaxoSmithKline’s Advair is finally facing off against generic competition. Mylan scored a late-January FDA nod and launched in February, ending a yearslong period of uncertainty about when the asthma and COPD inhaler would finally face copycats.

But it's not the beginning of Advair's decline from respiratory behemoth to a fraction of its former self. Even as Mylan and other Advair generic hopefuls suffered numerous delays at the FDA, respiratory competition and payers' discount demands took their toll. To hang on to market share, GSK served up aggressive discounts, and its big brand's sales began to erode.

In fact, it's been five years since Advair's sales peaked. Back in 2013, the drug brought in £5.27 billion globally. For 2018, the drugmaker reported £2.4 billion in Advair sales.

GSK lost its patent on the drug itself in 2010, but its Diskus inhaler technology was tough to copy, and the device itself didn't lose its IP shield until 2016. But even after that last patent fell away, generics makers were struggling to get their products through FDA review. Mylan suffered numerous rejections and delays before its January approval.

Now, Mylan has its chance to grab share away from GSK, and it launched in mid-February with a 70% discount to Advair's list price. But analysts were quick to point out that Advair's net price is far lower than its sticker, thanks to behind-the-scenes rebating. One analyst estimated that Mylan's generic list price is really just about 20% cheaper than GSK's brand after rebates and discounts. Mylan's own deals with payers could widen that gap to 40%, though, she added.

RELATED: Mylan finally crosses the finish line with long-awaited generic of GlaxoSmithKline's Advair

Mylan has its best shot at a market-share grab now, before more Advair rivals swoop in. Novartis, which has been gunning for an approval, recently said it expects a 2020 generic launch rather than 2019. And last year, the FDA rejected a copycat from partners Hikma and Vectura, asking for an additional clinical study.

After the approval, Evercore ISI analyst Umer Raffat predicted Mylan’s copycat could generate nearly $250 million in 2019, while Leerink Partners’ Ami Fadia predicted $170 million for the generic this year.

7. Advair