GlaxoSmithKline’s non-inhaled, biologic therapy for a difficult-to-treat form of severe asthma is now a hair’s breadth away from US approval after regulatory advisors unanimously backed its use in adults, but not adolescents.

Mepolizumab is being developed as an add-on maintenance treatment for severe eosinophilic asthma in patients who experience exacerbations despite high-dose oral or inhaled corticosteroids (ICS) and an additional controller (such as long-acting beta-2 agonist), a group for whom there remain few treatment options.

The FDA Advisory Committee voted 14-0 that efficacy and safety data for mepolizumab support the drug’s approval in adults. The panel also voted that efficacy data provide “substantial evidence of a clinically meaningful benefit” in this population (14 yes, 0 no) and that safety in adults with severe asthma had been “adequately demonstrated” (13 yes, 1 no).

On the downside, the drug’s use in adolescents 12-17 years of age with severe asthma was not supported by the Committee (4 yes, 10 no). It concluded that efficacy (5 yes, 9 no) and safety (2 yes, 12 no) had not been adequately shown mostly because of the limited number of patients included, and said further data are needed in this sub-population where there is a high unmet need.

Administered by subcutaneous injection every four weeks, mepolizumab is a monoclonal antibody that inhibits interleukin 5 and thus reduces the number of eosinophils in the tissues, blood and sputum, high levels of which can trigger both asthma and symptom exacerbations. Analysts believe IL-5 products, which also includes Teva’s soon-to-be-filed reslizumab, could expand the asthma market by billions of dollars.