The US Food and Drug Administration has now agreed to take another look at Shire's marketing application for its hereditary angioedema drug Firazyr, with a review date set for August 25.

The regulator had previously issued a complete response letter for the drug, which Shire took under its wing as part of its acquisition of Jerini in 2008, requesting additional information and thus forcing the drugmaker to undertake an additional Phase III trial.

But the extra work seems to have paid off; headline results from the FAST-3 trial reported back in December were positive, showing that patients with HAE given Firazyr (icatibant) experienced a significantly faster time to the start of symptom relief versus those taking a placebo.

HAE is characterised by recurring and sudden attacks of swelling in the skin (including hands, feet, face and genitals) or the mucous membranes (gastrointestinal tract, larynx or voicebox), which can be extremely painful and even fatal if the larynx swells up and causes suffocation.

According to the data presented, Firazyr induced a 50% reduction in a composite symptom score assessment in just 2 hours (median value) compared 19.8 hours for the control group, marking a highly significant difference and showing the drug's potential benefit for patients with this rare genetic condition.

Shire's drug has already received marketing clearance in 37 countries around the globe, and the company will no doubt be keeping its fingers crossed that the new safety and efficacy data is enough to finally open the door to the all-important US market.

If it does win a green light, Firazyr will be competing directly for market share with Dyax Corporation's Kalbitor (ecallantide), which has been available across the pond since 2009.