GlaxoSmithKline has been hit by the news that a German court has declared a key patent on its biggest-selling drug Advair/Seretide, sold in Germany as Viani, as invalid.

The Federal Patents Court in Munich has ruled that a patent on Viani (salmeterol/fluticasone), a treatment for asthma and chronic obstructive pulmonary disease, is not valid, specifically relating to the combination of the active ingredients. The court’s ruling, which follows a hearing in February, is a significant win for the four generic companies which brought the case – Mylan, Neolab, Novartis’ Hexal unit and Teva’s Ivax subsidiary.

Sales of Advair in the first quarter were up 9% at £1.26 billion, so clearly any generic versions will hurt GSK in the pocket but the company is not panicking. It notes that the decision relates solely to the German combination patent “and is not binding in any other jurisdiction” and the firm owns a number of other patents in the country, including the Diskus dry powder inhaler and HFA aerosol formulation patents which expire in 2011 and 2012 respectively.

GSK also noted that “there are significant technical hurdles and complexities associated with the introduction of inhaled respiratory products”. The company added that is studying the judgment “and will be considering an appeal to a higher court”.

Before the news came about the German decision, Justin Smith, an analyst at broker MF Global has echoed GSK’s confidence. In a research note, he said investors have overstated the threats facing the drug and are “underestimating the complexity of Advair's device patents, over-crediting the competition and underestimating Advair's international potential”. He added that sales should keep growing over the next four years, exceeding market expectations by more than 50%.