GlaxoSmithKline has forged a $100 million alliance with Myogen to secure rights outside the USA to ambrisentan, a once-daily, orally-active drug for pulmonary arterial hypertension.

Denver-based Myogen gets $20 million upfront in the deal, with the remaining $80 million due to come from milestone payments. The US firm will also get royalties on sales of ambrisentan – estimated to be in the region of 25% - and will also market and distribute GSK’s injectable PAH drug Flolan (epoprostenol sodium) in the USA.

Myogen said the GSK deal would help it fund the development of its US salesforce and commercial organisation, well in advance of ambrisentan’s launch.

Ambrisentan is an endothelin antagonist currently in Phase III testing for PAH, and the 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.

Although Flolan remains a mainstay drug for PAH and is particularly useful in patients presenting with life-threatening symptoms, there has been a shift towards oral therapy with the launch of products such as Actelion’s Tracleer (bosentan) and Pfizer’s Revatio (sildenafil).