Shares of US biotechnology group Encysive Pharmaceuticals leapt 35% to $5.82 at the close of play on Friday, as investors revelled in the news that European regulators have recommended approval of its anti-hypertensive therapy Thelin (sitaxsentan sodium).

The company’s shares have been yo-yoing since March this year, when the US Food and Drug Administration unexpectedly issued an approvable letter for Thelin instead of the anticipated all clear, a move which swiped around 50% off Encysive’s share price.

But things were soon on the up again after the dust settled and the company announced that it had responded to the agency’s requests for more information, although whether the FDA’s requests have been fully satisfied still remains to be seen.

The delay in US approval could substantially eat into - if not totally wipe out - the first-to-market advantage Thelin was expected to enjoy over its closest rival, Myogen's ambrisentan, which was granted a priority review by US regulators in March.

The company says it expects the European Medicines Agency to reach a decision on whether to open the door to Thelin for the treatment of pulmonary arterial hypertension – which affects around 100,000-200,000 people across the globe - within the next 90 days or so.