Merck & Co and ALK-Abello are celebrating the US green light for their grass pollen allergy immunotherapy Grastek.

The US Food and Drug Administration has approved Grastek, an allergen extract in a sublingual tablet, for the treatment of Timothy grass pollen-induced allergic rhinitis with or without conjunctivitis. The thumbs-up was expected given that the FDA's Allergenic Products Advisory Committee voted unanimously to recommend approval at the end of 2013 but it does come with a boxed warning regarding severe allergic reactions.

Commenting on the approval, David Bernstein of the University of Cincinnati said that every grass pollen season, "many patients with moderate to severe allergic rhinitis experience nasal and ocular allergy symptoms at their worst while taking symptom-relieving medication". These patients often have multiple sensitivities, he added, noting that some of these patients may be candidates for immunotherapy, but decline allergy shots.

The immunotherapy was approved in Europe in 2006 where it is sold as Grazax and it is currently marketed in 16 European countries. Earlier this year, Grastek was launched in Canada.

The approval comes a couple of weeks after the FDA gave a green light for Stallergenes' Oralair, making it the first immunotherapy tablet available for the treatment of grass pollen-induced allergic rhinitis with or without conjunctivitis.

The FDA is also currently reviewing Merck and ALK-Abello's ragweed allergy Ragwitek. Following a positive recommendation from the agency's advisory committee, a final decision is expected before the end of the second quarter.