(Adds details, background on disease, share movement)
July 23 (Reuters) - U.S. Food and Drug Administration staff reviewers have raised doubts over the effectiveness of GlaxoSmithKline Plc's drug Nucala in treating a disease that limits airflow to the lungs.
GSK's U.S.-listed shares were down 1.8 percent at $41.11.
Nucala, already approved for treating severe asthma patients, is being reviewed by the FDA for reducing a sudden worsening of symptoms of chronic obstructive pulmonary disease (COPD).
In documents posted here on the regulator's website on Monday, FDA staff said questions remained as to whether data submitted by GSK provided evidence of the drug's effectiveness.
The FDA staff highlighted the drug's failure to meet a statistical threshold for effectiveness in one of the clinical trials, and uncertainty in defining group of patients that could benefit from the treatment.
An expert panel to the FDA is expected to vote on the efficacy and safety of the treatment on Wednesday. While the FDA is not obliged to follow the advice of its experts, it generally does.
Nucala is a monoclonal antibody that inhibits interleukin-5, which helps regulate eosinophils, a type of white blood cell that contributes to asthma. The over-production of eosinophils can cause inflammation in the lungs.
Wednesday's FDA panel meeting will also discuss the relevance of blood eosinophils in COPD patients.
GSK's Trelegy Ellipta was the first once-daily triple medicine for COPD to market, putting it ahead of rivals such as AstraZeneca and Novartis
People with COPD are at increased risk of developing heart disease, lung cancer and a variety of other conditions. COPD affects an estimated 30 million individuals in the United States.
GSK's London-listed shares were marginally up on Monday, following a report on Friday of the drugmaker considering a break up of the group. (Reporting by Manas Mishra in Bengaluru; Editing by Shailesh Kuber)