ZURICH, Dec 8 (Reuters) - Novartis said its copycat version of Amgen's Neupogen for patients with low white blood cell counts works as well as the original drug in a late-stage trial.

The medicine, made by Novartis' generics arm Sandoz, was being tested in patients with breast cancer undergoing chemotherapy, which often knocks out their white blood cells, giving rise to a condition known as neutropenia.

Results of the Phase III study also showed switching at each cycle between the original drug, also known as filgrastim, and the experimental copy had no impact on efficacy and safety, Novartis said on Monday.

The data will be used to support Sandoz' application for approval of a copycat filgrastim, which was accepted by U.S. regulators at the end of July under a new pathway for so-called biosimilar drugs.

Sandoz is the world leader in cheaper copies of biotech medicines known as biosimilars, which are expected to account for approximately one quarter of the $100 billion worth of sales stemming from off-patent biological drugs by the end of the decade.

The generics company already sells a biosimilar version of Amgen's drug in more than 40 other countries, but the United States has been slower than other markets to establish a regulatory framework for biosimilars.

Sandoz currently sells three biosimilars outside the United States and has a further six molecules in late-stage development.

(Reporting by Caroline Copley, editing by Louise Heavens)