US company Myogen got its second piece of good news this week, when the Food and Drug Administration granted its orally-active pulmonary arterial hypertension drug ambrisentan a priority review.

Earlier, Myogen licensed ambrisentan outside the USA to pharmaceutical major GlaxoSmithKline in a deal that brought it $20 million in upfront fees and up to $80 million in milestone and other payments, as well as royalties on sales.

Ambrisentan is an endothelin antagonist currently in Phase III testing for PAH, and results from the first pivotal study (ARIES-2) were unveiled in December. A second Phase II trial - ARIES-1 - is due to report in April and, if positive, should allow ambrisentan to be filed for approval in both the USA and Europe later this year.

Market research firm Datamonitor said in a report published last month that it expects the global PAH market to grow from $636 million in 2004 to just over $2 billion by 2014, driven by new product and formulation launches and increased treatment rates. Up to 75% of PAH sufferers are currently not recognised and treated, it estimates.

The report notes that the first oral drug for PAH, Actelion’s Tracleer (bosentan) has transformed the market but will come under significant pressure over the next few years from ambrisentan and other drugs such as Pfizer’s recently-launched Revatio (sildenafil), and Encysive’s Thelin (sitaxsentan sodium), currently awaiting approval in the USA.