US regulators have approved GlaxoSmithKline's treatment for chronic obstructive pulmonary disease, but the excitement was cooled by news that Denmark has approved the sale of a generic copy of GSK's biggest product, Advair.On Wednesday evening Glaxo and Theravance announced that the US Food and Drug Administration (FDA) has approved Anoro Ellipta as a treatment for the long-term, once-daily, maintenance treatment of airflow obstruction in patients with chronic obstructive pulmonary disease (COPD), including chronic bronchitis and/or emphysema. Broker Jefferies predicts peak sales of around $2bn for Anoro in 2019.But rival drug makers Sandoz and Vectura also announced the first EU approval for generic Advair, likely to be at a discount to the pricing of GSK's product.Approval in Denmark confirms analyst expectations that an increasingly competitive EU respiratory market may see further reference pricing, which would hit Glaxo's Advair and Breo (and AstraZeneca's Symbicort).Jefferies suggested that seven other EU states will now either accept the Danish assessment, or may raise further questions before making their own decision on granting a respective approval."We would therefore expect to hear of a number of further approvals on a country by country basis over the next few months. As usual, pricing negotiations will then have to take place in each individual country before AirFluSal can launch."Shares in GSK were up 1.4% on Thursday to 1,569.5p at 10:49.OH