US drugmaker Encysive says it has received a nod from European regulators to market its hypertension drug Thelin (sitaxentan sodium), pushing shares in the firm up more than 11% to $4.60 in after-hours trading on the Nasdaq.

The news follows the thumbs up by an advisory panel last month, but the company is waiting for a formal letter from the European Commission before it will provide further details, it said in a statement.

Encysive’s shares have been on a rollercoaster since March this year, when the US Food and Drug Administration unexpectedly issued its first approvable letter for Thelin instead of the anticipated all clear, a move which swiped around 50% off the group’s share price a the time. This was followed by a second request for further information in July, again pushing shares down as investor confidence in the drug waned further.

But Encysive remains confident in the future of Thelin in the US, saying the matter raised by the FDA in its latest 'approvable' letter would not require any additional clinical trials, and that is a matter of judgment that does require negotiations with the agency to see if agreement can be reached.

One group basking in Encysive’s misfortune is Actelion, maker of rival drug Tracleer (bosentan), its stock enjoying a nice boost on news of Thelin’s delay. Sales of Tracleer were $335 million in the first half of this year, but had been expected to come under pressure in the second half on competition from Thelin as well as Pfizer's Revatio (sildenafil) and Myogen's ambrisentan, also due for approval in the USA before the end of the year.

Thelin has been tipped as a $200 million product at peak.