Shares in United Therapeutics shot up 30% in late afternoon trading yesterday as investors revelled in surprise news that US regulators have finally issued a green light for its oral blood pressure drug.

The US Food and Drug Administration has now cleared Orenitram (treprostinil) Extended-Release Tablets for the treatment of pulmonary arterial hypertension (PAH), but only for WHO Group I patients to improve exercise capacity.

The move, which follows two rejections by the regulator, marks the first time that the FDA has given the nod to an orally administered prostacyclin analogue for any disease, the firm noted.

According to Mark Schoenebaum at ISI Group, as quoted by Forbes, the approval has come as “an enormous surprise - arguably, one of the top 10 biggest upside surprises in the history of the biotech sector,” primarily because its treatment benefit is regarded as relatively small and no additional data had been submitted to the agency.

Approval was based on data from the primary efficacy study, FREEDOM-M, which showed that patients receiving Orenitram twice daily - an oral form of the firm's injectable Remodulin, improved their median six-minute walk distance by 23 meters as compared to patients receiving only placebo.

While the FDA's approval has narrowed the drug's target population significantly, United is currently carrying out another clinical study, data from which could help widen its reach, if successful.