The decision by Sepracor to in-license the US marketing rights to inhaled corticosteroid Alvesco caps a four-year commercial and regulatory odyssey for the asthma drug.

Alvesco was approved earlier this month for maintenance and prevention of asthma after a long delay at the FDA, which issued an approvable letter in 2004.

Sepracor expects to launch Alvesco in the second half of the year. As part of the deal, the firm paid Nycomed $150 million up front. It will pay unspecified royalties on sales, plus up to $280 million in milestones. Nycomed is retaining all rights to Alvesco (ciclesonide) outside the US and has partnered with Teijin Pharmaceuticals in Japan, where Alvesco was launched in 2007.

The drug has seen multiple handoffs. Ciclesonide developer Altana Pharma was purchased last year by Nycomed for $6.8 billion, after which Altana launch partner Sanofi-Aventis transferred the Alvesco rights back to Nycomed. That left the privately held Swiss firm, which lacks a US sales force, with no way to bring Alvesco or its cousin Omnaris (a nasal spray formulation of ciclesonide for treating allergic rhinitis approved in 2006) to market.

Sepracor plans to launch Omnaris this spring, adding to a respiratory portfolio that also includes COPD/asthma treatment Xopenex and Brovana, approved for COPD.

It’s not out of the woods yet, though, say analysts. “[B]oth the asthma and allergic rhinitis markets are crowded, with significant generic competition, and it is not clear how ciclesonide is differentiated from other corticosteroids,” wrote Friedman Billings Ramsey analyst David Amsellem in an investor note today.

Once-a-day ciclesonide dosing is an advantage over twice-daily inhaled corticosteroids budesonide and fluticasone. But fluticasone, the active ingredient in GlaxoSmithKline’s Flonase, went generic in 2006 and accounts for roughly 45% of prescriptions, Amsellem pointed out. And for asthma, GSK’s Advair is widely used in the maintenance setting and could become generic in 2011.