(Reuters) -Regeneron shares fell nearly 13% before the bell on Friday after its experimental drug for patients with a type of lung condition commonly called "smoker's lung" failed a late-stage trial, although it succeeded in another.

Regeneron and partner Sanofi were studying the potential blockbuster drug, itepekimab, as a treatment for chronic obstructive pulmonary disease (COPD) in adult former smokers.

The condition has limited treatment options and the drug was expected to target a broader patient population compared to Regeneron and Sanofi's blockbuster Dupixent, which is also approved for the condition.

But after Friday's data, Barclays analyst Emily Field said Dupixent is likely to remain the first choice for doctors.

GSK's Nucala, approved recently for COPD, is also a blockbuster drug.

Nearly 16 million U.S. adults suffer from COPD, according to government data.

Regeneron's shares, which have already fallen 15% this year, were trading at $530 in premarket trading. The company has a market capitalization of $65.36 billion.

The company's itepekimab showed a significant reduction in exacerbations or flare-ups in the condition by 27% compared to placebo at 52 weeks in a 1,127-patient study.

But the second study - which had enrolled fewer former smokers compared to the first - did not meet its goal although a benefit was seen earlier in the trial.

The experimental drug, which is being jointly developed by Regeneron and Sanofi, binds to and inhibits interleukin-33, a type of protein that causes inflammation in COPD.

COPD is a common lung disease causing restricted airflow and breathing problems. It typically affects smokers, but can also be caused by pollutants.

Sanofi and Regeneron are assessing the data and will discuss with regulatory authorities to evaluate their next steps, the companies said.

Regeneron's price to earnings ratio, a common benchmark for valuing stocks, was 16.15, compared with 13.62 for Gilead and 7.29 for Bristol Myers Squibb ( BMY ).

(Reporting by Sriparna Roy in Bengaluru; Editing by Shinjini Ganguli)