Hikma Pharmaceuticals (HKMPY  fell sharply in London ahead of a crucial decision by the U.S. Food & Drug Administration on whether to approve its generic Advair asthma treatment. 

Price action in the stock raises the question of whether the decision has made its way to the market on the quiet or if investors are just bearish on the generic drugmaker's prospect for success. 

Hikma is expected to hear of the FDA's decision on Wed. May 10 but representatives for the company could not immediately be reached for comment when contacted by TheStreet Wednesday. 

Hikma stock was down by more than 3% in London, at 1,920 pence, which was in stark contrast to the almost 1% gain printed by the Stoxx Europe 600 TMI Pharmaceuticals earlier in the session. 

"Certain new launches are expected to contribute around 15% of Generics revenue in 2017, primarily generic Advair, which is assumed to be launched in the second half of the year," the company said in its latest annual report. 

Hikma pulled in 62% of its revenue from the U.S. last year, equating to sales of $1.21 billion.

Advair is a blockbuster asthma treatment pioneered by Glaxo (GSK - Get Report) although it lost the patent in 2010 and has since been bracing for a flood of generics to hit the market. Glaxo stock was up by 1% in noon trading, changing hands at 1,616 pence, slightly ahead of gains for the broader sector. 

Mylan (MYL - Get Report) , Hikma and Vectura (VEGPF  all have Advair generics in the pipeline. Mylan's was knocked back by the FDA in March.

Glaxo made £752 million ($973 million) from the drug in the first-quarter of this year alone. In 2015 Advair pulled-in £3.7 billion for the British drugmaker, down approximately 30% from their peak in 2013, but still accounting for 15% of total group sales.