GlaxoSmithKline's Advair loses share to AstraZeneca's aggressive Symbicort discounts

Advair's throne is slowly eroding. With stepped-up competition from rival lung drugs--including AstraZeneca's ($AZN) Symbicort--GlaxoSmithKline's ($GSK) top-selling product, with $7.7 billion in 2012 sales, is losing share in the U.S.

As Bloomberg reports, Advair's hold on the respiratory market slipped to 61.6% for the week ended Jan. 24, compared with 67.2% for the last full week in October. Symbicort, a longtime Advair rival, now boasts 30% market share, while Merck's ($MRK) Dulera has accumulated 8.4%.

Symbicort has been duking it out with Advair for years. Dulera has been on the market in the U.S. since mid-2010. So what's happening now? Price competition, Bloomberg Industries analyst Sam Fazeli told the news service.

"Advair has been losing share to Symbicort, and to a lesser degree to Dulera, driven by the more aggressive pricing and rebating strategy from both Astra and Merck," Fazeli said. "It is still too early to see any meaningful impact from Breo."

Breo, of course, is Glaxo's brand-new entrant in the chronic obstructive pulmonary disease field, delivered via an inhaler dubbed Ellipta. According to Bloomberg, it has a 0.3% share, but it was just launched at the end of October. Anoro, GSK's other new respiratory med, won FDA approval for COPD in December.

Advair has kept its crown in COPD and asthma, despite the loss of patent protection in 2010. Its Diskus inhaler device is covered through 2016, however, and that has helped hold off generic competition. New FDA guidance for respiratory generics appears to favor copycat development, but even still, some generics makers figure winning approval would take years.

A few knockoffs have already won approval in European markets. AirFluSal Forspiro, from Novartis' ($NVS) generics unit Sandoz, captured a series of regulatory nods across Europe in recent months. It's now approved in Denmark, Germany, Romania and Sweden. AirFluSal isn't automatically substitutable for Advair, however, which is expected to hamper uptake.

Special Reports: The 15 best-selling drugs of 2012 - Advair/Seretide | New FDA drug approvals of 2013 - Breo Ellipta - Anoro Ellipta