Sales of GlaxoSmithKline's Advair/Seretide could be under threat after regulators in Sweden issued a light for a copycat version of the blockbuster lung drug, paving the way for its launch in several other European countries.

Sweden - acting as reference state under Europe's decentralised approval procedure - actually gave the go-ahead for Greek firm Elpen's generic form of Advair (salmeterol/fluticasone) last month, according to Reuters, but the decision seems to have been kept quiet by all involved.

Advair, which is marketed for asthma and chronic obstructive pulmonary disorder, pulls in sales of over £5 billion for GSK every year, but the company seems to be relatively unfazed over the potential impact Elpen's product might have on its drug's turnover. 

Crucially, despite containing the same active ingredients, the inhaler devices used for their delivery are quite different between the two products, and thus GSK believes they "are not fully substitutable" throughout Europe, a spokesperson told the media.

Elpen's product has been sold in Greece since 2009 under the name Rolenium, but has only managed to capture around 9% of the market compared to Advair's 43% share, according to Reuters.

However, analysts are warning that GSK could see a 25% hit on Advair's sales next year following the wider launch of Elpen's drug and other copycat versions waiting in the wings, such as one being developed by Novartis' generics' arm Sandoz.