Generic erosion, among other factors, could cause the asthma drug market to decline from $13.4bn in 2009 to less than $12.9bn in 2019, according to a new report.

The report by Decision Resources said generic erosion, increased product competition and restrictive reimbursement environments will cause the asthma drug market to decline in the US, France, Germany, Italy, Spain, the UK and Japan.

Loss of brand exclusivity for Merck/Kyorin’s Singulair, followed by the entry of generic versions in 2012, is expected to be one of the prime culprits for the overall decline.

Other key brands that will experience declining sales include GlaxoSmithKline’s Advair/Seretide/Adoair and AstraZeneca/Astellas’s Symbicort.

The report also said that emerging agents will face the challenge of differentiating themselves from available therapies.