The benefits of Sanofi and Regeneron's anti-inflammatory drug Dupixent set in quickly during a trial to treat "smoker's lung" and lasted for the duration of the 1-year study, French drugmaker Sanofi said late on Sunday.

The company said it was discussing with major watchdogs across the world whether the trial results are substantial enough to support a regulatory review or whether that will require the results of another ongoing trial.

It said in March in a brief summary of the late-stage trial that Dupixent was associated with a 30% reduction in acute exacerbations of the disease, which is also known as chronic obstructive pulmonary disease (COPD).

This potentially added billions to the French drugmaker's growth prospects but also underscored a heavy reliance on its bestseller.

Dupixent, approved to treat conditions including asthma and eczema, is being jointly developed with Regeneron.

Sanofi presented details on the successful study at the American Thoracic Society congress in Washington over the weekend.

"Within two weeks we saw improvement in lung function and improvement in quality of life," said Naimish Patel, Sanofi head of global development for immunology and inflammation.

"And this was also sustained, out to 52 weeks," he added.

A similar second COPD trial was launched by Sanofi to underpin the statistical reliability of the results, but it remains unclear whether regulators will start a review now or wait for the results of the staggered second trial, expected some time in the first half of 2024.

"We will take these results to regulators and have a discussion about what can be done ahead of the read-out of the second trial," Patel said.

Sanofi previously forecast Dupixent would generate up to 13 billion euros ($14.2 billion) in sales in its best year as it seeks to widen its use across several inflammatory conditions, but excluded COPD from its sales target.

Patel would not comment on any review of the peak sales estimate.